diff --git a/.travis.yml b/.travis.yml
index 39ae19c..cdb68ac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,7 @@
-language: c
-compiler: gcc
+# Declare python as our language. This way we get our chosen Python version,
+# and pip is available. Gcc and clang are available anyway.
+language: python
+python: 3.5
 sudo: false
 cache: ccache
 
@@ -16,10 +18,6 @@
           - libnewlib-arm-none-eabi
           - gcc-arm-linux-gnueabi
           - libc6-dev-armel-cross
-      language: python # Needed to get pip for Python 3
-      python: 3.5 # version from Ubuntu 16.04
-      install:
-        - pip install mypy==0.780 pylint==2.4.4
       script:
         - tests/scripts/all.sh -k 'check_*'
         - tests/scripts/all.sh -k test_default_out_of_box
@@ -32,11 +30,16 @@
 
     - name: Windows
       os: windows
+      # The language 'python' is currently unsupported on the
+      # Windows Build Environment. And 'generic' causes the job to get stuck
+      # on "Booting virtual machine".
+      language: c
       before_install:
         - choco install python --version=3.5.4
       env:
         # Add the directory where the Choco packages go
         - PATH=/c/Python35:/c/Python35/Scripts:$PATH
+        - PYTHON=python.exe
       script:
         - type perl; perl --version
         - type python; python --version
@@ -53,6 +56,9 @@
     - SEED=1
     - secure: "FrI5d2s+ckckC17T66c8jm2jV6i2DkBPU5nyWzwbedjmEBeocREfQLd/x8yKpPzLDz7ghOvr+/GQvsPPn0dVkGlNzm3Q+hGHc/ujnASuUtGrcuMM+0ALnJ3k4rFr9xEvjJeWb4SmhJO5UCAZYvTItW4k7+bj9L+R6lt3TzQbXzg="
 
+install:
+  - $PYTHON scripts/min_requirements.py
+
 addons:
   apt:
     packages:
diff --git a/ChangeLog.d/additional_cipher_info_getters.txt b/ChangeLog.d/additional_cipher_info_getters.txt
new file mode 100644
index 0000000..5cb1ad6
--- /dev/null
+++ b/ChangeLog.d/additional_cipher_info_getters.txt
@@ -0,0 +1,3 @@
+Features
+   * Add functions to get the IV and block size from cipher_info structs.
+   * Add functions to check if a cipher supports variable IV or key size.
diff --git a/README.md b/README.md
index c8d9450..ea1d7a3 100644
--- a/README.md
+++ b/README.md
@@ -59,7 +59,10 @@
 The following tools are required:
 
 * Perl, for some library source files and for Visual Studio build files.
-* Python 3, for some sample programs and test data.
+* Python 3 and some Python packages, for some library source files, sample programs and test data. To install the necessary packages, run
+    ```
+    python -m pip install -r scripts/basic.requirements.txt
+    ```
 * A C compiler for the host platform, for some test data.
 
 If you are cross-compiling, you must set the `CC` environment variable to a C compiler for the host platform when generating the configuration-independent files.
diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 892771e..c04097d 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -508,6 +508,80 @@
 }
 
 /**
+ * \brief       This function returns the size of the IV or nonce
+ *              for the cipher info structure, in bytes.
+ *
+ * \param info  The cipher info structure. This may be \c NULL.
+ *
+ * \return      The recommended IV size.
+ * \return      \c 0 for ciphers not using an IV or a nonce.
+ * \return      \c 0 if \p info is \c NULL.
+ */
+static inline size_t mbedtls_cipher_info_get_iv_size(
+    const mbedtls_cipher_info_t *info )
+{
+    if( info == NULL )
+        return( 0 );
+
+    return( (size_t) info->MBEDTLS_PRIVATE(iv_size) );
+}
+
+/**
+ * \brief        This function returns the block size of the given
+ *               cipher info structure in bytes.
+ *
+ * \param info   The cipher info structure. This may be \c NULL.
+ *
+ * \return       The block size of the cipher.
+ * \return       \c 1 if the cipher is a stream cipher.
+ * \return       \c 0 if \p info is \c NULL.
+ */
+static inline size_t mbedtls_cipher_info_get_block_size(
+    const mbedtls_cipher_info_t *info )
+{
+    if( info == NULL )
+        return( 0 );
+
+    return( (size_t) info->MBEDTLS_PRIVATE(block_size) );
+}
+
+/**
+ * \brief        This function returns a non-zero value if the key length for
+ *               the given cipher is variable.
+ *
+ * \param info   The cipher info structure. This may be \c NULL.
+ *
+ * \return       Non-zero if the key length is variable, \c 0 otherwise.
+ * \return       \c 0 if the given pointer is \c NULL.
+ */
+static inline int mbedtls_cipher_info_has_variable_key_bitlen(
+    const mbedtls_cipher_info_t *info )
+{
+    if( info == NULL )
+        return( 0 );
+
+    return( info->MBEDTLS_PRIVATE(flags) & MBEDTLS_CIPHER_VARIABLE_KEY_LEN );
+}
+
+/**
+ * \brief        This function returns a non-zero value if the IV size for
+ *               the given cipher is variable.
+ *
+ * \param info   The cipher info structure. This may be \c NULL.
+ *
+ * \return       Non-zero if the IV size is variable, \c 0 otherwise.
+ * \return       \c 0 if the given pointer is \c NULL.
+ */
+static inline int mbedtls_cipher_info_has_variable_iv_size(
+    const mbedtls_cipher_info_t *info )
+{
+    if( info == NULL )
+        return( 0 );
+
+    return( info->MBEDTLS_PRIVATE(flags) & MBEDTLS_CIPHER_VARIABLE_IV_LEN );
+}
+
+/**
  * \brief               This function initializes a \p cipher_context as NONE.
  *
  * \param ctx           The context to be initialized. This must not be \c NULL.
@@ -583,11 +657,13 @@
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 /**
- * \brief        This function returns the block size of the given cipher.
+ * \brief        This function returns the block size of the given cipher
+ *               in bytes.
  *
- * \param ctx    The context of the cipher. This must be initialized.
+ * \param ctx    The context of the cipher.
  *
  * \return       The block size of the underlying cipher.
+ * \return       \c 1 if the cipher is a stream cipher.
  * \return       \c 0 if \p ctx has not been initialized.
  */
 static inline unsigned int mbedtls_cipher_get_block_size(
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index ee4b54c..1643b2e 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -153,10 +153,10 @@
  * the owner of a key.
  *
  * \param[out] attributes  The attribute structure to write to.
- * \param owner_id         The key owner identifier.
+ * \param owner            The key owner identifier.
  */
 static void mbedtls_set_key_owner_id( psa_key_attributes_t *attributes,
-                                      mbedtls_key_owner_id_t owner_id );
+                                      mbedtls_key_owner_id_t owner );
 #endif
 
 /** Set the location of a persistent key.
diff --git a/scripts/basic.requirements.txt b/scripts/basic.requirements.txt
new file mode 100644
index 0000000..1be3d0c
--- /dev/null
+++ b/scripts/basic.requirements.txt
@@ -0,0 +1,5 @@
+# Python modules required to build Mbed TLS in ordinary conditions.
+
+# Required to (re-)generate source files. Not needed if the generated source
+# files are already present and up-to-date.
+-r driver.requirements.txt
diff --git a/scripts/ci.requirements.txt b/scripts/ci.requirements.txt
new file mode 100644
index 0000000..209ae3d
--- /dev/null
+++ b/scripts/ci.requirements.txt
@@ -0,0 +1,12 @@
+# Python package requirements for Mbed TLS testing.
+
+-r driver.requirements.txt
+
+# Use a known version of Pylint, because new versions tend to add warnings
+# that could start rejecting our code.
+# 2.4.4 is the version in Ubuntu 20.04. It supports Python >=3.5.
+pylint == 2.4.4
+
+# Use the earliest version of mypy that works with our code base.
+# See https://github.com/ARMmbed/mbedtls/pull/3953 .
+mypy >= 0.780
diff --git a/scripts/driver.requirements.txt b/scripts/driver.requirements.txt
new file mode 100644
index 0000000..17569bb
--- /dev/null
+++ b/scripts/driver.requirements.txt
@@ -0,0 +1,10 @@
+# Python package requirements for driver implementers.
+
+# Use the version of Jinja that's in Ubuntu 20.04.
+# See https://github.com/ARMmbed/mbedtls/pull/5067#discussion_r738794607 .
+# Note that Jinja 3.0 drops support for Python 3.5, so we need to support
+# Jinja 2.x as long as we're still using Python 3.5 anywhere.
+Jinja2 >= 2.10.1
+# Jinja2 >=2.10, <<3.0 needs a separate package for type annotations
+types-Jinja2
+
diff --git a/scripts/maintainer.requirements.txt b/scripts/maintainer.requirements.txt
new file mode 100644
index 0000000..b149921
--- /dev/null
+++ b/scripts/maintainer.requirements.txt
@@ -0,0 +1,10 @@
+# Python packages that are only useful to Mbed TLS maintainers.
+
+-r ci.requirements.txt
+
+# For source code analyses
+clang
+
+# For building some test vectors
+pycryptodomex
+pycryptodome-test-vectors
diff --git a/scripts/min_requirements.py b/scripts/min_requirements.py
new file mode 100755
index 0000000..eecab1c
--- /dev/null
+++ b/scripts/min_requirements.py
@@ -0,0 +1,138 @@
+#!/usr/bin/env python3
+"""Install all the required Python packages, with the minimum Python version.
+"""
+
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import os
+import re
+import subprocess
+import sys
+import tempfile
+import typing
+
+from typing import List, Optional
+from mbedtls_dev import typing_util
+
+def pylint_doesn_t_notice_that_certain_types_are_used_in_annotations(
+        _list: List[typing.Any],
+) -> None:
+    pass
+
+
+class Requirements:
+    """Collect and massage Python requirements."""
+
+    def __init__(self) -> None:
+        self.requirements = [] #type: List[str]
+
+    def adjust_requirement(self, req: str) -> str:
+        """Adjust a requirement to the minimum specified version."""
+        # allow inheritance #pylint: disable=no-self-use
+        # If a requirement specifies a minimum version, impose that version.
+        req = re.sub(r'>=|~=', r'==', req)
+        return req
+
+    def add_file(self, filename: str) -> None:
+        """Add requirements from the specified file.
+
+        This method supports a subset of pip's requirement file syntax:
+        * One requirement specifier per line, which is passed to
+          `adjust_requirement`.
+        * Comments (``#`` at the beginning of the line or after whitespace).
+        * ``-r FILENAME`` to include another file.
+        """
+        for line in open(filename):
+            line = line.strip()
+            line = re.sub(r'(\A|\s+)#.*', r'', line)
+            if not line:
+                continue
+            m = re.match(r'-r\s+', line)
+            if m:
+                nested_file = os.path.join(os.path.dirname(filename),
+                                           line[m.end(0):])
+                self.add_file(nested_file)
+                continue
+            self.requirements.append(self.adjust_requirement(line))
+
+    def write(self, out: typing_util.Writable) -> None:
+        """List the gathered requirements."""
+        for req in self.requirements:
+            out.write(req + '\n')
+
+    def install(
+            self,
+            pip_general_options: Optional[List[str]] = None,
+            pip_install_options: Optional[List[str]] = None,
+    ) -> None:
+        """Call pip to install the requirements."""
+        if pip_general_options is None:
+            pip_general_options = []
+        if pip_install_options is None:
+            pip_install_options = []
+        with tempfile.TemporaryDirectory() as temp_dir:
+            # This is more complicated than it needs to be for the sake
+            # of Windows. Use a temporary file rather than the command line
+            # to avoid quoting issues. Use a temporary directory rather
+            # than NamedTemporaryFile because with a NamedTemporaryFile on
+            # Windows, the subprocess can't open the file because this process
+            # has an exclusive lock on it.
+            req_file_name = os.path.join(temp_dir, 'requirements.txt')
+            with open(req_file_name, 'w') as req_file:
+                self.write(req_file)
+            subprocess.check_call([sys.executable, '-m', 'pip'] +
+                                  pip_general_options +
+                                  ['install'] + pip_install_options +
+                                  ['-r', req_file_name])
+
+DEFAULT_REQUIREMENTS_FILE = 'ci.requirements.txt'
+
+def main() -> None:
+    """Command line entry point."""
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--no-act', '-n',
+                        action='store_true',
+                        help="Don't act, just print what will be done")
+    parser.add_argument('--pip-install-option',
+                        action='append', dest='pip_install_options',
+                        help="Pass this option to pip install")
+    parser.add_argument('--pip-option',
+                        action='append', dest='pip_general_options',
+                        help="Pass this general option to pip")
+    parser.add_argument('--user',
+                        action='append_const', dest='pip_install_options',
+                        const='--user',
+                        help="Install to the Python user install directory"
+                             " (short for --pip-install-option --user)")
+    parser.add_argument('files', nargs='*', metavar='FILE',
+                        help="Requirement files"
+                             " (default: {} in the script's directory)" \
+                             .format(DEFAULT_REQUIREMENTS_FILE))
+    options = parser.parse_args()
+    if not options.files:
+        options.files = [os.path.join(os.path.dirname(__file__),
+                                      DEFAULT_REQUIREMENTS_FILE)]
+    reqs = Requirements()
+    for filename in options.files:
+        reqs.add_file(filename)
+    reqs.write(sys.stdout)
+    if not options.no_act:
+        reqs.install(pip_general_options=options.pip_general_options,
+                     pip_install_options=options.pip_install_options)
+
+if __name__ == '__main__':
+    main()
diff --git a/tests/docker/bionic/Dockerfile b/tests/docker/bionic/Dockerfile
index 41789c6..50f5a7f 100644
--- a/tests/docker/bionic/Dockerfile
+++ b/tests/docker/bionic/Dockerfile
@@ -160,7 +160,3 @@
 
 ENV GNUTLS_NEXT_CLI=/usr/local/gnutls-3.7.2/bin/gnutls-cli
 ENV GNUTLS_NEXT_SERV=/usr/local/gnutls-3.7.2/bin/gnutls-serv
-
-RUN pip3 install --no-cache-dir \
-    mbed-host-tests \
-    mock
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index e496856..2efc434 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -18,7 +18,7 @@
 static int check_cipher_info( mbedtls_cipher_type_t type,
                               const mbedtls_cipher_info_t *info )
 {
-    size_t key_bitlen;
+    size_t key_bitlen, block_size, iv_size;
 
     TEST_ASSERT( info != NULL );
     TEST_EQUAL( type, mbedtls_cipher_info_get_type( info ) );
@@ -33,8 +33,14 @@
     TEST_ASSERT( mbedtls_cipher_info_from_string( info->name ) == info );
 
     key_bitlen = mbedtls_cipher_info_get_key_bitlen( info );
+    block_size = mbedtls_cipher_info_get_block_size( info );
+    iv_size = mbedtls_cipher_info_get_iv_size( info );
     if( info->type == MBEDTLS_CIPHER_NULL )
+    {
         TEST_ASSERT( key_bitlen == 0 );
+        TEST_ASSERT( block_size == 1 );
+        TEST_ASSERT( iv_size == 0 );
+    }
     else if( info->mode == MBEDTLS_MODE_XTS )
     {
         TEST_ASSERT( key_bitlen == 256 ||
@@ -44,14 +50,28 @@
     else if( ! strncmp( info->name, "DES-EDE3-", 9 ) )
     {
         TEST_ASSERT( key_bitlen == 192 );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_key_bitlen( info ) );
+        TEST_ASSERT( block_size == 8 );
     }
     else if( ! strncmp( info->name, "DES-EDE-", 8 ) )
     {
         TEST_ASSERT( key_bitlen == 128 );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_key_bitlen( info ) );
+        TEST_ASSERT( block_size == 8 );
     }
     else if( ! strncmp( info->name, "DES-", 4 ) )
     {
         TEST_ASSERT( key_bitlen == 64 );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_key_bitlen( info ) );
+        TEST_ASSERT( block_size == 8 );
+    }
+    else if( ! strncmp( info->name, "AES", 3 ) )
+    {
+        TEST_ASSERT( key_bitlen == 128 ||
+                     key_bitlen == 192 ||
+                     key_bitlen == 256 );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_key_bitlen( info ) );
+        TEST_ASSERT( block_size == 16 );
     }
     else
     {
@@ -60,6 +80,23 @@
                      key_bitlen == 256 );
     }
 
+    if( strstr( info->name, "-ECB" ) != NULL )
+    {
+        TEST_ASSERT( iv_size == 0 );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_iv_size( info ) );
+    }
+    else if( strstr( info->name, "-CBC" ) != NULL ||
+             strstr( info->name, "-CTR" ) != NULL )
+    {
+        TEST_ASSERT( iv_size == block_size );
+        TEST_ASSERT( ! mbedtls_cipher_info_has_variable_iv_size( info ) );
+    }
+    else if( strstr( info->name, "-GCM" ) != NULL )
+    {
+        TEST_ASSERT( iv_size == block_size - 4 );
+        TEST_ASSERT( mbedtls_cipher_info_has_variable_iv_size( info ) );
+    }
+
     return( 1 );
 
 exit: