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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
from cryptography.exceptions import InvalidTag
_ENCRYPT = 1
_DECRYPT = 0
def _aead_cipher_name(cipher):
from cryptography.hazmat.primitives.ciphers.aead import (
AESCCM,
AESGCM,
ChaCha20Poly1305,
)
if isinstance(cipher, ChaCha20Poly1305):
return b"chacha20-poly1305"
elif isinstance(cipher, AESCCM):
return "aes-{}-ccm".format(len(cipher._key) * 8).encode("ascii")
else:
assert isinstance(cipher, AESGCM)
return "aes-{}-gcm".format(len(cipher._key) * 8).encode("ascii")
def _aead_setup(backend, cipher_name, key, nonce, tag, tag_len, operation):
evp_cipher = backend._lib.EVP_get_cipherbyname(cipher_name)
backend.openssl_assert(evp_cipher != backend._ffi.NULL)
ctx = backend._lib.EVP_CIPHER_CTX_new()
ctx = backend._ffi.gc(ctx, backend._lib.EVP_CIPHER_CTX_free)
res = backend._lib.EVP_CipherInit_ex(
ctx,
evp_cipher,
backend._ffi.NULL,
backend._ffi.NULL,
backend._ffi.NULL,
int(operation == _ENCRYPT),
)
backend.openssl_assert(res != 0)
res = backend._lib.EVP_CIPHER_CTX_set_key_length(ctx, len(key))
backend.openssl_assert(res != 0)
res = backend._lib.EVP_CIPHER_CTX_ctrl(
ctx,
backend._lib.EVP_CTRL_AEAD_SET_IVLEN,
len(nonce),
backend._ffi.NULL,
)
backend.openssl_assert(res != 0)
if operation == _DECRYPT:
res = backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, backend._lib.EVP_CTRL_AEAD_SET_TAG, len(tag), tag
)
backend.openssl_assert(res != 0)
elif cipher_name.endswith(b"-ccm"):
res = backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, backend._lib.EVP_CTRL_AEAD_SET_TAG, tag_len, backend._ffi.NULL
)
backend.openssl_assert(res != 0)
nonce_ptr = backend._ffi.from_buffer(nonce)
key_ptr = backend._ffi.from_buffer(key)
res = backend._lib.EVP_CipherInit_ex(
ctx,
backend._ffi.NULL,
backend._ffi.NULL,
key_ptr,
nonce_ptr,
int(operation == _ENCRYPT),
)
backend.openssl_assert(res != 0)
return ctx
def _set_length(backend, ctx, data_len):
intptr = backend._ffi.new("int *")
res = backend._lib.EVP_CipherUpdate(
ctx, backend._ffi.NULL, intptr, backend._ffi.NULL, data_len
)
backend.openssl_assert(res != 0)
def _process_aad(backend, ctx, associated_data):
outlen = backend._ffi.new("int *")
res = backend._lib.EVP_CipherUpdate(
ctx, backend._ffi.NULL, outlen, associated_data, len(associated_data)
)
backend.openssl_assert(res != 0)
def _process_data(backend, ctx, data):
outlen = backend._ffi.new("int *")
buf = backend._ffi.new("unsigned char[]", len(data))
res = backend._lib.EVP_CipherUpdate(ctx, buf, outlen, data, len(data))
backend.openssl_assert(res != 0)
return backend._ffi.buffer(buf, outlen[0])[:]
def _encrypt(backend, cipher, nonce, data, associated_data, tag_length):
from cryptography.hazmat.primitives.ciphers.aead import AESCCM
cipher_name = _aead_cipher_name(cipher)
ctx = _aead_setup(
backend, cipher_name, cipher._key, nonce, None, tag_length, _ENCRYPT
)
# CCM requires us to pass the length of the data before processing anything
# However calling this with any other AEAD results in an error
if isinstance(cipher, AESCCM):
_set_length(backend, ctx, len(data))
_process_aad(backend, ctx, associated_data)
processed_data = _process_data(backend, ctx, data)
outlen = backend._ffi.new("int *")
res = backend._lib.EVP_CipherFinal_ex(ctx, backend._ffi.NULL, outlen)
backend.openssl_assert(res != 0)
backend.openssl_assert(outlen[0] == 0)
tag_buf = backend._ffi.new("unsigned char[]", tag_length)
res = backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, backend._lib.EVP_CTRL_AEAD_GET_TAG, tag_length, tag_buf
)
backend.openssl_assert(res != 0)
tag = backend._ffi.buffer(tag_buf)[:]
return processed_data + tag
def _decrypt(backend, cipher, nonce, data, associated_data, tag_length):
from cryptography.hazmat.primitives.ciphers.aead import AESCCM
if len(data) < tag_length:
raise InvalidTag
tag = data[-tag_length:]
data = data[:-tag_length]
cipher_name = _aead_cipher_name(cipher)
ctx = _aead_setup(
backend, cipher_name, cipher._key, nonce, tag, tag_length, _DECRYPT
)
# CCM requires us to pass the length of the data before processing anything
# However calling this with any other AEAD results in an error
if isinstance(cipher, AESCCM):
_set_length(backend, ctx, len(data))
_process_aad(backend, ctx, associated_data)
# CCM has a different error path if the tag doesn't match. Errors are
# raised in Update and Final is irrelevant.
if isinstance(cipher, AESCCM):
outlen = backend._ffi.new("int *")
buf = backend._ffi.new("unsigned char[]", len(data))
res = backend._lib.EVP_CipherUpdate(ctx, buf, outlen, data, len(data))
if res != 1:
backend._consume_errors()
raise InvalidTag
processed_data = backend._ffi.buffer(buf, outlen[0])[:]
else:
processed_data = _process_data(backend, ctx, data)
outlen = backend._ffi.new("int *")
res = backend._lib.EVP_CipherFinal_ex(ctx, backend._ffi.NULL, outlen)
if res == 0:
backend._consume_errors()
raise InvalidTag
return processed_data
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