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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 annotations
import typing
from cryptography.exceptions import InvalidTag
if typing.TYPE_CHECKING:
from cryptography.hazmat.backends.openssl.backend import Backend
from cryptography.hazmat.primitives.ciphers.aead import (
AESCCM,
AESGCM,
AESOCB3,
AESSIV,
ChaCha20Poly1305,
)
_AEADTypes = typing.Union[
AESCCM, AESGCM, AESOCB3, AESSIV, ChaCha20Poly1305
]
def _is_evp_aead_supported_cipher(
backend: Backend, cipher: _AEADTypes
) -> bool:
"""
Checks whether the given cipher is supported through
EVP_AEAD rather than the normal OpenSSL EVP_CIPHER API.
"""
from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
return backend._lib.Cryptography_HAS_EVP_AEAD and isinstance(
cipher, ChaCha20Poly1305
)
def _aead_cipher_supported(backend: Backend, cipher: _AEADTypes) -> bool:
if _is_evp_aead_supported_cipher(backend, cipher):
return True
else:
cipher_name = _evp_cipher_cipher_name(cipher)
if backend._fips_enabled and cipher_name not in backend._fips_aead:
return False
# SIV isn't loaded through get_cipherbyname but instead a new fetch API
# only available in 3.0+. But if we know we're on 3.0+ then we know
# it's supported.
if cipher_name.endswith(b"-siv"):
return backend._lib.CRYPTOGRAPHY_OPENSSL_300_OR_GREATER == 1
else:
return (
backend._lib.EVP_get_cipherbyname(cipher_name)
!= backend._ffi.NULL
)
def _aead_create_ctx(
backend: Backend,
cipher: _AEADTypes,
key: bytes,
):
if _is_evp_aead_supported_cipher(backend, cipher):
return _evp_aead_create_ctx(backend, cipher, key)
else:
return _evp_cipher_create_ctx(backend, cipher, key)
def _encrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any = None,
) -> bytes:
if _is_evp_aead_supported_cipher(backend, cipher):
return _evp_aead_encrypt(
backend, cipher, nonce, data, associated_data, tag_length, ctx
)
else:
return _evp_cipher_encrypt(
backend, cipher, nonce, data, associated_data, tag_length, ctx
)
def _decrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any = None,
) -> bytes:
if _is_evp_aead_supported_cipher(backend, cipher):
return _evp_aead_decrypt(
backend, cipher, nonce, data, associated_data, tag_length, ctx
)
else:
return _evp_cipher_decrypt(
backend, cipher, nonce, data, associated_data, tag_length, ctx
)
def _evp_aead_create_ctx(
backend: Backend,
cipher: _AEADTypes,
key: bytes,
tag_len: typing.Optional[int] = None,
):
aead_cipher = _evp_aead_get_cipher(backend, cipher)
assert aead_cipher is not None
key_ptr = backend._ffi.from_buffer(key)
tag_len = (
backend._lib.EVP_AEAD_DEFAULT_TAG_LENGTH
if tag_len is None
else tag_len
)
ctx = backend._lib.Cryptography_EVP_AEAD_CTX_new(
aead_cipher, key_ptr, len(key), tag_len
)
backend.openssl_assert(ctx != backend._ffi.NULL)
ctx = backend._ffi.gc(ctx, backend._lib.EVP_AEAD_CTX_free)
return ctx
def _evp_aead_get_cipher(backend: Backend, cipher: _AEADTypes):
from cryptography.hazmat.primitives.ciphers.aead import (
ChaCha20Poly1305,
)
# Currently only ChaCha20-Poly1305 is supported using this API
assert isinstance(cipher, ChaCha20Poly1305)
return backend._lib.EVP_aead_chacha20_poly1305()
def _evp_aead_encrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any,
) -> bytes:
assert ctx is not None
aead_cipher = _evp_aead_get_cipher(backend, cipher)
assert aead_cipher is not None
out_len = backend._ffi.new("size_t *")
# max_out_len should be in_len plus the result of
# EVP_AEAD_max_overhead.
max_out_len = len(data) + backend._lib.EVP_AEAD_max_overhead(aead_cipher)
out_buf = backend._ffi.new("uint8_t[]", max_out_len)
data_ptr = backend._ffi.from_buffer(data)
nonce_ptr = backend._ffi.from_buffer(nonce)
aad = b"".join(associated_data)
aad_ptr = backend._ffi.from_buffer(aad)
res = backend._lib.EVP_AEAD_CTX_seal(
ctx,
out_buf,
out_len,
max_out_len,
nonce_ptr,
len(nonce),
data_ptr,
len(data),
aad_ptr,
len(aad),
)
backend.openssl_assert(res == 1)
encrypted_data = backend._ffi.buffer(out_buf, out_len[0])[:]
return encrypted_data
def _evp_aead_decrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any,
) -> bytes:
if len(data) < tag_length:
raise InvalidTag
assert ctx is not None
out_len = backend._ffi.new("size_t *")
# max_out_len should at least in_len
max_out_len = len(data)
out_buf = backend._ffi.new("uint8_t[]", max_out_len)
data_ptr = backend._ffi.from_buffer(data)
nonce_ptr = backend._ffi.from_buffer(nonce)
aad = b"".join(associated_data)
aad_ptr = backend._ffi.from_buffer(aad)
res = backend._lib.EVP_AEAD_CTX_open(
ctx,
out_buf,
out_len,
max_out_len,
nonce_ptr,
len(nonce),
data_ptr,
len(data),
aad_ptr,
len(aad),
)
if res == 0:
backend._consume_errors()
raise InvalidTag
decrypted_data = backend._ffi.buffer(out_buf, out_len[0])[:]
return decrypted_data
_ENCRYPT = 1
_DECRYPT = 0
def _evp_cipher_cipher_name(cipher: _AEADTypes) -> bytes:
from cryptography.hazmat.primitives.ciphers.aead import (
AESCCM,
AESGCM,
AESOCB3,
AESSIV,
ChaCha20Poly1305,
)
if isinstance(cipher, ChaCha20Poly1305):
return b"chacha20-poly1305"
elif isinstance(cipher, AESCCM):
return f"aes-{len(cipher._key) * 8}-ccm".encode("ascii")
elif isinstance(cipher, AESOCB3):
return f"aes-{len(cipher._key) * 8}-ocb".encode("ascii")
elif isinstance(cipher, AESSIV):
return f"aes-{len(cipher._key) * 8 // 2}-siv".encode("ascii")
else:
assert isinstance(cipher, AESGCM)
return f"aes-{len(cipher._key) * 8}-gcm".encode("ascii")
def _evp_cipher(cipher_name: bytes, backend: Backend):
if cipher_name.endswith(b"-siv"):
evp_cipher = backend._lib.EVP_CIPHER_fetch(
backend._ffi.NULL,
cipher_name,
backend._ffi.NULL,
)
backend.openssl_assert(evp_cipher != backend._ffi.NULL)
evp_cipher = backend._ffi.gc(evp_cipher, backend._lib.EVP_CIPHER_free)
else:
evp_cipher = backend._lib.EVP_get_cipherbyname(cipher_name)
backend.openssl_assert(evp_cipher != backend._ffi.NULL)
return evp_cipher
def _evp_cipher_create_ctx(
backend: Backend,
cipher: _AEADTypes,
key: bytes,
):
ctx = backend._lib.EVP_CIPHER_CTX_new()
backend.openssl_assert(ctx != backend._ffi.NULL)
ctx = backend._ffi.gc(ctx, backend._lib.EVP_CIPHER_CTX_free)
cipher_name = _evp_cipher_cipher_name(cipher)
evp_cipher = _evp_cipher(cipher_name, backend)
key_ptr = backend._ffi.from_buffer(key)
res = backend._lib.EVP_CipherInit_ex(
ctx,
evp_cipher,
backend._ffi.NULL,
key_ptr,
backend._ffi.NULL,
0,
)
backend.openssl_assert(res != 0)
return ctx
def _evp_cipher_aead_setup(
backend: Backend,
cipher_name: bytes,
key: bytes,
nonce: bytes,
tag: typing.Optional[bytes],
tag_len: int,
operation: int,
):
evp_cipher = _evp_cipher(cipher_name, backend)
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)
# CCM requires the IVLEN to be set before calling SET_TAG on decrypt
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:
assert tag is not None
_evp_cipher_set_tag(backend, ctx, tag)
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 _evp_cipher_set_tag(backend, ctx, tag: bytes) -> None:
tag_ptr = backend._ffi.from_buffer(tag)
res = backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, backend._lib.EVP_CTRL_AEAD_SET_TAG, len(tag), tag_ptr
)
backend.openssl_assert(res != 0)
def _evp_cipher_set_nonce_operation(
backend, ctx, nonce: bytes, operation: int
) -> None:
nonce_ptr = backend._ffi.from_buffer(nonce)
res = backend._lib.EVP_CipherInit_ex(
ctx,
backend._ffi.NULL,
backend._ffi.NULL,
backend._ffi.NULL,
nonce_ptr,
int(operation == _ENCRYPT),
)
backend.openssl_assert(res != 0)
def _evp_cipher_set_length(backend: Backend, ctx, data_len: int) -> None:
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 _evp_cipher_process_aad(
backend: Backend, ctx, associated_data: bytes
) -> None:
outlen = backend._ffi.new("int *")
a_data_ptr = backend._ffi.from_buffer(associated_data)
res = backend._lib.EVP_CipherUpdate(
ctx, backend._ffi.NULL, outlen, a_data_ptr, len(associated_data)
)
backend.openssl_assert(res != 0)
def _evp_cipher_process_data(backend: Backend, ctx, data: bytes) -> bytes:
outlen = backend._ffi.new("int *")
buf = backend._ffi.new("unsigned char[]", len(data))
data_ptr = backend._ffi.from_buffer(data)
res = backend._lib.EVP_CipherUpdate(ctx, buf, outlen, data_ptr, len(data))
if res == 0:
# AES SIV can error here if the data is invalid on decrypt
backend._consume_errors()
raise InvalidTag
return backend._ffi.buffer(buf, outlen[0])[:]
def _evp_cipher_encrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any = None,
) -> bytes:
from cryptography.hazmat.primitives.ciphers.aead import AESCCM, AESSIV
if ctx is None:
cipher_name = _evp_cipher_cipher_name(cipher)
ctx = _evp_cipher_aead_setup(
backend,
cipher_name,
cipher._key,
nonce,
None,
tag_length,
_ENCRYPT,
)
else:
_evp_cipher_set_nonce_operation(backend, ctx, nonce, _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):
_evp_cipher_set_length(backend, ctx, len(data))
for ad in associated_data:
_evp_cipher_process_aad(backend, ctx, ad)
processed_data = _evp_cipher_process_data(backend, ctx, data)
outlen = backend._ffi.new("int *")
# All AEADs we support besides OCB are streaming so they return nothing
# in finalization. OCB can return up to (16 byte block - 1) bytes so
# we need a buffer here too.
buf = backend._ffi.new("unsigned char[]", 16)
res = backend._lib.EVP_CipherFinal_ex(ctx, buf, outlen)
backend.openssl_assert(res != 0)
processed_data += backend._ffi.buffer(buf, outlen[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)[:]
if isinstance(cipher, AESSIV):
# RFC 5297 defines the output as IV || C, where the tag we generate
# is the "IV" and C is the ciphertext. This is the opposite of our
# other AEADs, which are Ciphertext || Tag
backend.openssl_assert(len(tag) == 16)
return tag + processed_data
else:
return processed_data + tag
def _evp_cipher_decrypt(
backend: Backend,
cipher: _AEADTypes,
nonce: bytes,
data: bytes,
associated_data: typing.List[bytes],
tag_length: int,
ctx: typing.Any = None,
) -> bytes:
from cryptography.hazmat.primitives.ciphers.aead import AESCCM, AESSIV
if len(data) < tag_length:
raise InvalidTag
if isinstance(cipher, AESSIV):
# RFC 5297 defines the output as IV || C, where the tag we generate
# is the "IV" and C is the ciphertext. This is the opposite of our
# other AEADs, which are Ciphertext || Tag
tag = data[:tag_length]
data = data[tag_length:]
else:
tag = data[-tag_length:]
data = data[:-tag_length]
if ctx is None:
cipher_name = _evp_cipher_cipher_name(cipher)
ctx = _evp_cipher_aead_setup(
backend,
cipher_name,
cipher._key,
nonce,
tag,
tag_length,
_DECRYPT,
)
else:
_evp_cipher_set_nonce_operation(backend, ctx, nonce, _DECRYPT)
_evp_cipher_set_tag(backend, ctx, tag)
# 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):
_evp_cipher_set_length(backend, ctx, len(data))
for ad in associated_data:
_evp_cipher_process_aad(backend, ctx, ad)
# 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))
d_ptr = backend._ffi.from_buffer(data)
res = backend._lib.EVP_CipherUpdate(ctx, buf, outlen, d_ptr, len(data))
if res != 1:
backend._consume_errors()
raise InvalidTag
processed_data = backend._ffi.buffer(buf, outlen[0])[:]
else:
processed_data = _evp_cipher_process_data(backend, ctx, data)
outlen = backend._ffi.new("int *")
# OCB can return up to 15 bytes (16 byte block - 1) in finalization
buf = backend._ffi.new("unsigned char[]", 16)
res = backend._lib.EVP_CipherFinal_ex(ctx, buf, outlen)
processed_data += backend._ffi.buffer(buf, outlen[0])[:]
if res == 0:
backend._consume_errors()
raise InvalidTag
return processed_data
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