diff --git a/.travis.yml b/.travis.yml
index 4d23652..b4f21a3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,7 +24,8 @@
 - 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 2c031a1..54971ae 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -21,6 +21,15 @@
    * 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.
+   * 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/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 f6e50b9..d142fe6 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -552,15 +552,20 @@
     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 )
     {
@@ -572,7 +577,10 @@
     mbedtls_mpi_init( &T );
 
     if( X->s == -1 )
+    {
         *p++ = '-';
+        buflen--;
+    }
 
     if( radix == 16 )
     {
diff --git a/library/x509.c b/library/x509.c
index 264c7fb..cba6a38 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -1032,8 +1032,8 @@
  */
 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;
@@ -1041,6 +1041,7 @@
     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,
@@ -1050,11 +1051,9 @@
         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 )
@@ -1062,7 +1061,7 @@
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
 
-        return( ret );
+        goto cleanup;
     }
 
     if( verbose != 0 )
@@ -1074,20 +1073,19 @@
         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 7214dc2..8ec6079 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -104,9 +104,9 @@
 
 #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"
@@ -123,17 +123,17 @@
 #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"
 
 /*
@@ -306,7 +306,7 @@
     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;
     }
 
@@ -318,7 +318,7 @@
 
         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/tests/scripts/check-files.py b/tests/scripts/check-files.py
index 7ea321f..0bf0120 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:
@@ -101,77 +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 = [
-            __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)
@@ -196,7 +215,8 @@
             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/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index 343dd78..2518ba5 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -627,6 +627,9 @@
     TEST_ASSERT( memcmp( output, clear, clear_len ) == 0 );
 
     /* then encrypt the clear and make sure we get the same ciphertext and tag */
+    TEST_ASSERT( 0 == mbedtls_cipher_setkey( &ctx, key, 8 * key_len,
+                                             MBEDTLS_ENCRYPT ) );
+
     memset( output, 0xFF, sizeof( output ) );
     outlen = 0;
 
@@ -635,8 +638,8 @@
                                my_tag, tag_len );
     TEST_ASSERT( ret == 0 );
 
-    TEST_ASSERT( outlen == clear_len );
-    TEST_ASSERT( memcmp( output, cipher, clear_len ) == 0 );
+    TEST_ASSERT( outlen == cipher_len );
+    TEST_ASSERT( memcmp( output, cipher, cipher_len ) == 0 );
     TEST_ASSERT( memcmp( my_tag, tag, tag_len ) == 0 );
 
     /* make sure we didn't overwrite */
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 2960641..b8d7ad1 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -19,6 +19,9 @@
 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 04dca0f..aa3c332 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -81,6 +81,8 @@
 
     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 )
     {
@@ -88,6 +90,7 @@
         if( result_write == 0 )
         {
             TEST_ASSERT( strcasecmp( str, input_A ) == 0 );
+            TEST_ASSERT( str[len] == '!' );
         }
     }