diff --git a/.hgignore b/.hgignore
--- a/.hgignore
+++ b/.hgignore
@@ -18,3 +18,8 @@
 Session.vim
 .build
 .pytest_cache
+env/
+.eggs/
+libervia_backend.egg-info/
+.mypy_cache/
+twisted/plugins/dropin.cache
diff --git a/dev-requirements.txt b/dev-requirements.txt
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -1,4 +1,8 @@
 -r requirements.txt
 
+lxml-stubs
+
+mypy
+pylint
 pytest
 pytest_twisted
diff --git a/pylintrc b/pylintrc
new file mode 100644
--- /dev/null
+++ b/pylintrc
@@ -0,0 +1,498 @@
+[MASTER]
+
+# A comma-separated list of package or module names from where C extensions may
+# be loaded. Extensions are loading into the active Python interpreter and may
+# run arbitrary code.
+extension-pkg-allow-list=lxml.etree
+
+# Add files or directories to the blacklist. They should be base names, not
+# paths.
+ignore=CVS
+
+# Add files or directories matching the regex patterns to the blacklist. The
+# regex matches against base names, not paths.
+ignore-patterns=
+
+# Python code to execute, usually for sys.path manipulation such as
+# pygtk.require().
+#init-hook=
+
+# Use multiple processes to speed up Pylint. Specifying 0 will auto-detect the
+# number of processors available to use.
+jobs=1
+
+# Control the amount of potential inferred values when inferring a single
+# object. This can help the performance when dealing with large functions or
+# complex, nested conditions.
+limit-inference-results=100
+
+# List of plugins (as comma separated values of python module names) to load,
+# usually to register additional checkers.
+load-plugins=
+
+# Pickle collected data for later comparisons.
+persistent=yes
+
+# Specify a configuration file.
+#rcfile=
+
+# When enabled, pylint would attempt to guess common misconfiguration and emit
+# user-friendly hints instead of false-positive error messages.
+suggestion-mode=yes
+
+# Allow loading of arbitrary C extensions. Extensions are imported into the
+# active Python interpreter and may run arbitrary code.
+unsafe-load-any-extension=no
+
+
+[MESSAGES CONTROL]
+
+# Only show warnings with the listed confidence levels. Leave empty to show
+# all. Valid levels: HIGH, INFERENCE, INFERENCE_FAILURE, UNDEFINED.
+confidence=
+
+# Disable the message, report, category or checker with the given id(s). You
+# can either give multiple identifiers separated by comma (,) or put this
+# option multiple times (only on the command line, not in the configuration
+# file where it should appear only once). You can also use "--disable=all" to
+# disable everything first and then reenable specific checks. For example, if
+# you want to run only the similarities checker, you can use "--disable=all
+# --enable=similarities". If you want to run only the classes checker, but have
+# no Warning level messages displayed, use "--disable=all --enable=classes
+# --disable=W".
+disable=missing-module-docstring,
+        duplicate-code,
+        fixme,
+        logging-fstring-interpolation
+
+# Enable the message, report, category or checker with the given id(s). You can
+# either give multiple identifier separated by comma (,) or put this option
+# multiple time (only on the command line, not in the configuration file where
+# it should appear only once). See also the "--disable" option for examples.
+enable=useless-suppression
+
+
+[REPORTS]
+
+# Python expression which should return a score less than or equal to 10. You
+# have access to the variables 'error', 'warning', 'refactor', and 'convention'
+# which contain the number of messages in each category, as well as 'statement'
+# which is the total number of statements analyzed. This score is used by the
+# global evaluation report (RP0004).
+evaluation=10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)
+
+# Template used to display messages. This is a python new-style format string
+# used to format the message information. See doc for all details.
+#msg-template=
+
+# Set the output format. Available formats are text, parseable, colorized, json
+# and msvs (visual studio). You can also give a reporter class, e.g.
+# mypackage.mymodule.MyReporterClass.
+output-format=text
+
+# Tells whether to display a full report or only the messages.
+reports=no
+
+# Activate the evaluation score.
+score=yes
+
+
+[REFACTORING]
+
+# Maximum number of nested blocks for function / method body
+max-nested-blocks=5
+
+# Complete name of functions that never returns. When checking for
+# inconsistent-return-statements if a never returning function is called then
+# it will be considered as an explicit return statement and no message will be
+# printed.
+never-returning-functions=sys.exit
+
+
+[SPELLING]
+
+# Limits count of emitted suggestions for spelling mistakes.
+max-spelling-suggestions=4
+
+# Spelling dictionary name. Available dictionaries: none. To make it work,
+# install the python-enchant package.
+spelling-dict=
+
+# List of comma separated words that should not be checked.
+spelling-ignore-words=
+
+# A path to a file that contains the private dictionary; one word per line.
+spelling-private-dict-file=
+
+# Tells whether to store unknown words to the private dictionary (see the
+# --spelling-private-dict-file option) instead of raising a message.
+spelling-store-unknown-words=no
+
+
+[VARIABLES]
+
+# List of additional names supposed to be defined in builtins. Remember that
+# you should avoid defining new builtins when possible.
+additional-builtins=
+
+# Tells whether unused global variables should be treated as a violation.
+allow-global-unused-variables=no
+
+# List of strings which can identify a callback function by name. A callback
+# name must start or end with one of those strings.
+callbacks=cb_,
+          _cb
+
+# A regular expression matching the name of dummy variables (i.e. expected to
+# not be used).
+dummy-variables-rgx=_+$|(_[a-zA-Z0-9_]*[a-zA-Z0-9]+?$)|dummy|^ignored_|^unused_
+
+# Argument names that match this expression will be ignored. Default to name
+# with leading underscore.
+ignored-argument-names=_.*|^ignored_|^unused_
+
+# Tells whether we should check for unused import in __init__ files.
+init-import=no
+
+# List of qualified module names which can have objects that can redefine
+# builtins.
+redefining-builtins-modules=six.moves,past.builtins,future.builtins,builtins,io
+
+
+[LOGGING]
+
+# Format style used to check logging format string. `old` means using %
+# formatting, `new` is for `{}` formatting,and `fstr` is for f-strings.
+logging-format-style=old
+
+# Logging modules to check that the string format arguments are in logging
+# function parameter format.
+logging-modules=logging
+
+
+[FORMAT]
+
+# Expected format of line ending, e.g. empty (any line ending), LF or CRLF.
+expected-line-ending-format=
+
+# Regexp for a line that is allowed to be longer than the limit.
+ignore-long-lines=^\s*(# )?<?https?://\S+>?$
+
+# Number of spaces of indent required inside a hanging or continued line.
+indent-after-paren=4
+
+# String used as indentation unit. This is usually "    " (4 spaces) or "\t" (1
+# tab).
+indent-string='    '
+
+# Maximum number of characters on a single line.
+max-line-length=90
+
+# Maximum number of lines in a module.
+max-module-lines=10000
+
+# Allow the body of a class to be on the same line as the declaration if body
+# contains single statement.
+single-line-class-stmt=no
+
+# Allow the body of an if to be on the same line as the test if there is no
+# else.
+single-line-if-stmt=yes
+
+
+[TYPECHECK]
+
+# List of decorators that produce context managers, such as
+# contextlib.contextmanager. Add to this list to register other decorators that
+# produce valid context managers.
+contextmanager-decorators=contextlib.contextmanager
+
+# List of members which are set dynamically and missed by pylint inference
+# system, and so shouldn't trigger E1101 when accessed. Python regular
+# expressions are accepted.
+generated-members=
+
+# Tells whether missing members accessed in mixin class should be ignored. A
+# mixin class is detected if its name ends with "mixin" (case insensitive).
+ignore-mixin-members=yes
+
+# Tells whether to warn about missing members when the owner of the attribute
+# is inferred to be None.
+ignore-none=no
+
+# This flag controls whether pylint should warn about no-member and similar
+# checks whenever an opaque object is returned when inferring. The inference
+# can return multiple potential results while evaluating a Python object, but
+# some branches might not be evaluated, which results in partial inference. In
+# that case, it might be useful to still emit no-member and other checks for
+# the rest of the inferred objects.
+ignore-on-opaque-inference=no
+
+# List of class names for which member attributes should not be checked (useful
+# for classes with dynamically set attributes). This supports the use of
+# qualified names.
+ignored-classes=optparse.Values,thread._local,_thread._local
+
+# List of module names for which member attributes should not be checked
+# (useful for modules/projects where namespaces are manipulated during runtime
+# and thus existing member attributes cannot be deduced by static analysis). It
+# supports qualified module names, as well as Unix pattern matching.
+ignored-modules=
+
+# Show a hint with possible names when a member name was not found. The aspect
+# of finding the hint is based on edit distance.
+missing-member-hint=yes
+
+# The minimum edit distance a name should have in order to be considered a
+# similar match for a missing member name.
+missing-member-hint-distance=1
+
+# The total number of similar names that should be taken in consideration when
+# showing a hint for a missing member.
+missing-member-max-choices=1
+
+# List of decorators that change the signature of a decorated function.
+signature-mutators=
+
+
+[STRING]
+
+# This flag controls whether the implicit-str-concat-in-sequence should
+# generate a warning on implicit string concatenation in sequences defined over
+# several lines.
+check-str-concat-over-line-jumps=no
+
+
+[SIMILARITIES]
+
+# Ignore comments when computing similarities.
+ignore-comments=yes
+
+# Ignore docstrings when computing similarities.
+ignore-docstrings=yes
+
+# Ignore imports when computing similarities.
+ignore-imports=no
+
+# Minimum lines number of a similarity.
+min-similarity-lines=4
+
+
+[BASIC]
+
+# Naming style matching correct argument names.
+argument-naming-style=snake_case
+
+# Regular expression matching correct argument names. Overrides argument-
+# naming-style.
+#argument-rgx=
+
+# Naming style matching correct attribute names.
+attr-naming-style=snake_case
+
+# Regular expression matching correct attribute names. Overrides attr-naming-
+# style.
+#attr-rgx=
+
+# Bad variable names which should always be refused, separated by a comma.
+bad-names=foo,
+          bar,
+          baz,
+          toto,
+          tutu,
+          tata
+
+# Naming style matching correct class attribute names.
+class-attribute-naming-style=UPPER_CASE
+
+# Regular expression matching correct class attribute names. Overrides class-
+# attribute-naming-style.
+#class-attribute-rgx=
+
+# Naming style matching correct class names.
+class-naming-style=PascalCase
+
+# Regular expression matching correct class names. Overrides class-naming-
+# style.
+#class-rgx=
+
+# Naming style matching correct constant names.
+const-naming-style=any
+
+# Regular expression matching correct constant names. Overrides const-naming-
+# style.
+#const-rgx=
+
+# Minimum line length for functions/classes that require docstrings, shorter
+# ones are exempt.
+docstring-min-length=-1
+
+# Naming style matching correct function names.
+function-naming-style=snake_case
+
+# Regular expression matching correct function names. Overrides function-
+# naming-style.
+#function-rgx=
+
+# Good variable names which should always be accepted, separated by a comma.
+good-names=i,
+           j,
+           e, # exceptions in except blocks
+           _
+
+# Include a hint for the correct naming format with invalid-name.
+include-naming-hint=no
+
+# Naming style matching correct inline iteration names.
+inlinevar-naming-style=any
+
+# Regular expression matching correct inline iteration names. Overrides
+# inlinevar-naming-style.
+#inlinevar-rgx=
+
+# Naming style matching correct method names.
+method-naming-style=snake_case
+
+# Regular expression matching correct method names. Overrides method-naming-
+# style.
+#method-rgx=
+
+# Naming style matching correct module names.
+module-naming-style=snake_case
+
+# Regular expression matching correct module names. Overrides module-naming-
+# style.
+#module-rgx=
+
+# Colon-delimited sets of names that determine each other's naming style when
+# the name regexes allow several styles.
+name-group=
+
+# Regular expression which should only match function or class names that do
+# not require a docstring.
+no-docstring-rgx=^_
+
+# List of decorators that produce properties, such as abc.abstractproperty. Add
+# to this list to register other decorators that produce valid properties.
+# These decorators are taken in consideration only for invalid-name.
+property-classes=abc.abstractproperty
+
+# Naming style matching correct variable names.
+variable-naming-style=snake_case
+
+# Regular expression matching correct variable names. Overrides variable-
+# naming-style.
+#variable-rgx=
+
+
+[MISCELLANEOUS]
+
+# List of note tags to take in consideration, separated by a comma.
+notes=FIXME,
+      XXX,
+      TODO
+
+
+[IMPORTS]
+
+# List of modules that can be imported at any level, not just the top level
+# one.
+allow-any-import-level=
+
+# Allow wildcard imports from modules that define __all__.
+allow-wildcard-with-all=no
+
+# Analyse import fallback blocks. This can be used to support both Python 2 and
+# 3 compatible code, which means that the block might have code that exists
+# only in one or another interpreter, leading to false positives when analysed.
+analyse-fallback-blocks=yes
+
+# Deprecated modules which should not be used, separated by a comma.
+deprecated-modules=optparse,tkinter.tix
+
+# Create a graph of external dependencies in the given file (report RP0402 must
+# not be disabled).
+ext-import-graph=
+
+# Create a graph of every (i.e. internal and external) dependencies in the
+# given file (report RP0402 must not be disabled).
+import-graph=
+
+# Create a graph of internal dependencies in the given file (report RP0402 must
+# not be disabled).
+int-import-graph=
+
+# Force import order to recognize a module as part of the standard
+# compatibility libraries.
+known-standard-library=
+
+# Force import order to recognize a module as part of a third party library.
+known-third-party=enchant
+
+# Couples of modules and preferred modules, separated by a comma.
+preferred-modules=
+
+
+[CLASSES]
+
+# List of method names used to declare (i.e. assign) instance attributes.
+defining-attr-methods=__init__,
+                      __new__,
+                      setUp,
+                      __post_init__,
+                      create
+
+# List of member names, which should be excluded from the protected access
+# warning.
+exclude-protected=_asdict,
+                  _fields,
+                  _replace,
+                  _source,
+                  _make
+
+# List of valid names for the first argument in a class method.
+valid-classmethod-first-arg=cls
+
+# List of valid names for the first argument in a metaclass class method.
+valid-metaclass-classmethod-first-arg=cls
+
+
+[DESIGN]
+
+# Maximum number of arguments for function / method.
+max-args=100
+
+# Maximum number of attributes for a class (see R0902).
+max-attributes=100
+
+# Maximum number of boolean expressions in an if statement (see R0916).
+max-bool-expr=10
+
+# Maximum number of branch for function / method body.
+max-branches=100
+
+# Maximum number of locals for function / method body.
+max-locals=100
+
+# Maximum number of parents for a class (see R0901).
+max-parents=10
+
+# Maximum number of public methods for a class (see R0904).
+max-public-methods=100
+
+# Maximum number of return / yield for function / method body.
+max-returns=100
+
+# Maximum number of statements in function / method body.
+max-statements=1000
+
+# Minimum number of public methods for a class (see R0903).
+min-public-methods=0
+
+
+[EXCEPTIONS]
+
+# Exceptions that will emit a warning when being caught. Defaults to
+# "BaseException, Exception".
+overgeneral-exceptions=BaseException,
+                       Exception
diff --git a/sat/core/i18n.py b/sat/core/i18n.py
--- a/sat/core/i18n.py
+++ b/sat/core/i18n.py
@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from typing import Callable, cast
 
 from sat.core.log import getLogger
 
@@ -40,10 +41,10 @@
 except ImportError:
 
     log.warning("gettext support disabled")
-    _ = lambda msg: msg  # Libervia doesn't support gettext
+    _ = cast(Callable[[str], str], lambda msg: msg)  # Libervia doesn't support gettext
 
     def languageSwitch(lang=None):
         pass
 
 
-D_ = lambda msg: msg  # used for deferred translations
+D_ = cast(Callable[[str], str], lambda msg: msg)  # used for deferred translations
diff --git a/sat/plugins/plugin_xep_0082.py b/sat/plugins/plugin_xep_0082.py
new file mode 100644
--- /dev/null
+++ b/sat/plugins/plugin_xep_0082.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+
+# Libervia plugin for XMPP Date and Time Profile formatting and parsing with Python's
+# datetime package
+# Copyright (C) 2022-2022 Tim Henkes (me@syndace.dev)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Type-check with `mypy --strict`
+# Lint with `pylint`
+
+from sat.core.constants import Const as C
+from sat.core.i18n import D_
+from sat.core.sat_main import SAT
+from sat.tools import datetime
+
+
+__all__ = [  # pylint: disable=unused-variable
+    "PLUGIN_INFO",
+    "XEP_0082"
+]
+
+
+PLUGIN_INFO = {
+    C.PI_NAME: "XMPP Date and Time Profiles",
+    C.PI_IMPORT_NAME: "XEP-0082",
+    C.PI_TYPE: C.PLUG_TYPE_MISC,
+    C.PI_PROTOCOLS: [ "XEP-0082" ],
+    C.PI_DEPENDENCIES: [],
+    C.PI_RECOMMENDATIONS: [],
+    C.PI_MAIN: "XEP_0082",
+    C.PI_HANDLER: "no",
+    C.PI_DESCRIPTION: D_("Date and Time Profiles for XMPP"),
+}
+
+
+class XEP_0082:  # pylint: disable=invalid-name
+    """
+    Implementation of the date and time profiles specified in XEP-0082 using Python's
+    datetime module. The legacy format described in XEP-0082 section "4. Migration" is not
+    supported. Reexports of the functions in :mod:`sat.tools.datetime`.
+
+    This is a passive plugin, i.e. it doesn't hook into any triggers to process stanzas
+    actively, but offers API for other plugins to use.
+    """
+
+    def __init__(self, sat: SAT) -> None:
+        """
+        @param sat: The SAT instance.
+        """
+
+    format_date = staticmethod(datetime.format_date)
+    parse_date = staticmethod(datetime.parse_date)
+    format_datetime = staticmethod(datetime.format_datetime)
+    parse_datetime = staticmethod(datetime.parse_datetime)
+    format_time = staticmethod(datetime.format_time)
+    parse_time = staticmethod(datetime.parse_time)
diff --git a/sat/plugins/plugin_xep_0420.py b/sat/plugins/plugin_xep_0420.py
new file mode 100644
--- /dev/null
+++ b/sat/plugins/plugin_xep_0420.py
@@ -0,0 +1,582 @@
+#!/usr/bin/env python3
+
+# Libervia plugin for Stanza Content Encryption
+# Copyright (C) 2022-2022 Tim Henkes (me@syndace.dev)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Type-check with `mypy --strict --disable-error-code no-untyped-call`
+# Lint with `pylint`
+
+from abc import ABC, abstractmethod
+from datetime import datetime
+import enum
+import secrets
+import string
+from typing import Dict, Iterator, List, NamedTuple, Optional, Set, Tuple, Union, cast
+
+from lxml import etree
+
+from sat.core.constants import Const as C
+from sat.core.i18n import D_
+from sat.core.log import Logger, getLogger
+from sat.core.sat_main import SAT
+from sat.tools.xml_tools import ElementParser
+from sat.plugins.plugin_xep_0033 import NS_ADDRESS
+from sat.plugins.plugin_xep_0082 import XEP_0082
+from sat.plugins.plugin_xep_0334 import NS_HINTS
+from sat.plugins.plugin_xep_0359 import NS_SID
+from sat.plugins.plugin_xep_0380 import NS_EME
+from twisted.words.protocols.jabber import jid
+from twisted.words.xish import domish
+
+
+__all__ = [  # pylint: disable=unused-variable
+    "PLUGIN_INFO",
+    "NS_SCE",
+    "XEP_0420",
+    "ProfileRequirementsNotMet",
+    "AffixVerificationFailed",
+    "SCECustomAffix",
+    "SCEAffixPolicy",
+    "SCEProfile",
+    "SCEAffixValues"
+]
+
+
+log = cast(Logger, getLogger(__name__))
+
+
+PLUGIN_INFO = {
+    C.PI_NAME: "SCE",
+    C.PI_IMPORT_NAME: "XEP-0420",
+    C.PI_TYPE: "SEC",
+    C.PI_PROTOCOLS: [ "XEP-0420" ],
+    C.PI_DEPENDENCIES: [ "XEP-0334", "XEP-0082" ],
+    C.PI_RECOMMENDATIONS: [ "XEP-0045", "XEP-0033", "XEP-0359" ],
+    C.PI_MAIN: "XEP_0420",
+    C.PI_HANDLER: "no",
+    C.PI_DESCRIPTION: D_("Implementation of Stanza Content Encryption"),
+}
+
+
+NS_SCE = "urn:xmpp:sce:1"
+
+
+class ProfileRequirementsNotMet(Exception):
+    """
+    Raised by :meth:`XEP_0420.unpack_stanza` in case the requirements formulated by the
+    profile are not met.
+    """
+
+
+class AffixVerificationFailed(Exception):
+    """
+    Raised by :meth:`XEP_0420.unpack_stanza` in case of affix verification failure.
+    """
+
+
+class SCECustomAffix(ABC):
+    """
+    Interface for custom affixes of SCE profiles.
+    """
+
+    @property
+    @abstractmethod
+    def element_name(self) -> str:
+        """
+        @return: The name of the affix's XML element.
+        """
+
+    @property
+    @abstractmethod
+    def element_schema(self) -> str:
+        """
+        @return: The XML schema definition of the affix element's XML structure, i.e. the
+            ``<xs:element/>`` schema element. This element will be referenced using
+            ``<xs:element ref="{element_name}"/>``.
+        """
+
+    @abstractmethod
+    def create(self, stanza: domish.Element) -> domish.Element:
+        """
+        @param stanza: The stanza element which has been processed by
+            :meth:`XEP_0420.pack_stanza`, i.e. all encryptable children have been removed
+            and only the root ``<message/>`` or ``<iq/>`` and unencryptable children
+            remain. Do not modify.
+        @return: An affix element to include in the envelope. The element must have the
+            name :attr:`element_name` and must validate using :attr:`element_schema`.
+        @raise ValueError: if the affix couldn't be built.
+        """
+
+    @abstractmethod
+    def verify(self, stanza: domish.Element, element: domish.Element) -> None:
+        """
+        @param stanza: The stanza element before being processed by
+            :meth:`XEP_0420.unpack_stanza`, i.e. all encryptable children have been
+            removed and only the root ``<message/>`` or ``<iq/>`` and unencryptable
+            children remain. Do not modify.
+        @param element: The affix element to verify.
+        @raise AffixVerificationFailed: on verification failure.
+        """
+
+
+@enum.unique
+class SCEAffixPolicy(enum.Enum):
+    """
+    Policy for the presence of an affix in an SCE envelope.
+    """
+
+    REQUIRED: str = "REQUIRED"
+    OPTIONAL: str = "OPTIONAL"
+    NOT_NEEDED: str = "NOT_NEEDED"
+
+
+class SCEProfile(NamedTuple):
+    # pylint: disable=invalid-name
+    """
+    An SCE profile, i.e. the definition which affixes are required, optional or not needed
+    at all by an SCE-enabled encryption protocol.
+    """
+
+    rpad_policy: SCEAffixPolicy
+    time_policy: SCEAffixPolicy
+    to_policy: SCEAffixPolicy
+    from_policy: SCEAffixPolicy
+    custom_policies: Dict[SCECustomAffix, SCEAffixPolicy]
+
+
+class SCEAffixValues(NamedTuple):
+    # pylint: disable=invalid-name
+    """
+    Structure returned by :meth:`XEP_0420.unpack_stanza` with the parsed/processes values
+    of all affixes included in the envelope. For custom affixes, the whole affix element
+    is returned.
+    """
+
+    rpad: Optional[str]
+    timestamp: Optional[datetime]
+    recipient: Optional[jid.JID]
+    sender: Optional[jid.JID]
+    custom: Dict[SCECustomAffix, domish.Element]
+
+
+ENVELOPE_SCHEMA = """<?xml version="1.0" encoding="utf8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
+    targetNamespace="urn:xmpp:sce:1"
+    xmlns="urn:xmpp:sce:1">
+
+    <xs:element name="envelope">
+        <xs:complexType>
+            <xs:all>
+                <xs:element ref="content"/>
+                <xs:element ref="rpad" minOccurs="0"/>
+                <xs:element ref="time" minOccurs="0"/>
+                <xs:element ref="to" minOccurs="0"/>
+                <xs:element ref="from" minOccurs="0"/>
+                {custom_affix_references}
+            </xs:all>
+        </xs:complexType>
+    </xs:element>
+
+    <xs:element name="content">
+        <xs:complexType>
+            <xs:sequence>
+                <xs:any minOccurs="0" maxOccurs="unbounded" processContents="skip"/>
+            </xs:sequence>
+        </xs:complexType>
+    </xs:element>
+
+    <xs:element name="rpad" type="xs:string"/>
+
+    <xs:element name="time">
+        <xs:complexType>
+            <xs:attribute name="stamp" type="xs:dateTime"/>
+        </xs:complexType>
+    </xs:element>
+
+    <xs:element name="to">
+        <xs:complexType>
+            <xs:attribute name="jid" type="xs:string"/>
+        </xs:complexType>
+    </xs:element>
+
+    <xs:element name="from">
+        <xs:complexType>
+            <xs:attribute name="jid" type="xs:string"/>
+        </xs:complexType>
+    </xs:element>
+
+    {custom_affix_definitions}
+</xs:schema>
+"""
+
+
+class XEP_0420:  # pylint: disable=invalid-name
+    """
+    Implementation of XEP-0420: Stanza Content Encryption under namespace
+    ``urn:xmpp:sce:1``.
+
+    This is a passive plugin, i.e. it doesn't hook into any triggers to process stanzas
+    actively, but offers API for other plugins to use.
+    """
+
+    # Set of namespaces whose elements are never allowed to be transferred in an encrypted
+    # envelope.
+    MUST_BE_PLAINTEXT_NAMESPACES: Set[str] = {
+        NS_HINTS,
+        NS_SID,  # TODO: Not sure whether this ban applies to both stanza-id and origin-id
+        NS_ADDRESS,
+        # Not part of the specification (yet), but just doesn't make sense in an encrypted
+        # envelope:
+        NS_EME
+    }
+
+    # Set of (namespace, element name) tuples that define elements which are never allowed
+    # to be transferred in an encrypted envelope. If all elements under a certain
+    # namespace are forbidden, the namespace can be added to
+    # :attr:`MUST_BE_PLAINTEXT_NAMESPACES` instead.
+    # Note: only full namespaces are forbidden by the spec for now, the following is for
+    # potential future use.
+    MUST_BE_PLAINTEXT_ELEMENTS: Set[Tuple[str, str]] = set()
+
+    def __init__(self, sat: SAT) -> None:
+        """
+        @param sat: The SAT instance.
+        """
+
+    @staticmethod
+    def pack_stanza(profile: SCEProfile, stanza: domish.Element) -> bytes:
+        """Pack a stanza according to Stanza Content Encryption.
+
+        Removes all elements from the stanza except for a few exceptions that explicitly
+        need to be transferred in plaintext, e.g. because they contain hints/instructions
+        for the server on how to process the stanza. Together with the affix elements as
+        requested by the profile, the removed elements are added to an envelope XML
+        structure that builds the plaintext to be encrypted by the SCE-enabled encryption
+        scheme. Optional affixes are always added to the structure, i.e. they are treated
+        by the packing code as if they were required.
+
+        Once built, the envelope structure is serialized to a byte string and returned for
+        the encryption scheme to encrypt and add to the stanza.
+
+        @param profile: The SCE profile, i.e. the definition of affixes to include in the
+            envelope.
+        @param stanza: The stanza to process. Will be modified by the call.
+        @return: The serialized envelope structure that builds the plaintext for the
+            encryption scheme to process.
+        @raise ValueError: if the <to/> or <from/> affixes are requested but the stanza
+            doesn't have the "to"/"from" attribute set to extract the value from. Can also
+            be raised by custom affixes.
+
+        @warning: It is up to the calling code to add a <store/> message processing hint
+            if applicable.
+        """
+
+        # Prepare the envelope and content elements
+        envelope = domish.Element((NS_SCE, "envelope"))
+        content = envelope.addElement((NS_SCE, "content"))
+
+        # Note the serialized byte size of the content element before adding any children
+        empty_content_byte_size = len(content.toXml().encode("utf-8"))
+
+        # Just for type safety
+        stanza_children = cast(List[Union[domish.Element, str]], stanza.children)
+        content_children = cast(List[Union[domish.Element, str]], content.children)
+
+        # Move elements that are not explicitly forbidden from being encrypted from the
+        # stanza to the content element.
+        for child in list(cast(Iterator[domish.Element], stanza.elements())):
+            if (
+                child.uri not in XEP_0420.MUST_BE_PLAINTEXT_NAMESPACES
+                and (child.uri, child.name) not in XEP_0420.MUST_BE_PLAINTEXT_ELEMENTS
+            ):
+                # Remove the child from the stanza
+                stanza_children.remove(child)
+
+                # A namespace of ``None`` can be used on domish elements to inherit the
+                # namespace from the parent. When moving elements from the stanza root to
+                # the content element, however, we don't want elements to inherit the
+                # namespace of the content element. Thus, check for elements with ``None``
+                # for their namespace and set the namespace to jabber:client, which is the
+                # namespace of the parent element.
+                if child.uri is None:
+                    child.uri = C.NS_CLIENT
+                    child.defaultUri = C.NS_CLIENT
+
+                # Add the child with corrected namespaces to the content element
+                content_children.append(child)
+
+        # Add the affixes requested by the profile
+        if profile.rpad_policy is not SCEAffixPolicy.NOT_NEEDED:
+            # The specification defines the rpad affix to contain "[...] a randomly
+            # generated sequence of random length between 0 and 200 characters." This
+            # implementation differs a bit from the specification in that a minimum size
+            # other than 0 is chosen depending on the serialized size of the content
+            # element. This is to prevent the scenario where the encrypted content is
+            # short and the rpad is also randomly chosen to be short, which could allow
+            # guessing the content of a short message. To do so, the rpad length is first
+            # chosen to pad the content to at least 53 bytes, then afterwards another 0 to
+            # 200 bytes are added. Note that single-byte characters are used by this
+            # implementation, thus the number of characters equals the number of bytes.
+            content_byte_size = len(content.toXml().encode("utf-8"))
+            content_byte_size_diff = content_byte_size - empty_content_byte_size
+            rpad_length = max(0, 53 - content_byte_size_diff) + secrets.randbelow(201)
+            rpad_content = "".join(
+                secrets.choice(string.digits + string.ascii_letters + string.punctuation)
+                for __
+                in range(rpad_length)
+            )
+            envelope.addElement((NS_SCE, "rpad"), content=rpad_content)
+
+        if profile.time_policy is not SCEAffixPolicy.NOT_NEEDED:
+            time_element = envelope.addElement((NS_SCE, "time"))
+            time_element["stamp"] = XEP_0082.format_datetime()
+
+        if profile.to_policy is not SCEAffixPolicy.NOT_NEEDED:
+            recipient = cast(Optional[str], stanza.getAttribute("to", None))
+            if recipient is None:
+                raise ValueError(
+                    "<to/> affix requested, but stanza doesn't have the 'to' attribute"
+                    " set."
+                )
+
+            to_element = envelope.addElement((NS_SCE, "to"))
+            to_element["jid"] = jid.JID(recipient).userhost()
+
+        if profile.from_policy is not SCEAffixPolicy.NOT_NEEDED:
+            sender = cast(Optional[str], stanza.getAttribute("from", None))
+            if sender is None:
+                raise ValueError(
+                    "<from/> affix requested, but stanza doesn't have the 'from'"
+                    " attribute set."
+                )
+
+            from_element = envelope.addElement((NS_SCE, "from"))
+            from_element["jid"] = jid.JID(sender).userhost()
+
+        for affix, policy in profile.custom_policies.items():
+            if policy is not SCEAffixPolicy.NOT_NEEDED:
+                envelope.addChild(affix.create(stanza))
+
+        return cast(str, envelope.toXml()).encode("utf-8")
+
+    @staticmethod
+    def unpack_stanza(
+        profile: SCEProfile,
+        stanza: domish.Element,
+        envelope_serialized: bytes
+    ) -> SCEAffixValues:
+        """Unpack a stanza packed according to Stanza Content Encryption.
+
+        Parses the serialized envelope as XML, verifies included affixes and makes sure
+        the requirements of the profile are met, and restores the stanza by moving
+        decrypted elements from the envelope back to the stanza top level.
+
+        @param profile: The SCE profile, i.e. the definition of affixes that have to/may
+            be included in the envelope.
+        @param stanza: The stanza to process. Will be modified by the call.
+        @param envelope_serialized: The serialized envelope, i.e. the plaintext produced
+            by the decryption scheme utilizing SCE.
+        @return: The parsed and processed values of all affixes that were present on the
+            envelope, notably including the timestamp.
+        @raise ValueError: if the serialized envelope element is malformed.
+        @raise ProfileRequirementsNotMet: if one or more affixes required by the profile
+            are missing from the envelope.
+        @raise AffixVerificationFailed: if an affix included in the envelope fails to
+            validate. It doesn't matter whether the affix is required by the profile or
+            not, all affixes included in the envelope are validated and cause this
+            exception to be raised on failure.
+
+        @warning: It is up to the calling code to verify the timestamp, if returned, since
+            the requirements on the timestamp may vary between SCE-enabled protocols.
+        """
+
+        try:
+            envelope_serialized_string = envelope_serialized.decode("utf-8")
+        except UnicodeError as e:
+            raise ValueError("Serialized envelope can't bare parsed as utf-8.") from e
+
+        custom_affixes = set(profile.custom_policies.keys())
+
+        # Make sure the envelope adheres to the schema
+        parser = etree.XMLParser(schema=etree.XMLSchema(etree.XML(ENVELOPE_SCHEMA.format(
+            custom_affix_references="".join(
+                f'<xs:element ref="{custom_affix.element_name}" minOccurs="0"/>'
+                for custom_affix
+                in custom_affixes
+            ),
+            custom_affix_definitions="".join(
+                custom_affix.element_schema
+                for custom_affix
+                in custom_affixes
+            )
+        ).encode("utf-8"))))
+
+        try:
+            etree.fromstring(envelope_serialized_string, parser)
+        except etree.XMLSyntaxError as e:
+            raise ValueError("Serialized envelope doesn't pass schema validation.") from e
+
+        # Prepare the envelope and content elements
+        envelope = cast(domish.Element, ElementParser()(envelope_serialized_string))
+        content = cast(domish.Element, next(envelope.elements(NS_SCE, "content")))
+
+        # Verify the affixes
+        rpad_element = cast(
+            Optional[domish.Element],
+            next(envelope.elements(NS_SCE, "rpad"), None)
+        )
+        time_element = cast(
+            Optional[domish.Element],
+            next(envelope.elements(NS_SCE, "time"), None)
+        )
+        to_element = cast(
+            Optional[domish.Element],
+            next(envelope.elements(NS_SCE, "to"), None)
+        )
+        from_element = cast(
+            Optional[domish.Element],
+            next(envelope.elements(NS_SCE, "from"), None)
+        )
+
+        # The rpad doesn't need verification.
+        rpad_value = None if rpad_element is None else str(rpad_element)
+
+        # The time affix isn't verified other than that the timestamp is parseable.
+        try:
+            timestamp_value = None if time_element is None else \
+                XEP_0082.parse_datetime(time_element["stamp"])
+        except ValueError as e:
+            raise AffixVerificationFailed("Malformed time affix") from e
+
+        # The to affix is verified by comparing the to attribute of the stanza with the
+        # JID referenced by the affix. Note that only bare JIDs are compared as per the
+        # specification.
+        recipient_value: Optional[jid.JID] = None
+        if to_element is not None:
+            recipient_value = jid.JID(to_element["jid"])
+
+            recipient_actual = cast(Optional[str], stanza.getAttribute("to", None))
+            if recipient_actual is None:
+                raise AffixVerificationFailed(
+                    "'To' affix is included in the envelope, but the stanza is lacking a"
+                    " 'to' attribute to compare the value to."
+                )
+
+            recipient_actual_bare_jid = jid.JID(recipient_actual).userhost()
+            recipient_target_bare_jid = recipient_value.userhost()
+
+            if recipient_actual_bare_jid != recipient_target_bare_jid:
+                raise AffixVerificationFailed(
+                    f"Mismatch between actual and target recipient bare JIDs:"
+                    f" {recipient_actual_bare_jid} vs {recipient_target_bare_jid}."
+                )
+
+        # The from affix is verified by comparing the from attribute of the stanza with
+        # the JID referenced by the affix. Note that only bare JIDs are compared as per
+        # the specification.
+        sender_value: Optional[jid.JID] = None
+        if from_element is not None:
+            sender_value = jid.JID(from_element["jid"])
+
+            sender_actual = cast(Optional[str], stanza.getAttribute("from", None))
+            if sender_actual is None:
+                raise AffixVerificationFailed(
+                    "'From' affix is included in the envelope, but the stanza is lacking"
+                    " a 'from' attribute to compare the value to."
+                )
+
+            sender_actual_bare_jid = jid.JID(sender_actual).userhost()
+            sender_target_bare_jid = sender_value.userhost()
+
+            if sender_actual_bare_jid != sender_target_bare_jid:
+                raise AffixVerificationFailed(
+                    f"Mismatch between actual and target sender bare JIDs:"
+                    f" {sender_actual_bare_jid} vs {sender_target_bare_jid}."
+                )
+
+        # Find and verify custom affixes
+        custom_values: Dict[SCECustomAffix, domish.Element] = {}
+        for affix in custom_affixes:
+            element_name = affix.element_name
+            element = cast(
+                Optional[domish.Element],
+                next(envelope.elements(NS_SCE, element_name), None)
+            )
+            if element is not None:
+                affix.verify(stanza, element)
+                custom_values[affix] = element
+
+        # Check whether all affixes required by the profile are present
+        rpad_missing = \
+            profile.rpad_policy is SCEAffixPolicy.REQUIRED and rpad_element is None
+        time_missing = \
+            profile.time_policy is SCEAffixPolicy.REQUIRED and time_element is None
+        to_missing = \
+            profile.to_policy is SCEAffixPolicy.REQUIRED and to_element is None
+        from_missing = \
+            profile.from_policy is SCEAffixPolicy.REQUIRED and from_element is None
+        custom_missing = any(
+            affix not in custom_values
+            for affix, policy
+            in profile.custom_policies.items()
+            if policy is SCEAffixPolicy.REQUIRED
+        )
+
+        if rpad_missing or time_missing or to_missing or from_missing or custom_missing:
+            custom_missing_string = ""
+            for custom_affix in custom_affixes:
+                value = "present" if custom_affix in custom_values else "missing"
+                custom_missing_string += f", [custom]{custom_affix.element_name}={value}"
+
+            raise ProfileRequirementsNotMet(
+                f"SCE envelope is missing affixes required by the profile {profile}."
+                f" Affix presence:"
+                f" rpad={'missing' if rpad_missing else 'present'}"
+                f", time={'missing' if time_missing else 'present'}"
+                f", to={'missing' if to_missing else 'present'}"
+                f", from={'missing' if from_missing else 'present'}"
+                + custom_missing_string
+            )
+
+        # Just for type safety
+        content_children = cast(List[Union[domish.Element, str]], content.children)
+        stanza_children = cast(List[Union[domish.Element, str]], stanza.children)
+
+        # Move elements that are not explicitly forbidden from being encrypted from the
+        # content element to the stanza.
+        for child in list(cast(Iterator[domish.Element], content.elements())):
+            if (
+                child.uri in XEP_0420.MUST_BE_PLAINTEXT_NAMESPACES
+                or (child.uri, child.name) in XEP_0420.MUST_BE_PLAINTEXT_ELEMENTS
+            ):
+                log.warning(
+                    f"An element that MUST be transferred in plaintext was found in an"
+                    f" SCE envelope: {child.toXml()}"
+                )
+            else:
+                # Remove the child from the content element
+                content_children.remove(child)
+
+                # Add the child to the stanza
+                stanza_children.append(child)
+
+        return SCEAffixValues(
+            rpad_value,
+            timestamp_value,
+            recipient_value,
+            sender_value,
+            custom_values
+        )
diff --git a/sat/tools/datetime.py b/sat/tools/datetime.py
new file mode 100644
--- /dev/null
+++ b/sat/tools/datetime.py
@@ -0,0 +1,182 @@
+#!/usr/bin/env python3
+
+# Libervia: XMPP Date and Time profiles as per XEP-0082
+# Copyright (C) 2022-2022 Tim Henkes (me@syndace.dev)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Type-check with `mypy --strict`
+# Lint with `pylint`
+
+from datetime import date, datetime, time, timezone
+import re
+from typing import Optional, Tuple
+
+
+__all__ = [  # pylint: disable=unused-variable
+    "format_date",
+    "parse_date",
+    "format_datetime",
+    "parse_datetime",
+    "format_time",
+    "parse_time"
+]
+
+
+def __parse_fraction_of_a_second(value: str) -> Tuple[str, Optional[int]]:
+    """
+    datetime's strptime only supports up to six digits of the fraction of a seconds, while
+    the XEP-0082 specification allows for any number of digits. This function parses and
+    removes the optional fraction of a second from the input string.
+
+    @param value: The input string, containing a section of the format [.sss].
+    @return: The input string with the fraction of a second removed, and the fraction of a
+        second parsed with microsecond resolution. Returns the unaltered input string and
+        ``None`` if no fraction of a second was found in the input string.
+    """
+
+    #  The following regex matches the optional fraction of a seconds for manual
+    # processing.
+    match = re.search(r"\.(\d*)", value)
+    microsecond: Optional[int] = None
+    if match is not None:
+        # Remove the fraction of a second from the input string
+        value = value[:match.start()] + value[match.end():]
+
+        # datetime supports microsecond resolution for the fraction of a second, thus
+        # limit/pad the parsed fraction of a second to six digits
+        microsecond = int(match.group(1)[:6].ljust(6, '0'))
+
+    return value, microsecond
+
+
+def format_date(value: Optional[date] = None) -> str:
+    """
+    @param value: The date for format. Defaults to the current date in the UTC timezone.
+    @return: The date formatted according to the Date profile specified in XEP-0082.
+
+    @warning: Formatting of the current date in the local timezone may leak geographical
+        information of the sender. Thus, it is advised to only format the current date in
+        UTC.
+    """
+    # CCYY-MM-DD
+
+    # The Date profile of XEP-0082 is equal to the ISO 8601 format.
+    return (datetime.now(timezone.utc).date() if value is None else value).isoformat()
+
+
+def parse_date(value: str) -> date:
+    """
+    @param value: A string containing date information formatted according to the Date
+        profile specified in XEP-0082.
+    @return: The date parsed from the input string.
+    @raise ValueError: if the input string is not correctly formatted.
+    """
+    # CCYY-MM-DD
+
+    # The Date profile of XEP-0082 is equal to the ISO 8601 format.
+    return date.fromisoformat(value)
+
+
+def format_datetime(
+    value: Optional[datetime] = None,
+    include_microsecond: bool = False
+) -> str:
+    """
+    @param value: The datetime to format. Defaults to the current datetime.
+    @param include_microsecond: Include the microsecond of the datetime in the output.
+    @return: The datetime formatted according to the DateTime profile specified in
+        XEP-0082. The datetime is always converted to UTC before formatting to avoid
+        leaking geographical information of the sender.
+    """
+    # CCYY-MM-DDThh:mm:ss[.sss]TZD
+
+    # We format the time in UTC, since the %z formatter of strftime doesn't include colons
+    # to separate hours and minutes which is required by XEP-0082. UTC allows us to put a
+    # simple letter 'Z' as the time zone definition.
+    value = (
+        datetime.now(timezone.utc)
+        if value is None
+        else value.astimezone(timezone.utc)  # pylint: disable=no-member
+    )
+
+    if include_microsecond:
+        return value.strftime("%Y-%m-%dT%H:%M:%S.%fZ")
+
+    return value.strftime("%Y-%m-%dT%H:%M:%SZ")
+
+
+def parse_datetime(value: str) -> datetime:
+    """
+    @param value: A string containing datetime information formatted according to the
+        DateTime profile specified in XEP-0082.
+    @return: The datetime parsed from the input string.
+    @raise ValueError: if the input string is not correctly formatted.
+    """
+    # CCYY-MM-DDThh:mm:ss[.sss]TZD
+
+    value, microsecond = __parse_fraction_of_a_second(value)
+
+    result = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S%z")
+
+    if microsecond is not None:
+        result = result.replace(microsecond=microsecond)
+
+    return result
+
+
+def format_time(value: Optional[time] = None, include_microsecond: bool = False) -> str:
+    """
+    @param value: The time to format. Defaults to the current time in the UTC timezone.
+    @param include_microsecond: Include the microsecond of the time in the output.
+    @return: The time formatted according to the Time profile specified in XEP-0082.
+
+    @warning: Since accurate timezone conversion requires the date to be known, this
+        function cannot convert input times to UTC before formatting. This means that
+        geographical information of the sender may be leaked if a time in local timezone
+        is formatted. Thus, when passing a time to format, it is advised to pass the time
+        in UTC if possible.
+    """
+    # hh:mm:ss[.sss][TZD]
+
+    if value is None:
+        # There is no time.now() method as one might expect, but the current time can be
+        # extracted from a datetime object including time zone information.
+        value = datetime.now(timezone.utc).timetz()
+
+    # The format created by time.isoformat complies with the XEP-0082 Time profile.
+    return value.isoformat("auto" if include_microsecond else "seconds")
+
+
+def parse_time(value: str) -> time:
+    """
+    @param value: A string containing time information formatted according to the Time
+        profile specified in XEP-0082.
+    @return: The time parsed from the input string.
+    @raise ValueError: if the input string is not correctly formatted.
+    """
+    # hh:mm:ss[.sss][TZD]
+
+    value, microsecond = __parse_fraction_of_a_second(value)
+
+    # The format parsed by time.fromisoformat mostly complies with the XEP-0082 Time
+    # profile, except that it doesn't handle the letter Z as time zone information for
+    # UTC. This can be fixed with a simple string replacement of 'Z' with "+00:00", which
+    # is another way to represent UTC.
+    result = time.fromisoformat(value.replace('Z', "+00:00"))
+
+    if microsecond is not None:
+        result = result.replace(microsecond=microsecond)
+
+    return result
diff --git a/sat/tools/utils.py b/sat/tools/utils.py
--- a/sat/tools/utils.py
+++ b/sat/tools/utils.py
@@ -34,6 +34,7 @@
 from twisted.internet import defer
 from sat.core.constants import Const as C
 from sat.core.log import getLogger
+from sat.tools.datetime import format_date, format_datetime
 
 log = getLogger(__name__)
 
@@ -146,18 +147,16 @@
 
     to avoid reveling the timezone, we always return UTC dates
     the string returned by this method is valid with RFC 3339
+    this function redirects to the functions in the :mod:`sat.tools.datetime` module
     @param timestamp(None, float): posix timestamp. If None current time will be used
     @param with_time(bool): if True include the time
     @return(unicode): XEP-0082 formatted date and time
     """
-    template_date = "%Y-%m-%d"
-    template_time = "%H:%M:%SZ"
-    template = (
-        "{}T{}".format(template_date, template_time) if with_time else template_date
+    dtime = datetime.datetime.utcfromtimestamp(
+        time.time() if timestamp is None else timestamp
     )
-    return datetime.datetime.utcfromtimestamp(
-        time.time() if timestamp is None else timestamp
-    ).strftime(template)
+
+    return format_datetime(dtime) if with_time else format_date(dtime.date())
 
 
 def generatePassword(vocabulary=None, size=20):
diff --git a/tests/unit/test_plugin_xep_0082.py b/tests/unit/test_plugin_xep_0082.py
new file mode 100644
--- /dev/null
+++ b/tests/unit/test_plugin_xep_0082.py
@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+
+# Tests for Libervia's XMPP Date and Time Profile formatting and parsing plugin
+# Copyright (C) 2022-2022 Tim Henkes (me@syndace.dev)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Type-check with `mypy --strict`
+# Lint with `pylint`
+
+from datetime import date, datetime, time, timezone
+
+import pytest
+
+from sat.plugins.plugin_xep_0082 import XEP_0082
+
+
+__all__ = [  # pylint: disable=unused-variable
+    "test_date_formatting",
+    "test_date_parsing",
+    "test_datetime_formatting",
+    "test_datetime_parsing",
+    "test_time_formatting",
+    "test_time_parsing"
+]
+
+
+def test_date_formatting() -> None:  # pylint: disable=missing-function-docstring
+    # The following tests don't check the output of format_date directly; instead, they
+    # assume that parse_date rejects incorrect formatting.
+
+    # The date version 0.1 of XEP-0082 was published
+    value = date(2003, 4, 21)
+
+    # Check that the parsed date equals the formatted date
+    assert XEP_0082.parse_date(XEP_0082.format_date(value)) == value
+
+    # Check that a date instance is returned when format_date is called without an
+    # explicit input date
+    assert isinstance(XEP_0082.parse_date(XEP_0082.format_date()), date)
+
+
+def test_date_parsing() -> None:  # pylint: disable=missing-function-docstring
+    # There isn't really a point in testing much more than this
+    assert XEP_0082.parse_date("2003-04-21") == date(2003, 4, 21)
+
+
+def test_datetime_formatting() -> None:  # pylint: disable=missing-function-docstring
+    # The following tests don't check the output of format_datetime directly; instead,
+    # they assume that parse_datetime rejects incorrect formatting.
+
+    # A datetime in UTC
+    value = datetime(1234, 5, 6, 7, 8, 9, 123456, timezone.utc)
+
+    # Check that the parsed datetime equals the formatted datetime except for the
+    # microseconds
+    parsed = XEP_0082.parse_datetime(XEP_0082.format_datetime(value))
+    assert parsed != value
+    assert parsed.replace(microsecond=123456) == value
+
+    # Check that the parsed datetime equals the formatted datetime including microseconds
+    assert XEP_0082.parse_datetime(XEP_0082.format_datetime(value, True)) == value
+
+    # A datetime in some other timezone, from the Python docs of the datetime module
+    value = datetime.fromisoformat("2011-11-04T00:05:23+04:00")
+
+    # Check that the parsed datetime equals the formatted datetime with or without
+    # microseconds
+    assert XEP_0082.parse_datetime(XEP_0082.format_datetime(value)) == value
+    assert XEP_0082.parse_datetime(XEP_0082.format_datetime(value, True)) == value
+
+    # Check that the datetime was converted to UTC while formatting
+    assert XEP_0082.parse_datetime(XEP_0082.format_datetime(value)).tzinfo == timezone.utc
+
+    # Check that a datetime instance is returned when format_datetime is called without an
+    # explicit input
+    # datetime
+    assert isinstance(XEP_0082.parse_datetime(XEP_0082.format_datetime()), datetime)
+    assert isinstance(XEP_0082.parse_datetime(XEP_0082.format_datetime(
+        include_microsecond=True
+    )), datetime)
+    assert XEP_0082.parse_datetime(XEP_0082.format_datetime()).tzinfo == timezone.utc
+
+
+def test_datetime_parsing() -> None:  # pylint: disable=missing-function-docstring
+    # Datetime of the first human steps on the Moon (UTC)
+    value = datetime(1969, 7, 21, 2, 56, 15, tzinfo=timezone.utc)
+
+    # With timezone 'Z', without a fraction of a second
+    assert XEP_0082.parse_datetime("1969-07-21T02:56:15Z") == value
+
+    # With timezone '+04:00', without a fraction of a second
+    assert XEP_0082.parse_datetime("1969-07-21T06:56:15+04:00") == value
+
+    # With timezone '-05:00', without a fraction of a second
+    assert XEP_0082.parse_datetime("1969-07-20T21:56:15-05:00") == value
+
+    # Without timezone, without a fraction of a second
+    with pytest.raises(ValueError):
+        XEP_0082.parse_datetime("1969-07-21T02:56:15")
+
+    # With timezone 'Z', with a fraction of a second consisting of two digits
+    assert XEP_0082.parse_datetime("1969-07-21T02:56:15.12Z") == \
+        value.replace(microsecond=120000)
+
+    # With timezone 'Z', with a fraction of a second consisting of nine digits
+    assert XEP_0082.parse_datetime("1969-07-21T02:56:15.123456789Z") == \
+        value.replace(microsecond=123456)
+
+    # With timezone '+04:00', with a fraction of a second consisting of six digits
+    assert XEP_0082.parse_datetime("1969-07-21T06:56:15.123456+04:00") == \
+        value.replace(microsecond=123456)
+
+    # With timezone '-05:00', with a fraction of a second consisting of zero digits
+    assert XEP_0082.parse_datetime("1969-07-20T21:56:15.-05:00") == value
+
+    # Without timezone, with a fraction of a second consisting of six digits
+    with pytest.raises(ValueError):
+        XEP_0082.parse_datetime("1969-07-21T02:56:15.123456")
+
+
+def test_time_formatting() -> None:  # pylint: disable=missing-function-docstring
+    # The following tests don't check the output of format_time directly; instead, they
+    # assume that parse_time rejects incorrect formatting.
+
+    # A time in UTC
+    value = time(12, 34, 56, 789012, timezone.utc)
+
+    # Check that the parsed time equals the formatted time except for the microseconds
+    parsed = XEP_0082.parse_time(XEP_0082.format_time(value))
+    assert parsed != value
+    assert parsed.replace(microsecond=789012) == value
+
+    # Check that the parsed time equals the formatted time including microseconds
+    assert XEP_0082.parse_time(XEP_0082.format_time(value, True)) == value
+
+    # A time in some other timezone, from the Python docs of the datetime module
+    value = time.fromisoformat("04:23:01+04:00")
+
+    # Check that the parsed time equals the formatted time with or without microseconds
+    assert XEP_0082.parse_time(XEP_0082.format_time(value)) == value
+    assert XEP_0082.parse_time(XEP_0082.format_time(value, True)) == value
+
+    # Check that the time has retained its timezone
+    assert XEP_0082.parse_time(XEP_0082.format_time(value)).tzinfo == value.tzinfo
+
+    # A time without timezone information, from the Python docs of the datetime module
+    value = time.fromisoformat("04:23:01")
+
+    # Check that the parsed time doesn't have timezone information either
+    assert XEP_0082.parse_time(XEP_0082.format_time(value)).tzinfo is None
+
+    # Check that a time instance is returned when format_time is called without an
+    # explicit input date
+    assert isinstance(XEP_0082.parse_time(XEP_0082.format_time()), time)
+    assert isinstance(XEP_0082.parse_time(XEP_0082.format_time(
+        include_microsecond=True
+    )), time)
+    assert XEP_0082.parse_time(XEP_0082.format_time()).tzinfo == timezone.utc
+
+
+def test_time_parsing() -> None:  # pylint: disable=missing-function-docstring
+    # Time for tea
+    value = time(16, 0, 0, tzinfo=timezone.utc)
+
+    # With timezone 'Z', without a fraction of a second
+    assert XEP_0082.parse_time("16:00:00Z") == value
+
+    # With timezone '+04:00', without a fraction of a second
+    assert XEP_0082.parse_time("20:00:00+04:00") == value
+
+    # With timezone '-05:00', without a fraction of a second
+    assert XEP_0082.parse_time("11:00:00-05:00") == value
+
+    # Without a timezone, without a fraction of a second
+    assert XEP_0082.parse_time("16:00:00") == value.replace(tzinfo=None)
+
+    # With timezone 'Z', with a fraction of a second consisting of two digits
+    assert XEP_0082.parse_time("16:00:00.12Z") == value.replace(microsecond=120000)
+
+    # With timezone 'Z', with a fraction of a second consisting of nine digits
+    assert XEP_0082.parse_time("16:00:00.123456789Z") == value.replace(microsecond=123456)
+
+    # With timezone '+04:00', with a fraction of a second consisting of six digits
+    assert XEP_0082.parse_time("20:00:00.123456+04:00") == \
+        value.replace(microsecond=123456)
+
+    # With timezone '-05:00', with a fraction of a second consisting of zero digits
+    assert XEP_0082.parse_time("11:00:00.-05:00") == value
+
+    # Without a timezone, with a fraction of a second consisting of six digits
+    assert XEP_0082.parse_time("16:00:00.123456") == \
+        value.replace(microsecond=123456, tzinfo=None)
diff --git a/tests/unit/test_plugin_xep_0420.py b/tests/unit/test_plugin_xep_0420.py
new file mode 100644
--- /dev/null
+++ b/tests/unit/test_plugin_xep_0420.py
@@ -0,0 +1,581 @@
+#!/usr/bin/env python3
+
+# Tests for Libervia's Stanza Content Encryption plugin
+# Copyright (C) 2022-2022 Tim Henkes (me@syndace.dev)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Type-check with `mypy --strict --disable-error-code no-untyped-call`
+# Lint with `pylint`
+
+from datetime import datetime, timezone
+from typing import Callable, Iterator, Optional, cast
+
+import pytest
+
+from sat.plugins.plugin_xep_0334 import NS_HINTS
+from sat.plugins.plugin_xep_0420 import (
+    NS_SCE, XEP_0420, AffixVerificationFailed, ProfileRequirementsNotMet, SCEAffixPolicy,
+    SCECustomAffix, SCEProfile
+)
+from sat.tools.xml_tools import ElementParser
+from twisted.words.xish import domish
+
+
+__all__ = [  # pylint: disable=unused-variable
+    "test_unpack_matches_original",
+    "test_affixes_included",
+    "test_all_affixes_verified",
+    "test_incomplete_affixes",
+    "test_rpad_affix",
+    "test_time_affix",
+    "test_to_affix",
+    "test_from_affix",
+    "test_custom_affixes",
+    "test_namespace_conversion",
+    "test_non_encryptable_elements",
+    "test_schema_validation"
+]
+
+
+string_to_domish = cast(Callable[[str], domish.Element], ElementParser())
+
+
+class CustomAffixImpl(SCECustomAffix):
+    """
+    A simple custom affix implementation for testing purposes. Verifies the full JIDs of
+    both sender and recipient.
+
+    @warning: This is just an example, an affix element like this might not make sense due
+        to potentially allowed modifications of recipient/sender full JIDs (I don't know
+        enough about XMPP routing to know whether full JIDs are always left untouched by
+        the server).
+    """
+
+    @property
+    def element_name(self) -> str:
+        return "full-jids"
+
+    @property
+    def element_schema(self) -> str:
+        return """<xs:element name="full-jids">
+            <xs:complexType>
+                <xs:attribute name="recipient" type="xs:string"/>
+                <xs:attribute name="sender" type="xs:string"/>
+            </xs:complexType>
+        </xs:element>"""
+
+    def create(self, stanza: domish.Element) -> domish.Element:
+        recipient = cast(Optional[str], stanza.getAttribute("to", None))
+        sender = cast(Optional[str], stanza.getAttribute("from", None))
+
+        if recipient is None or sender is None:
+            raise ValueError(
+                "Stanza doesn't have ``to`` and ``from`` attributes required by the"
+                " full-jids custom affix."
+            )
+
+        element = domish.Element((NS_SCE, "full-jids"))
+        element["recipient"] = recipient
+        element["sender"] = sender
+        return element
+
+    def verify(self, stanza: domish.Element, element: domish.Element) -> None:
+        recipient_target = element["recipient"]
+        recipient_actual = stanza.getAttribute("to")
+
+        sender_target = element["sender"]
+        sender_actual = stanza.getAttribute("from")
+
+        if recipient_actual != recipient_target or sender_actual != sender_target:
+            raise AffixVerificationFailed(
+                f"Full JIDs differ. Recipient: actual={recipient_actual} vs."
+                f" target={recipient_target}; Sender: actual={sender_actual} vs."
+                f" target={sender_target}"
+            )
+
+
+def test_unpack_matches_original() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.OPTIONAL,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.OPTIONAL,
+        custom_policies={ CustomAffixImpl(): SCEAffixPolicy.NOT_NEEDED }
+    )
+
+    stanza_string = (
+        '<message from="foo@example.com" to="bar@example.com"><body>Test with both a body'
+        ' and some other custom element.</body><custom xmlns="urn:xmpp:example:0"'
+        ' test="matches-original">some more content</custom></message>'
+    )
+
+    stanza = string_to_domish(stanza_string)
+
+    envelope_serialized = XEP_0420.pack_stanza(profile, stanza)
+
+    # The stanza should not have child elements any more
+    assert len(list(stanza.elements())) == 0
+
+    XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+
+    # domish.Element doesn't override __eq__, thus we compare the .toXml() strings here in
+    # the hope that serialization for an example as small as this is unique enough to be
+    # compared that way.
+    assert stanza.toXml() == string_to_domish(stanza_string).toXml()
+
+
+def test_affixes_included() -> None:  # pylint: disable=missing-function-docstring
+    custom_affix = CustomAffixImpl()
+
+    profile = SCEProfile(
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.OPTIONAL,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.OPTIONAL,
+        custom_policies={ custom_affix: SCEAffixPolicy.OPTIONAL }
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>
+            Make sure that both the REQUIRED and the OPTIONAL affixes are included.
+        </body>
+    </message>""")
+
+    affix_values = XEP_0420.unpack_stanza(
+        profile,
+        stanza,
+        XEP_0420.pack_stanza(profile, stanza)
+    )
+
+    assert affix_values.rpad is not None
+    assert affix_values.timestamp is not None
+    assert affix_values.recipient is None
+    assert affix_values.sender is not None
+    assert custom_affix in affix_values.custom
+
+
+def test_all_affixes_verified() -> None:  # pylint: disable=missing-function-docstring
+    packing_profile = SCEProfile(
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        custom_policies={}
+    )
+
+    unpacking_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>
+            When unpacking, all affixes are loaded, even those marked as NOT_NEEDED.
+        </body>
+    </message>""")
+
+    envelope_serialized = XEP_0420.pack_stanza(packing_profile, stanza)
+
+    affix_values = XEP_0420.unpack_stanza(unpacking_profile, stanza, envelope_serialized)
+
+    assert affix_values.rpad is not None
+    assert affix_values.timestamp is not None
+    assert affix_values.recipient is not None
+    assert affix_values.sender is not None
+
+    # When unpacking, all affixes are verified, even if they are NOT_NEEDED by the profile
+    stanza = string_to_domish(
+        """<message from="fooo@example.com" to="baz@example.com"></message>"""
+    )
+
+    with pytest.raises(AffixVerificationFailed):
+        XEP_0420.unpack_stanza(unpacking_profile, stanza, envelope_serialized)
+
+
+def test_incomplete_affixes() -> None:  # pylint: disable=missing-function-docstring
+    packing_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    unpacking_profile = SCEProfile(
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.REQUIRED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>Check that all affixes REQUIRED by the profile are present.</body>
+    </message>""")
+
+    with pytest.raises(ProfileRequirementsNotMet):
+        XEP_0420.unpack_stanza(
+            unpacking_profile,
+            stanza,
+            XEP_0420.pack_stanza(packing_profile, stanza)
+        )
+
+    # Do the same but with a custom affix missing
+    custom_affix = CustomAffixImpl()
+
+    packing_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={ custom_affix: SCEAffixPolicy.NOT_NEEDED }
+    )
+
+    unpacking_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={ custom_affix: SCEAffixPolicy.REQUIRED }
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>
+            Check that all affixes REQUIRED by the profile are present, including custom
+            affixes.
+        </body>
+    </message>""")
+
+    with pytest.raises(ProfileRequirementsNotMet):
+        XEP_0420.unpack_stanza(
+            unpacking_profile,
+            stanza,
+            XEP_0420.pack_stanza(packing_profile, stanza)
+        )
+
+
+def test_rpad_affix() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    for _ in range(100):
+        stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+            <body>OK</body>
+        </message>""")
+
+        affix_values = XEP_0420.unpack_stanza(
+            profile,
+            stanza,
+            XEP_0420.pack_stanza(profile, stanza)
+        )
+
+        # Test that the rpad exists and that the content elements are always padded to at
+        # least 53 characters
+        assert affix_values.rpad is not None
+        assert len(affix_values.rpad) >= 53 - len("<body xmlns='jabber:client'>OK</body>")
+
+
+def test_time_affix() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish(
+        """<message from="foo@example.com" to="bar@example.com"></message>"""
+    )
+
+    envelope_serialized = f"""<envelope xmlns="{NS_SCE}">
+        <content>
+            <body xmlns="jabber:client">
+                The time affix is only parsed and not otherwise verified. Not much to test
+                here.
+            </body>
+        </content>
+        <time stamp="1969-07-21T02:56:15Z"/>
+    </envelope>""".encode("utf-8")
+
+    affix_values = XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+    assert affix_values.timestamp == datetime(1969, 7, 21, 2, 56, 15, tzinfo=timezone.utc)
+
+
+def test_to_affix() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.REQUIRED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>Check that the ``to`` affix is correctly added.</body>
+    </message>""")
+
+    envelope_serialized = XEP_0420.pack_stanza(profile, stanza)
+    affix_values = XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+    assert affix_values.recipient is not None
+    assert affix_values.recipient.userhost() == "bar@example.com"
+
+    # Check that a mismatch in recipient bare JID causes an exception to be raised
+    stanza = string_to_domish(
+        """<message from="foo@example.com" to="baz@example.com"></message>"""
+    )
+
+    with pytest.raises(AffixVerificationFailed):
+        XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+
+    # Check that only the bare JID matters
+    stanza = string_to_domish(
+        """<message from="foo@example.com" to="bar@example.com/device"></message>"""
+    )
+
+    affix_values = XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+    assert affix_values.recipient is not None
+    assert affix_values.recipient.userhost() == "bar@example.com"
+
+    stanza = string_to_domish("""<message from="foo@example.com">
+        <body>
+            Check that a missing "to" attribute on the stanza fails stanza packing.
+        </body>
+    </message>""")
+
+    with pytest.raises(ValueError):
+        XEP_0420.pack_stanza(profile, stanza)
+
+
+def test_from_affix() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.REQUIRED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>Check that the ``from`` affix is correctly added.</body>
+    </message>""")
+
+    envelope_serialized = XEP_0420.pack_stanza(profile, stanza)
+    affix_values = XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+    assert affix_values.sender is not None
+    assert affix_values.sender.userhost() == "foo@example.com"
+
+    # Check that a mismatch in sender bare JID causes an exception to be raised
+    stanza = string_to_domish(
+        """<message from="fooo@example.com" to="bar@example.com"></message>"""
+    )
+
+    with pytest.raises(AffixVerificationFailed):
+        XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+
+    # Check that only the bare JID matters
+    stanza = string_to_domish(
+        """<message from="foo@example.com/device" to="bar@example.com"></message>"""
+    )
+
+    affix_values = XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+    assert affix_values.sender is not None
+    assert affix_values.sender.userhost() == "foo@example.com"
+
+    stanza = string_to_domish("""<message to="bar@example.com">
+        <body>
+            Check that a missing "from" attribute on the stanza fails stanza packing.
+        </body>
+    </message>""")
+
+    with pytest.raises(ValueError):
+        XEP_0420.pack_stanza(profile, stanza)
+
+
+def test_custom_affixes() -> None:  # pylint: disable=missing-function-docstring
+    custom_affix = CustomAffixImpl()
+
+    packing_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={ custom_affix: SCEAffixPolicy.REQUIRED }
+    )
+
+    unpacking_profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>
+            If a custom affix is included in the envelope, but not excpected by the
+            recipient, the schema validation should fail.
+        </body>
+    </message>""")
+
+    with pytest.raises(ValueError):
+        XEP_0420.unpack_stanza(
+            unpacking_profile,
+            stanza,
+            XEP_0420.pack_stanza(packing_profile, stanza)
+        )
+
+    profile = packing_profile
+
+    stanza = string_to_domish("""<message from="foo@example.com/device0"
+        to="bar@example.com/Libervia.123">
+        <body>The affix element should be returned as part of the affix values.</body>
+    </message>""")
+
+    affix_values = XEP_0420.unpack_stanza(
+        profile,
+        stanza,
+        XEP_0420.pack_stanza(profile, stanza)
+    )
+
+    assert custom_affix in affix_values.custom
+    assert affix_values.custom[custom_affix].getAttribute("recipient") == \
+        "bar@example.com/Libervia.123"
+    assert affix_values.custom[custom_affix].getAttribute("sender") == \
+        "foo@example.com/device0"
+
+
+def test_namespace_conversion() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = domish.Element((None, "message"))
+    stanza["from"] = "foo@example.com"
+    stanza["to"] = "bar@example.com"
+    stanza.addElement(
+        "body",
+        content=(
+            "This body element has namespace ``None``, which has to be replaced with"
+            " jabber:client."
+        )
+    )
+
+    envelope_serialized = XEP_0420.pack_stanza(profile, stanza)
+    envelope = string_to_domish(envelope_serialized.decode("utf-8"))
+    content = next(cast(Iterator[domish.Element], envelope.elements(NS_SCE, "content")))
+
+    # The body should have been assigned ``jabber:client`` as its namespace
+    assert next(
+        cast(Iterator[domish.Element], content.elements("jabber:client", "body")),
+        None
+    ) is not None
+
+    XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+
+    # The body should still have ``jabber:client`` after unpacking
+    assert next(
+        cast(Iterator[domish.Element], stanza.elements("jabber:client", "body")),
+        None
+    ) is not None
+
+
+def test_non_encryptable_elements() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish("""<message from="foo@example.com" to="bar@example.com">
+        <body>This stanza includes a store hint which must not be encrypted.</body>
+        <store xmlns="urn:xmpp:hints"/>
+    </message>""")
+
+    envelope_serialized = XEP_0420.pack_stanza(profile, stanza)
+    envelope = string_to_domish(envelope_serialized.decode("utf-8"))
+    content = next(cast(Iterator[domish.Element], envelope.elements(NS_SCE, "content")))
+
+    # The store hint must not have been moved to the content element
+    assert next(
+        cast(Iterator[domish.Element], stanza.elements(NS_HINTS, "store")),
+        None
+    ) is not None
+
+    assert next(
+        cast(Iterator[domish.Element], content.elements(NS_HINTS, "store")),
+        None
+    ) is None
+
+    stanza = string_to_domish(
+        """<message from="foo@example.com" to="bar@example.com"></message>"""
+    )
+
+    envelope_serialized = f"""<envelope xmlns="{NS_SCE}">
+        <content>
+            <body xmlns="jabber:client">
+                The store hint must not be moved to the stanza.
+            </body>
+            <store xmlns="urn:xmpp:hints"/>
+        </content>
+    </envelope>""".encode("utf-8")
+
+    XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)
+
+    assert next(
+        cast(Iterator[domish.Element], stanza.elements(NS_HINTS, "store")),
+        None
+    ) is None
+
+
+def test_schema_validation() -> None:  # pylint: disable=missing-function-docstring
+    profile = SCEProfile(
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        SCEAffixPolicy.NOT_NEEDED,
+        custom_policies={}
+    )
+
+    stanza = string_to_domish(
+        """<message from="foo@example.com" to="bar@example.com"></message>"""
+    )
+
+    envelope_serialized = f"""<envelope xmlns="{NS_SCE}">
+        <content>
+            <body xmlns="jabber:client">
+                An unknwon affix should cause a schema validation error.
+            </body>
+            <store xmlns="urn:xmpp:hints"/>
+        </content>
+        <unknown-affix unknown-attr="unknown"/>
+    </envelope>""".encode("utf-8")
+
+    with pytest.raises(ValueError):
+        XEP_0420.unpack_stanza(profile, stanza, envelope_serialized)