diff options
Diffstat (limited to 'docs/hazmat')
| -rw-r--r-- | docs/hazmat/backends/index.rst | 24 | ||||
| -rw-r--r-- | docs/hazmat/backends/interfaces.rst | 11 | ||||
| -rw-r--r-- | docs/hazmat/backends/openssl.rst | 31 | ||||
| -rw-r--r-- | docs/hazmat/primitives/cryptographic-hashes.rst | 3 | ||||
| -rw-r--r-- | docs/hazmat/primitives/hmac.rst | 10 | ||||
| -rw-r--r-- | docs/hazmat/primitives/interfaces.rst | 11 | ||||
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 13 |
7 files changed, 88 insertions, 15 deletions
diff --git a/docs/hazmat/backends/index.rst b/docs/hazmat/backends/index.rst index a89cf0d5..06951281 100644 --- a/docs/hazmat/backends/index.rst +++ b/docs/hazmat/backends/index.rst @@ -1,17 +1,10 @@ .. hazmat:: -Bindings +Backends ======== -.. toctree:: - :maxdepth: 1 - - openssl - interfaces - - -Getting a Backend Provider -~~~~~~~~~~~~~~~~~~~~~~~~~~ +Getting a Backend +----------------- .. currentmodule:: cryptography.hazmat.backends @@ -19,8 +12,7 @@ Getting a Backend Provider the widest number of supported cryptographic algorithms as well as supporting platform specific implementations. -You can get the default backend by calling -:func:`~default_backend`. +You can get the default backend by calling :func:`~default_backend`. The default backend will change over time as we implement new backends and the libraries we use in those backends changes. @@ -32,3 +24,11 @@ the libraries we use in those backends changes. :class:`~interfaces.CipherBackend`, :class:`~interfaces.HashBackend`, and :class:`~interfaces.HMACBackend`. +Individual Backends +------------------- + +.. toctree:: + :maxdepth: 1 + + openssl + interfaces diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst index b524943d..5b6cd64d 100644 --- a/docs/hazmat/backends/interfaces.rst +++ b/docs/hazmat/backends/interfaces.rst @@ -126,6 +126,17 @@ A specific ``backend`` may provide one or more of these interfaces. A backend with methods for using cryptographic hash functions as message authentication codes. + .. method:: hmac_supported(algorithm) + + Check if the specified ``algorithm`` is supported by this backend. + + :param algorithm: An instance of a + :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm` + provider. + + :returns: ``True`` if the specified ``algorithm`` is supported for HMAC + by this backend, otherwise ``False``. + .. method:: create_hmac_ctx(algorithm) Create a diff --git a/docs/hazmat/backends/openssl.rst b/docs/hazmat/backends/openssl.rst index 12fbff04..99b327d9 100644 --- a/docs/hazmat/backends/openssl.rst +++ b/docs/hazmat/backends/openssl.rst @@ -1,7 +1,7 @@ .. hazmat:: -OpenSSL -======= +OpenSSL Backend +=============== These are `CFFI`_ bindings to the `OpenSSL`_ C library. @@ -21,5 +21,32 @@ These are `CFFI`_ bindings to the `OpenSSL`_ C library. and access constants. +Using your own OpenSSL on Linux +------------------------------- + +Python links to OpenSSL for its own purposes and this can sometimes cause +problems when you wish to use a different version of OpenSSL with cryptography. +If you want to use cryptography with your own build of OpenSSL you will need to +make sure that the build is configured correctly so that your version of +OpenSSL doesn't conflict with Python's. + +The options you need to add allow the linker to identify every symbol correctly +even when multiple versions of the library are linked into the same program. If +you are using your distribution's source packages these will probably be +patched in for you already, otherwise you'll need to use options something like +this when configuring OpenSSL:: + + ./config -Wl,--version-script=openssl.ld -Wl,-Bsymbolic-functions -fPIC shared + +You'll also need to generate your own ``openssl.ld`` file. For example:: + + OPENSSL_1.0.1F_CUSTOM { + global: + *; + }; + +You should replace the version string on the first line as appropriate for your +build. + .. _`CFFI`: https://cffi.readthedocs.org/ .. _`OpenSSL`: https://www.openssl.org/ diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst index 90ca198a..38347378 100644 --- a/docs/hazmat/primitives/cryptographic-hashes.rst +++ b/docs/hazmat/primitives/cryptographic-hashes.rst @@ -28,6 +28,9 @@ Message Digests >>> digest.finalize() 'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90' + If the backend doesn't support the requested ``algorithm`` an + :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised. + Keep in mind that attacks against cryptographic hashes only get stronger with time, and that often algorithms that were once thought to be strong, become broken. Because of this it's important to include a plan for diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/hmac.rst index 0c0d0220..b8f94fd2 100644 --- a/docs/hazmat/primitives/hmac.rst +++ b/docs/hazmat/primitives/hmac.rst @@ -34,6 +34,8 @@ message. >>> h.finalize() '#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J' + If the backend doesn't support the requested ``algorithm`` an + :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised. :param key: Secret key as ``bytes``. :param algorithm: A @@ -69,3 +71,11 @@ message. :return bytes: The message digest as bytes. :raises cryptography.exceptions.AlreadyFinalized: + + .. method:: verify(signature) + + Finalize the current context and securely compare digest to ``signature``. + + :param bytes signature: The bytes of the HMAC signature recieved. + :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize` + :raises cryptography.exceptions.InvalidSignature: If signature does not match digest diff --git a/docs/hazmat/primitives/interfaces.rst b/docs/hazmat/primitives/interfaces.rst index e798c0e6..edb24cd9 100644 --- a/docs/hazmat/primitives/interfaces.rst +++ b/docs/hazmat/primitives/interfaces.rst @@ -36,6 +36,17 @@ Symmetric Ciphers The number of bits in the key being used. +.. class:: BlockCipherAlgorithm + + A block cipher algorithm. + + .. attribute:: block_size + + :type: int + + The number of bits in a block. + + Cipher Modes ------------ diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index f4d0457a..30896a05 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -61,7 +61,7 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. provider. If the backend doesn't support the requested combination of ``cipher`` - and ``mode`` an :class:`cryptography.exceptions.UnsupportedAlgorithm` + and ``mode`` an :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised. .. method:: decryptor() @@ -352,6 +352,16 @@ Modes Do not reuse an ``initialization_vector`` with a given ``key``. + .. note:: + + Cryptography will emit a 128-bit tag when finalizing encryption. + You can shorten a tag by truncating it to the desired length, but this + is **not recommended** as it lowers the security margins of the + authentication (`NIST SP-800-38D`_ recommends 96-bits or greater). + If you must shorten the tag the minimum allowed length is 4 bytes + (32-bits). Applications **must** verify the tag is the expected length + to guarantee the expected security margin. + :param bytes tag: The tag bytes to verify during decryption. When encrypting this must be None. @@ -390,3 +400,4 @@ Insecure Modes .. _`described by Colin Percival`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html .. _`recommends 96-bit IV length`: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf +.. _`NIST SP-800-38D`: http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf |