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Tweak AES cbc to add pcks7 padding bytes

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This commit is contained in:
Mark Haines 2015-02-25 08:35:53 +00:00
parent 38332e0a12
commit 8df4d9e9b5
4 changed files with 36 additions and 34 deletions
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10
include/axolotl/crypto.hh
View file

@ -42,17 +42,11 @@ struct Aes256Iv {
};
std::size_t aes_pkcs_7_padded_length(
std::size_t aes_encrypt_cbc_length(
std::size_t input_length
);
void aes_pkcs_7_padding(
std::uint8_t const * input, std::size_t input_length,
std::uint8_t * output
);
void aes_encrypt_cbc(
Aes256Key const & key,
Aes256Iv const & iv,
@ -61,7 +55,7 @@ void aes_encrypt_cbc(
);
void aes_decrypt_cbc(
std::size_t aes_decrypt_cbc(
Aes256Key const & key,
Aes256Iv const & iv,
std::uint8_t const * input, std::size_t input_length,

5
include/axolotl/list.hh
View file

@ -15,6 +15,11 @@ public:
T const * begin() const { return _data; }
T const * end() const { return _end; }
/**
* Is the list empty?
*/
bool empty() { return _end == _data; }
/**
* The number of items in the list.
*/

38
src/crypto.cpp
View file

@ -107,26 +107,13 @@ void axolotl::curve25519_shared_secret(
}
std::size_t axolotl::aes_pkcs_7_padded_length(
std::size_t axolotl::aes_encrypt_cbc_length(
std::size_t input_length
) {
return input_length + AES_BLOCK_LENGTH - input_length % AES_BLOCK_LENGTH;
}
void axolotl::aes_pkcs_7_padding(
std::uint8_t const * input, std::size_t input_length,
std::uint8_t * output
) {
std::memcpy(output, input, input_length);
std::size_t padded_length = axolotl::aes_pkcs_7_padded_length(input_length);
std::uint8_t padding = padded_length - input_length;
for (std::size_t i = input_length; i < padded_length; ++i) {
output[i] = padding;
}
}
void axolotl::aes_encrypt_cbc(
axolotl::Aes256Key const & key,
axolotl::Aes256Iv const & iv,
@ -137,17 +124,28 @@ void axolotl::aes_encrypt_cbc(
::aes_key_setup(key.key, key_schedule, 256);
std::uint8_t input_block[AES_BLOCK_LENGTH];
std::memcpy(input_block, iv.iv, AES_BLOCK_LENGTH);
for (std::size_t i = 0; i < input_length; i += AES_BLOCK_LENGTH) {
xor_block<AES_BLOCK_LENGTH>(input_block, &input[i]);
::aes_encrypt(input_block, &output[i], key_schedule, 256);
std::memcpy(input_block, &output[i], AES_BLOCK_LENGTH);
while (input_length >= AES_BLOCK_LENGTH) {
xor_block<AES_BLOCK_LENGTH>(input_block, input);
::aes_encrypt(input_block, output, key_schedule, 256);
std::memcpy(input_block, output, AES_BLOCK_LENGTH);
input += AES_BLOCK_LENGTH;
output += AES_BLOCK_LENGTH;
input_length -= AES_BLOCK_LENGTH;
}
std::size_t i = 0;
for (; i < input_length; ++i) {
input_block[i] ^= input[i];
}
for (; i < AES_BLOCK_LENGTH; ++i) {
input_block[i] ^= AES_BLOCK_LENGTH - input_length;
}
::aes_encrypt(input_block, output, key_schedule, 256);
std::memset(key_schedule, 0, sizeof(key_schedule));
std::memset(input_block, 0, sizeof(AES_BLOCK_LENGTH));
}
void axolotl::aes_decrypt_cbc(
std::size_t axolotl::aes_decrypt_cbc(
axolotl::Aes256Key const & key,
axolotl::Aes256Iv const & iv,
std::uint8_t const * input, std::size_t input_length,
@ -164,6 +162,8 @@ void axolotl::aes_decrypt_cbc(
}
}
std::memset(key_schedule, 0, sizeof(key_schedule));
std::size_t padding = output[input_length - 1];
return (padding > input_length) ? std::size_t(-1) : (input_length - padding);
}

17
tests/test_crypto.cpp
View file

@ -73,24 +73,27 @@ TestCase test_case("AES Test Case 1");
axolotl::Aes256Key key = {};
axolotl::Aes256Iv iv = {};
std::uint8_t input[32] = {};
std::uint8_t input[16] = {};
std::uint8_t expected[32] = {
0xDC, 0x95, 0xC0, 0x78, 0xA2, 0x40, 0x89, 0x89,
0xAD, 0x48, 0xA2, 0x14, 0x92, 0x84, 0x20, 0x87,
0x08, 0xC3, 0x74, 0x84, 0x8C, 0x22, 0x82, 0x33,
0xC2, 0xB3, 0x4F, 0x33, 0x2B, 0xD2, 0xE9, 0xD3
0xF3, 0xC0, 0x03, 0xDD, 0xC4, 0xA7, 0xB8, 0xA9,
0x4B, 0xAE, 0xDF, 0xFC, 0x3D, 0x21, 0x4C, 0x38
};
std::size_t length = axolotl::aes_encrypt_cbc_length(sizeof(input));
assert_equals(std::size_t(32), length);
std::uint8_t actual[32] = {};
axolotl::aes_encrypt_cbc(key, iv, input, sizeof(input), actual);
assert_equals(expected, actual, 32);
axolotl::aes_decrypt_cbc(key, iv, expected, sizeof(expected), actual);
assert_equals(input, actual, 32);
length = axolotl::aes_decrypt_cbc(key, iv, expected, sizeof(expected), actual);
assert_equals(std::size_t(16), length);
assert_equals(input, actual, length);
} /* AES Test Case 1 */