diff --git a/.pylint b/.pylint
deleted file mode 100644
index 934f30b..0000000
--- a/.pylint
+++ /dev/null
@@ -1,425 +0,0 @@
-[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-whitelist=
-
-# 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.
-jobs=1
-
-# List of plugins (as comma separated values of python modules names) to load,
-# usually to register additional checkers.
-load-plugins=
-
-# Pickle collected data for later comparisons.
-persistent=yes
-
-# Specify a configuration file.
-#rcfile=
-
-# 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=print-statement,parameter-unpacking,unpacking-in-except,old-raise-syntax,backtick,long-suffix,old-ne-operator,old-octal-literal,import-star-module-level,raw-checker-failed,bad-inline-option,locally-disabled,locally-enabled,file-ignored,suppressed-message,useless-suppression,deprecated-pragma,apply-builtin,basestring-builtin,buffer-builtin,cmp-builtin,coerce-builtin,execfile-builtin,file-builtin,long-builtin,raw_input-builtin,reduce-builtin,standarderror-builtin,unicode-builtin,xrange-builtin,coerce-method,delslice-method,getslice-method,setslice-method,no-absolute-import,old-division,dict-iter-method,dict-view-method,next-method-called,metaclass-assignment,indexing-exception,raising-string,reload-builtin,oct-method,hex-method,nonzero-method,cmp-method,input-builtin,round-builtin,intern-builtin,unichr-builtin,map-builtin-not-iterating,zip-builtin-not-iterating,range-builtin-not-iterating,filter-builtin-not-iterating,using-cmp-argument,eq-without-hash,div-method,idiv-method,rdiv-method,exception-message-attribute,invalid-str-codec,sys-max-int,bad-python3-import,deprecated-string-function,deprecated-str-translate-call
-
-# 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=
-
-
-[REPORTS]
-
-# Python expression which should return a note less than 10 (10 is the highest
-# note). You have access to the variables errors warning, statement which
-# respectively contain the number of errors / warnings messages and the total
-# number of statements analyzed. This 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, eg
-# 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
-
-
-[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
-
-
-[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=79
-
-# Maximum number of lines in a module
-max-module-lines=2000
-
-# List of optional constructs for which whitespace checking is disabled. `dict-
-# separator` is used to allow tabulation in dicts, etc.: {1  : 1,\n222: 2}.
-# `trailing-comma` allows a space between comma and closing bracket: (a, ).
-# `empty-line` allows space-only lines.
-no-space-check=trailing-comma,dict-separator
-
-# 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=no
-
-
-[BASIC]
-
-# Naming hint for argument names
-argument-name-hint=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Regular expression matching correct argument names
-argument-rgx=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Naming hint for attribute names
-attr-name-hint=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Regular expression matching correct attribute names
-attr-rgx=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Bad variable names which should always be refused, separated by a comma
-bad-names=foo,bar,baz,toto,tutu,tata
-
-# Naming hint for class attribute names
-class-attribute-name-hint=([A-Za-z_][A-Za-z0-9_]{2,30}|(__.*__))$
-
-# Regular expression matching correct class attribute names
-class-attribute-rgx=([A-Za-z_][A-Za-z0-9_]{2,30}|(__.*__))$
-
-# Naming hint for class names
-class-name-hint=[A-Z_][a-zA-Z0-9]+$
-
-# Regular expression matching correct class names
-class-rgx=[A-Z_][a-zA-Z0-9]+$
-
-# Naming hint for constant names
-const-name-hint=(([A-Z_][A-Z0-9_]*)|(__.*__))$
-
-# Regular expression matching correct constant names
-const-rgx=(([A-Z_][A-Z0-9_]*)|(__.*__))$
-
-# Minimum line length for functions/classes that require docstrings, shorter
-# ones are exempt.
-docstring-min-length=-1
-
-# Naming hint for function names
-function-name-hint=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Regular expression matching correct function names
-function-rgx=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Good variable names which should always be accepted, separated by a comma
-good-names=i,j,k,ex,Run,_
-
-# Include a hint for the correct naming format with invalid-name
-include-naming-hint=no
-
-# Naming hint for inline iteration names
-inlinevar-name-hint=[A-Za-z_][A-Za-z0-9_]*$
-
-# Regular expression matching correct inline iteration names
-inlinevar-rgx=[A-Za-z_][A-Za-z0-9_]*$
-
-# Naming hint for method names
-method-name-hint=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Regular expression matching correct method names
-method-rgx=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Naming hint for module names
-module-name-hint=(([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+))$
-
-# Regular expression matching correct module names
-module-rgx=(([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+))$
-
-# 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.
-property-classes=abc.abstractproperty
-
-# Naming hint for variable names
-variable-name-hint=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-# Regular expression matching correct variable names
-variable-rgx=(([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$
-
-
-[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
-
-# 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=yes
-
-# 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
-
-
-[VARIABLES]
-
-# List of additional names supposed to be defined in builtins. Remember that
-# you should avoid to define new builtins when possible.
-additional-builtins=
-
-# Tells whether unused global variables should be treated as a violation.
-allow-global-unused-variables=yes
-
-# 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. expectedly
-# not 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,future.builtins
-
-
-[SPELLING]
-
-# Spelling dictionary name. Available dictionaries: none. To make it working
-# install 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 private dictionary; one word per line.
-spelling-private-dict-file=
-
-# Tells whether to store unknown words to indicated private dictionary in
-# --spelling-private-dict-file option instead of raising a message.
-spelling-store-unknown-words=no
-
-
-[MISCELLANEOUS]
-
-# List of note tags to take in consideration, separated by a comma.
-notes=FIXME,XXX,TODO
-
-
-[LOGGING]
-
-# Logging modules to check that the string format arguments are in logging
-# function parameter format
-logging-modules=logging
-
-
-[CLASSES]
-
-# List of method names used to declare (i.e. assign) instance attributes.
-defining-attr-methods=__init__,__new__,setUp
-
-# 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=mcs
-
-
-[DESIGN]
-
-# Maximum number of arguments for function / method
-max-args=5
-
-# Maximum number of attributes for a class (see R0902).
-max-attributes=7
-
-# Maximum number of boolean expressions in a if statement
-max-bool-expr=5
-
-# Maximum number of branch for function / method body
-max-branches=12
-
-# Maximum number of locals for function / method body
-max-locals=15
-
-# Maximum number of parents for a class (see R0901).
-max-parents=7
-
-# Maximum number of public methods for a class (see R0904).
-max-public-methods=20
-
-# Maximum number of return / yield for function / method body
-max-returns=6
-
-# Maximum number of statements in function / method body
-max-statements=50
-
-# Minimum number of public methods for a class (see R0903).
-min-public-methods=2
-
-
-[IMPORTS]
-
-# 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=no
-
-# Deprecated modules which should not be used, separated by a comma
-deprecated-modules=regsub,TERMIOS,Bastion,rexec
-
-# 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
-
-
-[EXCEPTIONS]
-
-# Exceptions that will emit a warning when being caught. Defaults to
-# "Exception"
-overgeneral-exceptions=Exception
diff --git a/.pylintrc b/.pylintrc
new file mode 100644
index 0000000..168e0b7
--- /dev/null
+++ b/.pylintrc
@@ -0,0 +1,52 @@
+[BASIC]
+# We're ok with short funtion argument names.
+# [invalid-name]
+argument-rgx=[a-z_][a-z0-9_]*$
+
+# Allow filter and map.
+# [bad-builtin]
+bad-functions=input
+
+# We prefer docstrings, but we don't require them on all functions.
+# Require them only on long functions (for some value of long).
+# [missing-docstring]
+docstring-min-length=10
+
+# Allow longer methods than the default.
+# [invalid-name]
+method-rgx=[a-z_][a-z0-9_]{2,35}$
+
+# Allow module names containing a dash (but no underscore or uppercase letter).
+# They are whole programs, not meant to be included by another module.
+# [invalid-name]
+module-rgx=(([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+)|[a-z][-0-9a-z]+)$
+
+# Some functions don't need docstrings.
+# [missing-docstring]
+no-docstring-rgx=(run_)main$
+
+# We're ok with short local or global variable names.
+# [invalid-name]
+variable-rgx=[a-z_][a-z0-9_]*$
+
+[DESIGN]
+# Allow more than the default 7 attributes.
+# [too-many-instance-attributes]
+max-attributes=15
+
+[FORMAT]
+# Allow longer modules than the default recommended maximum.
+# [too-many-lines]
+max-module-lines=2000
+
+[MESSAGES CONTROL]
+disable=
+
+[REPORTS]
+# Don't diplay statistics. Just the facts.
+reports=no
+
+[VARIABLES]
+# Allow unused variables if their name starts with an underscore.
+# [unused-argument]
+dummy-variables-rgx=_.*
diff --git a/.travis.yml b/.travis.yml
index 4fc31c9..c45d408 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,7 +31,8 @@
 - tests/scripts/travis-log-failure.sh
 env:
   global:
-    secure: "barHldniAfXyoWOD/vcO+E6/Xm4fmcaUoC9BeKW+LwsHqlDMLvugaJnmLXkSpkbYhVL61Hzf3bo0KPJn88AFc5Rkf8oYHPjH4adMnVXkf3B9ghHCgznqHsAH3choo6tnPxaFgOwOYmLGb382nQxfE5lUdvnM/W/psQjWt66A1+k="
+    - SEED=1
+    - secure: "barHldniAfXyoWOD/vcO+E6/Xm4fmcaUoC9BeKW+LwsHqlDMLvugaJnmLXkSpkbYhVL61Hzf3bo0KPJn88AFc5Rkf8oYHPjH4adMnVXkf3B9ghHCgznqHsAH3choo6tnPxaFgOwOYmLGb382nQxfE5lUdvnM/W/psQjWt66A1+k="
 
 addons:
   apt:
diff --git a/ChangeLog b/ChangeLog
index 3b078c9..0d67ef6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -21,6 +21,16 @@
    * Fix private key DER output in the key_app_writer example. File contents
      were shifted by one byte, creating an invalid ASN.1 tag. Fixed by
      Christian Walther in #2239.
+   * Fix potential memory leak in X.509 self test. Found and fixed by
+     Junhwan Park, #2106.
+   * Reduce stack usage of hkdf tests. Fixes #2195.
+   * Fix 1-byte buffer overflow in mbedtls_mpi_write_string() when
+     used with negative inputs. Found by Guido Vranken in #2404.
+   * Fix bugs in the AEAD test suite which would be exposed by ciphers which
+     either used both encrypt and decrypt key schedules, or which perform padding.
+     GCM and CCM were not affected. Fixed by Jack Lloyd.
+   * Fix incorrect default port number in ssl_mail_client example's usage.
+     Found and fixed by irwir. #2337
 
 Changes
    * Return from various debugging routines immediately if the
diff --git a/README.md b/README.md
index d7a0e9d..94ea84b 100644
--- a/README.md
+++ b/README.md
@@ -35,7 +35,7 @@
 
     make check
 
-The tests need Perl to be built and run. If you don't have Perl installed, you can skip building the tests with:
+The tests need Python to be built and Perl to be run. If you don't have one of them installed, you can skip building the tests with:
 
     make no_test
 
@@ -65,7 +65,7 @@
 
     make test
 
-The test suites need Perl to be built. If you don't have Perl installed, you'll want to disable the test suites with:
+The test suites need Python to be built and Perl to be executed. If you don't have one of these installed, you'll want to disable the test suites with:
 
     cmake -DENABLE_TESTING=Off /path/to/mbedtls_source
 
@@ -133,7 +133,7 @@
 
 The build files for Microsoft Visual Studio are generated for Visual Studio 2010.
 
-The solution file `mbedTLS.sln` contains all the basic projects needed to build the library and all the programs. The files in tests are not generated and compiled, as these need a perl environment as well. However, the selftest program in `programs/test/` is still available.
+The solution file `mbedTLS.sln` contains all the basic projects needed to build the library and all the programs. The files in tests are not generated and compiled, as these need Python and perl environments as well. However, the selftest program in `programs/test/` is still available.
 
 Example programs
 ----------------
@@ -143,7 +143,7 @@
 Tests
 -----
 
-Mbed TLS includes an elaborate test suite in `tests/` that initially requires Perl to generate the tests files (e.g. `test\_suite\_mpi.c`). These files are generated from a `function file` (e.g. `suites/test\_suite\_mpi.function`) and a `data file` (e.g. `suites/test\_suite\_mpi.data`). The `function file` contains the test functions. The `data file` contains the test cases, specified as parameters that will be passed to the test function.
+Mbed TLS includes an elaborate test suite in `tests/` that initially requires Python to generate the tests files (e.g. `test\_suite\_mpi.c`). These files are generated from a `function file` (e.g. `suites/test\_suite\_mpi.function`) and a `data file` (e.g. `suites/test\_suite\_mpi.data`). The `function file` contains the test functions. The `data file` contains the test cases, specified as parameters that will be passed to the test function.
 
 For machines with a Unix shell and OpenSSL (and optionally GnuTLS) installed, additional test scripts are available:
 
diff --git a/circle.yml b/circle.yml
deleted file mode 100644
index eaed02a..0000000
--- a/circle.yml
+++ /dev/null
@@ -1,44 +0,0 @@
-# Purpose:
-# - To test and prove that a new commit in  the mbed TLS repository builds
-# and integrates with mbed-os properly.
-#           AND
-# - To test and prove that the current development head of mbed TLS builds
-# and integrates with the current mbed-os master branch.
-#
-# The script fetches all the prerequisites and builds the mbed TLS 'tls-client'
-# example. This script is triggered by every commit and once each night and the
-# exact behaviour depends on how it was triggered:
-# - If it is a nightly build then it builds the mbed TLS development head with
-#   mbed-os master.
-# - If it was triggered by the commit, then it builds the example with mbed TLS
-#   at that commit and mbed-os at the commit pointed by mbed-os.lib in the
-#   example repository.
-
-test:
-    override:
-        - cd ../mbed-os-example-tls/tls-client/ && mbed compile -m K64F -t GCC_ARM -c
-
-dependencies:
-    pre:
-        # Install gcc-arm
-        - cd .. && wget "https://launchpad.net/gcc-arm-embedded/4.9/4.9-2015-q3-update/+download/gcc-arm-none-eabi-4_9-2015q3-20150921-linux.tar.bz2"
-        - cd .. && tar -xvjf gcc-arm-none-eabi-4_9-2015q3-20150921-linux.tar.bz2
-        - ln -s ../gcc-arm-none-eabi-4_9-2015q3/bin/* ../bin/
-        # Install mbed-cli
-        - cd ../ && git clone https://github.com/ARMmbed/mbed-cli.git
-        - cd ../mbed-cli && sudo -H pip install -e .
-        # Get the sample application
-        - cd ../ && git clone git@github.com:ARMmbed/mbed-os-example-tls.git
-        # Get mbed-os
-        - cd ../mbed-os-example-tls/tls-client && mbed deploy
-        # Update mbed-os to master only if it is a nightly build
-        - >
-            if [ -n "${RUN_NIGHTLY_BUILD}" ]; then
-                cd ../mbed-os-example-tls/tls-client/mbed-os/ && mbed update master;
-            fi
-        # Import mbedtls current revision
-        - ln -s ../../../../../../../mbedtls/ ../mbed-os-example-tls/tls-client/mbed-os/features/mbedtls/importer/TARGET_IGNORE/mbedtls
-        - cd ../mbed-os-example-tls/tls-client/mbed-os/features/mbedtls/importer/ && make
-    override:
-        # Install the missing python packages
-        - cd ../mbed-os-example-tls/tls-client/mbed-os/ && sudo -H pip install -r requirements.txt
diff --git a/library/bignum.c b/library/bignum.c
index 47e4529..4194618 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -582,15 +582,20 @@
     if( radix < 2 || radix > 16 )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
-    n = mbedtls_mpi_bitlen( X );
-    if( radix >=  4 ) n >>= 1;
-    if( radix >= 16 ) n >>= 1;
-    /*
-     * Round up the buffer length to an even value to ensure that there is
-     * enough room for hexadecimal values that can be represented in an odd
-     * number of digits.
-     */
-    n += 3 + ( ( n + 1 ) & 1 );
+    n = mbedtls_mpi_bitlen( X ); /* Number of bits necessary to present `n`. */
+    if( radix >=  4 ) n >>= 1;   /* Number of 4-adic digits necessary to present
+                                  * `n`. If radix > 4, this might be a strict
+                                  * overapproximation of the number of
+                                  * radix-adic digits needed to present `n`. */
+    if( radix >= 16 ) n >>= 1;   /* Number of hexadecimal digits necessary to
+                                  * present `n`. */
+
+    n += 1; /* Terminating null byte */
+    n += 1; /* Compensate for the divisions above, which round down `n`
+             * in case it's not even. */
+    n += 1; /* Potential '-'-sign. */
+    n += ( n & 1 ); /* Make n even to have enough space for hexadecimal writing,
+                     * which always uses an even number of hex-digits. */
 
     if( buflen < n )
     {
@@ -602,7 +607,10 @@
     mbedtls_mpi_init( &T );
 
     if( X->s == -1 )
+    {
         *p++ = '-';
+        buflen--;
+    }
 
     if( radix == 16 )
     {
diff --git a/library/x509.c b/library/x509.c
index 52b5b64..7cc813e 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -1001,8 +1001,8 @@
  */
 int mbedtls_x509_self_test( int verbose )
 {
+    int ret = 0;
 #if defined(MBEDTLS_CERTS_C) && defined(MBEDTLS_SHA256_C)
-    int ret;
     uint32_t flags;
     mbedtls_x509_crt cacert;
     mbedtls_x509_crt clicert;
@@ -1010,6 +1010,7 @@
     if( verbose != 0 )
         mbedtls_printf( "  X.509 certificate load: " );
 
+    mbedtls_x509_crt_init( &cacert );
     mbedtls_x509_crt_init( &clicert );
 
     ret = mbedtls_x509_crt_parse( &clicert, (const unsigned char *) mbedtls_test_cli_crt,
@@ -1019,11 +1020,9 @@
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
 
-        return( ret );
+        goto cleanup;
     }
 
-    mbedtls_x509_crt_init( &cacert );
-
     ret = mbedtls_x509_crt_parse( &cacert, (const unsigned char *) mbedtls_test_ca_crt,
                           mbedtls_test_ca_crt_len );
     if( ret != 0 )
@@ -1031,7 +1030,7 @@
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
 
-        return( ret );
+        goto cleanup;
     }
 
     if( verbose != 0 )
@@ -1043,20 +1042,19 @@
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
 
-        return( ret );
+        goto cleanup;
     }
 
     if( verbose != 0 )
         mbedtls_printf( "passed\n\n");
 
+cleanup:
     mbedtls_x509_crt_free( &cacert  );
     mbedtls_x509_crt_free( &clicert );
-
-    return( 0 );
 #else
     ((void) verbose);
-    return( 0 );
 #endif /* MBEDTLS_CERTS_C && MBEDTLS_SHA1_C */
+    return( ret );
 }
 
 #endif /* MBEDTLS_SELF_TEST */
diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index bbe4c70..c73297c 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -110,9 +110,9 @@
 
 #if defined(MBEDTLS_BASE64_C)
 #define USAGE_AUTH \
-    "    authentication=%%d   default: 0 (disabled)\n"      \
-    "    user_name=%%s        default: \"user\"\n"          \
-    "    user_pwd=%%s         default: \"password\"\n"
+    "    authentication=%%d   default: 0 (disabled)\n"          \
+    "    user_name=%%s        default: \"" DFL_USER_NAME "\"\n" \
+    "    user_pwd=%%s         default: \"" DFL_USER_PWD "\"\n"
 #else
 #define USAGE_AUTH \
     "    authentication options disabled. (Require MBEDTLS_BASE64_C)\n"
@@ -129,17 +129,17 @@
 #endif /* MBEDTLS_FS_IO */
 
 #define USAGE \
-    "\n usage: ssl_mail_client param=<>...\n"               \
-    "\n acceptable parameters:\n"                           \
-    "    server_name=%%s      default: localhost\n"         \
-    "    server_port=%%d      default: 4433\n"              \
-    "    debug_level=%%d      default: 0 (disabled)\n"      \
+    "\n usage: ssl_mail_client param=<>...\n"                 \
+    "\n acceptable parameters:\n"                             \
+    "    server_name=%%s      default: " DFL_SERVER_NAME "\n" \
+    "    server_port=%%d      default: " DFL_SERVER_PORT "\n" \
+    "    debug_level=%%d      default: 0 (disabled)\n"        \
     "    mode=%%d             default: 0 (SSL/TLS) (1 for STARTTLS)\n"  \
-    USAGE_AUTH                                              \
-    "    mail_from=%%s        default: \"\"\n"              \
-    "    mail_to=%%s          default: \"\"\n"              \
-    USAGE_IO                                                \
-    "    force_ciphersuite=<name>    default: all enabled\n"\
+    USAGE_AUTH                                                \
+    "    mail_from=%%s        default: \"\"\n"                \
+    "    mail_to=%%s          default: \"\"\n"                \
+    USAGE_IO                                                  \
+    "    force_ciphersuite=<name>    default: all enabled\n"  \
     " acceptable ciphersuite names:\n"
 
 #if defined(MBEDTLS_CHECK_PARAMS)
@@ -324,7 +324,7 @@
     mbedtls_printf("\n%s", buf);
     if( len && ( ret = mbedtls_net_send( sock_fd, buf, len ) ) <= 0 )
     {
-        mbedtls_printf( " failed\n  ! mbedtls_ssl_write returned %d\n\n", ret );
+        mbedtls_printf( " failed\n  ! mbedtls_net_send returned %d\n\n", ret );
             return -1;
     }
 
@@ -336,7 +336,7 @@
 
         if( ret <= 0 )
         {
-            mbedtls_printf( "failed\n  ! read returned %d\n\n", ret );
+            mbedtls_printf( "failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
             return -1;
         }
 
diff --git a/scripts/abi_check.py b/scripts/abi_check.py
index 8f9cd0f..2a90b68 100755
--- a/scripts/abi_check.py
+++ b/scripts/abi_check.py
@@ -26,8 +26,16 @@
 
 
 class AbiChecker(object):
+    """API and ABI checker."""
 
     def __init__(self, report_dir, old_rev, new_rev, keep_all_reports):
+        """Instantiate the API/ABI checker.
+
+        report_dir: directory for output files
+        old_rev: reference git revision to compare against
+        new_rev: git revision to check
+        keep_all_reports: if false, delete old reports
+        """
         self.repo_path = "."
         self.log = None
         self.setup_logger()
@@ -42,7 +50,8 @@
         self.git_command = "git"
         self.make_command = "make"
 
-    def check_repo_path(self):
+    @staticmethod
+    def check_repo_path():
         current_dir = os.path.realpath('.')
         root_dir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
         if current_dir != root_dir:
@@ -53,12 +62,15 @@
         self.log.setLevel(logging.INFO)
         self.log.addHandler(logging.StreamHandler())
 
-    def check_abi_tools_are_installed(self):
+    @staticmethod
+    def check_abi_tools_are_installed():
         for command in ["abi-dumper", "abi-compliance-checker"]:
             if not shutil.which(command):
                 raise Exception("{} not installed, aborting".format(command))
 
     def get_clean_worktree_for_git_revision(self, git_rev):
+        """Make a separate worktree with git_rev checked out.
+        Do not modify the current worktree."""
         self.log.info(
             "Checking out git worktree for revision {}".format(git_rev)
         )
@@ -76,6 +88,7 @@
         return git_worktree_path
 
     def build_shared_libraries(self, git_worktree_path):
+        """Build the shared libraries in the specified worktree."""
         my_environment = os.environ.copy()
         my_environment["CFLAGS"] = "-g -Og"
         my_environment["SHARED"] = "1"
@@ -92,6 +105,9 @@
             raise Exception("make failed, aborting")
 
     def get_abi_dumps_from_shared_libraries(self, git_ref, git_worktree_path):
+        """Generate the ABI dumps for the specified git revision.
+        It must be checked out in git_worktree_path and the shared libraries
+        must have been built."""
         abi_dumps = {}
         for mbed_module in self.mbedtls_modules:
             output_path = os.path.join(
@@ -117,6 +133,7 @@
         return abi_dumps
 
     def cleanup_worktree(self, git_worktree_path):
+        """Remove the specified git worktree."""
         shutil.rmtree(git_worktree_path)
         worktree_process = subprocess.Popen(
             [self.git_command, "worktree", "prune"],
@@ -130,6 +147,7 @@
             raise Exception("Worktree cleanup failed, aborting")
 
     def get_abi_dump_for_ref(self, git_rev):
+        """Generate the ABI dumps for the specified git revision."""
         git_worktree_path = self.get_clean_worktree_for_git_revision(git_rev)
         self.build_shared_libraries(git_worktree_path)
         abi_dumps = self.get_abi_dumps_from_shared_libraries(
@@ -139,6 +157,9 @@
         return abi_dumps
 
     def get_abi_compatibility_report(self):
+        """Generate a report of the differences between the reference ABI
+        and the new ABI. ABI dumps from self.old_rev and self.new_rev must
+        be available."""
         compatibility_report = ""
         compliance_return_code = 0
         for mbed_module in self.mbedtls_modules:
@@ -188,6 +209,8 @@
         return compliance_return_code
 
     def check_for_abi_changes(self):
+        """Generate a report of ABI differences
+        between self.old_rev and self.new_rev."""
         self.check_repo_path()
         self.check_abi_tools_are_installed()
         self.old_dumps = self.get_abi_dump_for_ref(self.old_rev)
@@ -232,7 +255,9 @@
         )
         return_code = abi_check.check_for_abi_changes()
         sys.exit(return_code)
-    except Exception:
+    except Exception: # pylint: disable=broad-except
+        # Print the backtrace and exit explicitly so as to exit with
+        # status 2, not 1.
         traceback.print_exc()
         sys.exit(2)
 
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 43fbe16..d023c8d 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -150,7 +150,7 @@
 all_final += test-int-ca3-badsign.crt
 server10_int3-bs.pem: server10.crt test-int-ca3-badsign.crt
 	cat server10.crt test-int-ca3-badsign.crt > $@
-all_final += server10-bs_int3-bs.pem
+all_final += server10_int3-bs.pem
 
 rsa_pkcs1_2048_public.pem: server8.key
 	$(OPENSSL)  rsa -in $< -outform PEM -RSAPublicKey_out -out $@
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 53fbc7e..a8d067b 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1247,6 +1247,9 @@
     unset gdb_disable_aslr
 }
 
+support_check_python_files () {
+    type pylint3 >/dev/null 2>/dev/null
+}
 component_check_python_files () {
     msg "Lint: Python scripts"
     record_status tests/scripts/check-python-files.sh
diff --git a/tests/scripts/check-files.py b/tests/scripts/check-files.py
index 005a077..00fd0ed 100755
--- a/tests/scripts/check-files.py
+++ b/tests/scripts/check-files.py
@@ -19,14 +19,23 @@
 import sys
 
 
-class IssueTracker(object):
-    """Base class for issue tracking. Issues should inherit from this and
-    overwrite either issue_with_line if they check the file line by line, or
-    overwrite check_file_for_issue if they check the file as a whole."""
+class FileIssueTracker(object):
+    """Base class for file-wide issue tracking.
+
+    To implement a checker that processes a file as a whole, inherit from
+    this class and implement `check_file_for_issue` and define ``heading``.
+
+    ``files_exemptions``: files whose name ends with a string in this set
+     will not be checked.
+
+    ``heading``: human-readable description of the issue
+    """
+
+    files_exemptions = frozenset()
+    # heading must be defined in derived classes.
+    # pylint: disable=no-member
 
     def __init__(self):
-        self.heading = ""
-        self.files_exemptions = []
         self.files_with_issues = {}
 
     def should_check_file(self, filepath):
@@ -35,23 +44,14 @@
                 return False
         return True
 
-    def issue_with_line(self, line):
-        raise NotImplementedError
-
     def check_file_for_issue(self, filepath):
-        with open(filepath, "rb") as f:
-            for i, line in enumerate(iter(f.readline, b"")):
-                self.check_file_line(filepath, line, i + 1)
+        raise NotImplementedError
 
     def record_issue(self, filepath, line_number):
         if filepath not in self.files_with_issues.keys():
             self.files_with_issues[filepath] = []
         self.files_with_issues[filepath].append(line_number)
 
-    def check_file_line(self, filepath, line, line_number):
-        if self.issue_with_line(line):
-            self.record_issue(filepath, line_number)
-
     def output_file_issues(self, logger):
         if self.files_with_issues.values():
             logger.info(self.heading)
@@ -64,24 +64,44 @@
                     logger.info(filename)
             logger.info("")
 
+class LineIssueTracker(FileIssueTracker):
+    """Base class for line-by-line issue tracking.
 
-class PermissionIssueTracker(IssueTracker):
+    To implement a checker that processes files line by line, inherit from
+    this class and implement `line_with_issue`.
+    """
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Incorrect permissions:"
+    def issue_with_line(self, line, filepath):
+        raise NotImplementedError
+
+    def check_file_line(self, filepath, line, line_number):
+        if self.issue_with_line(line, filepath):
+            self.record_issue(filepath, line_number)
 
     def check_file_for_issue(self, filepath):
-        if not (os.access(filepath, os.X_OK) ==
-                filepath.endswith((".sh", ".pl", ".py"))):
+        with open(filepath, "rb") as f:
+            for i, line in enumerate(iter(f.readline, b"")):
+                self.check_file_line(filepath, line, i + 1)
+
+class PermissionIssueTracker(FileIssueTracker):
+    """Track files with bad permissions.
+
+    Files that are not executable scripts must not be executable."""
+
+    heading = "Incorrect permissions:"
+
+    def check_file_for_issue(self, filepath):
+        is_executable = os.access(filepath, os.X_OK)
+        should_be_executable = filepath.endswith((".sh", ".pl", ".py"))
+        if is_executable != should_be_executable:
             self.files_with_issues[filepath] = None
 
 
-class EndOfFileNewlineIssueTracker(IssueTracker):
+class EndOfFileNewlineIssueTracker(FileIssueTracker):
+    """Track files that end with an incomplete line
+    (no newline character at the end of the last line)."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Missing newline at end of file:"
+    heading = "Missing newline at end of file:"
 
     def check_file_for_issue(self, filepath):
         with open(filepath, "rb") as f:
@@ -89,11 +109,11 @@
                 self.files_with_issues[filepath] = None
 
 
-class Utf8BomIssueTracker(IssueTracker):
+class Utf8BomIssueTracker(FileIssueTracker):
+    """Track files that start with a UTF-8 BOM.
+    Files should be ASCII or UTF-8. Valid UTF-8 does not start with a BOM."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "UTF-8 BOM present:"
+    heading = "UTF-8 BOM present:"
 
     def check_file_for_issue(self, filepath):
         with open(filepath, "rb") as f:
@@ -101,79 +121,76 @@
                 self.files_with_issues[filepath] = None
 
 
-class LineEndingIssueTracker(IssueTracker):
+class LineEndingIssueTracker(LineIssueTracker):
+    """Track files with non-Unix line endings (i.e. files with CR)."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Non Unix line endings:"
+    heading = "Non Unix line endings:"
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"\r" in line
 
 
-class TrailingWhitespaceIssueTracker(IssueTracker):
+class TrailingWhitespaceIssueTracker(LineIssueTracker):
+    """Track lines with trailing whitespace."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Trailing whitespace:"
-        self.files_exemptions = [".md"]
+    heading = "Trailing whitespace:"
+    files_exemptions = frozenset(".md")
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return line.rstrip(b"\r\n") != line.rstrip()
 
 
-class TabIssueTracker(IssueTracker):
+class TabIssueTracker(LineIssueTracker):
+    """Track lines with tabs."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Tabs present:"
-        self.files_exemptions = [
-            "Makefile", "generate_visualc_files.pl"
-        ]
+    heading = "Tabs present:"
+    files_exemptions = frozenset([
+        "Makefile",
+        "generate_visualc_files.pl",
+    ])
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"\t" in line
 
 
-class MergeArtifactIssueTracker(IssueTracker):
+class MergeArtifactIssueTracker(LineIssueTracker):
+    """Track lines with merge artifacts.
+    These are leftovers from a ``git merge`` that wasn't fully edited."""
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "Merge artifact:"
+    heading = "Merge artifact:"
 
-    def issue_with_line(self, filepath, line):
+    def issue_with_line(self, line, _filepath):
         # Detect leftover git conflict markers.
         if line.startswith(b'<<<<<<< ') or line.startswith(b'>>>>>>> '):
             return True
         if line.startswith(b'||||||| '): # from merge.conflictStyle=diff3
             return True
         if line.rstrip(b'\r\n') == b'=======' and \
-           not filepath.endswith('.md'):
+           not _filepath.endswith('.md'):
             return True
         return False
 
-    def check_file_line(self, filepath, line, line_number):
-        if self.issue_with_line(filepath, line):
-            self.record_issue(filepath, line_number)
+class TodoIssueTracker(LineIssueTracker):
+    """Track lines containing ``TODO``."""
 
-class TodoIssueTracker(IssueTracker):
+    heading = "TODO present:"
+    files_exemptions = frozenset([
+        os.path.basename(__file__),
+        "benchmark.c",
+        "pull_request_template.md",
+    ])
 
-    def __init__(self):
-        super().__init__()
-        self.heading = "TODO present:"
-        self.files_exemptions = [
-            os.path.basename(__file__),
-            "benchmark.c",
-            "pull_request_template.md",
-        ]
-
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"todo" in line.lower()
 
 
 class IntegrityChecker(object):
+    """Sanity-check files under the current directory."""
 
     def __init__(self, log_file):
+        """Instantiate the sanity checker.
+        Check files under the current directory.
+        Write a report of issues to log_file."""
         self.check_repo_path()
         self.logger = None
         self.setup_logger(log_file)
@@ -197,7 +214,8 @@
             TodoIssueTracker(),
         ]
 
-    def check_repo_path(self):
+    @staticmethod
+    def check_repo_path():
         if not all(os.path.isdir(d) for d in ["include", "library", "tests"]):
             raise Exception("Must be run from Mbed TLS root")
 
diff --git a/tests/scripts/check-python-files.sh b/tests/scripts/check-python-files.sh
index 009ba4c..9290418 100755
--- a/tests/scripts/check-python-files.sh
+++ b/tests/scripts/check-python-files.sh
@@ -9,10 +9,4 @@
 # Run 'pylint' on Python files for programming errors and helps enforcing
 # PEP8 coding standards.
 
-if `hash pylint > /dev/null 2>&1`; then
-    pylint -j 2 tests/scripts/generate_test_code.py --rcfile .pylint
-    pylint -j 2 tests/scripts/test_generate_test_code.py --rcfile .pylint
-    pylint -j 2 tests/scripts/mbedtls_test.py --rcfile .pylint
-else
-    echo "$0: WARNING: 'pylint' not found! Skipping checks on Python files."
-fi
+pylint3 -j 2 scripts/*.py tests/scripts/*.py
diff --git a/tests/scripts/generate_test_code.py b/tests/scripts/generate_test_code.py
index 1258024..1fff099 100755
--- a/tests/scripts/generate_test_code.py
+++ b/tests/scripts/generate_test_code.py
@@ -238,7 +238,7 @@
         if hasattr(parent, '__next__'):
             line = parent.__next__()  # Python 3
         else:
-            line = parent.next()  # Python 2
+            line = parent.next()  # Python 2 # pylint: disable=no-member
         if line is not None:
             self._line_no += 1
             # Convert byte array to string with correct encoding and
diff --git a/tests/scripts/mbedtls_test.py b/tests/scripts/mbedtls_test.py
index c702765..ac2912d 100755
--- a/tests/scripts/mbedtls_test.py
+++ b/tests/scripts/mbedtls_test.py
@@ -37,7 +37,8 @@
 import re
 import os
 import binascii
-from mbed_host_tests import BaseHostTest, event_callback
+
+from mbed_host_tests import BaseHostTest, event_callback # pylint: disable=import-error
 
 
 class TestDataParserError(Exception):
diff --git a/tests/scripts/test_generate_test_code.py b/tests/scripts/test_generate_test_code.py
index 2ef12e1..6d7113e 100755
--- a/tests/scripts/test_generate_test_code.py
+++ b/tests/scripts/test_generate_test_code.py
@@ -22,7 +22,7 @@
 Unit tests for generate_test_code.py
 """
 
-
+# pylint: disable=wrong-import-order
 try:
     # Python 2
     from StringIO import StringIO
@@ -36,6 +36,7 @@
 except ImportError:
     # Python 3
     from unittest.mock import patch
+# pylint: enable=wrong-import-order
 from generate_test_code import gen_dependencies, gen_dependencies_one_line
 from generate_test_code import gen_function_wrapper, gen_dispatch
 from generate_test_code import parse_until_pattern, GeneratorInputError
@@ -336,6 +337,7 @@
         :param length:
         :return:
         """
+        # pylint: disable=unused-argument
         line = super(StringIOWrapper, self).readline()
         if line is not None:
             self.line_no += 1
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index 773c792..54fe1a3 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -976,6 +976,9 @@
     TEST_ASSERT( memcmp( output, clear->x, clear->len ) == 0 );
 
     /* then encrypt the clear->x and make sure we get the same ciphertext and tag->x */
+    TEST_ASSERT( 0 == mbedtls_cipher_setkey( &ctx, key->x, 8 * key->len,
+                                             MBEDTLS_ENCRYPT ) );
+
     memset( output, 0xFF, sizeof( output ) );
     outlen = 0;
 
@@ -984,8 +987,8 @@
                                my_tag, tag->len );
     TEST_ASSERT( ret == 0 );
 
-    TEST_ASSERT( outlen == clear->len );
-    TEST_ASSERT( memcmp( output, cipher->x, clear->len ) == 0 );
+    TEST_ASSERT( outlen == cipher->len );
+    TEST_ASSERT( memcmp( output, cipher->x, cipher->len ) == 0 );
     TEST_ASSERT( memcmp( my_tag, tag->x, tag->len ) == 0 );
 
     /* make sure we didn't overwrite */
diff --git a/tests/suites/test_suite_hkdf.function b/tests/suites/test_suite_hkdf.function
index c85a51a..3e87207 100644
--- a/tests/suites/test_suite_hkdf.function
+++ b/tests/suites/test_suite_hkdf.function
@@ -14,12 +14,16 @@
 {
     int ret;
     size_t ikm_len, salt_len, info_len, okm_len;
-    unsigned char ikm[1024] = { '\0' };
-    unsigned char salt[1024] = { '\0' };
-    unsigned char info[1024] = { '\0' };
-    unsigned char expected_okm[1024] = { '\0' };
-    unsigned char okm[1024] = { '\0' };
-    unsigned char okm_string[1000] = { '\0' };
+    unsigned char ikm[128] = { '\0' };
+    unsigned char salt[128] = { '\0' };
+    unsigned char info[128] = { '\0' };
+    unsigned char expected_okm[128] = { '\0' };
+    unsigned char okm[128] = { '\0' };
+    /*
+     * okm_hex is the string representation of okm,
+     * so its size is twice the size of okm, and an extra null-termination.
+     */
+    unsigned char okm_hex[257] = { '\0' };
 
     const mbedtls_md_info_t *md = mbedtls_md_info_from_type( md_alg );
     TEST_ASSERT( md != NULL );
@@ -34,8 +38,8 @@
     TEST_ASSERT( ret == 0 );
 
     // Run hexify on it so that it looks nicer if the assertion fails
-    hexify( okm_string, okm, okm_len );
-    TEST_ASSERT( !strcmp( (char *)okm_string, hex_okm_string ) );
+    hexify( okm_hex, okm, okm_len );
+    TEST_ASSERT( !strcmp( (char *)okm_hex, hex_okm_string ) );
 }
 /* END_CASE */
 
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 8b5f97d..425e93a 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -25,6 +25,9 @@
 Base test mpi_read_write_string #3 (Negative decimal)
 mpi_read_write_string:16:"-23":16:"-23":100:0:0
 
+Base test mpi_read_write_string #4 (Buffer just fits)
+mpi_read_write_string:16:"-4":4:"-10":4:0:0
+
 Test mpi_read_write_string #1 (Invalid character)
 mpi_read_write_string:10:"a28":0:"":100:MBEDTLS_ERR_MPI_INVALID_CHARACTER:0
 
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index d1fa5a4..f982385 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -294,6 +294,8 @@
 
     mbedtls_mpi_init( &X );
 
+    memset( str, '!', sizeof( str ) );
+
     TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == result_read );
     if( result_read == 0 )
     {
@@ -301,6 +303,7 @@
         if( result_write == 0 )
         {
             TEST_ASSERT( strcasecmp( str, input_A ) == 0 );
+            TEST_ASSERT( str[len] == '!' );
         }
     }