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Fixed bad AES PKCS7 block rounding.

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This commit is contained in:
Maarten Billemont 2018-06-03 23:47:16 -04:00
parent 46b609502a
commit 9ee9ab90bd
1 changed files with 7 additions and 7 deletions
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14
src/mpw-util.c
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@ -271,17 +271,17 @@ uint8_t const *mpw_hash_hmac_sha256(const uint8_t *key, const size_t keySize, co
// We do our best to not fail on odd buf's, eg. non-padded cipher texts. // We do our best to not fail on odd buf's, eg. non-padded cipher texts.
static uint8_t const *mpw_aes(bool encrypt, const uint8_t *key, const size_t keySize, const uint8_t *buf, size_t *bufSize) { static uint8_t const *mpw_aes(bool encrypt, const uint8_t *key, const size_t keySize, const uint8_t *buf, size_t *bufSize) {
if (!key || keySize < 16 || !*bufSize) if (!key || keySize < AES_BLOCKLEN || !*bufSize)
return NULL; return NULL;
// IV = zero // IV = zero
uint8_t iv[16]; uint8_t iv[AES_BLOCKLEN];
mpw_zero( iv, sizeof iv ); mpw_zero( iv, sizeof iv );
// Add PKCS#7 padding // Add PKCS#7 padding
uint32_t aesSize = ((uint32_t)*bufSize + 15 / 16) * 16; // round up to block size. uint32_t aesSize = ((uint32_t)*bufSize + AES_BLOCKLEN - 1) & -AES_BLOCKLEN; // round up to block size.
if (encrypt && !(*bufSize % 16)) // add pad block if plain text fits block size. if (encrypt && !(*bufSize % AES_BLOCKLEN)) // add pad block if plain text fits block size.
encrypt += 16; encrypt += AES_BLOCKLEN;
uint8_t aesBuf[aesSize]; uint8_t aesBuf[aesSize];
memcpy( aesBuf, buf, *bufSize ); memcpy( aesBuf, buf, *bufSize );
memset( aesBuf + *bufSize, aesSize - *bufSize, aesSize - *bufSize ); memset( aesBuf + *bufSize, aesSize - *bufSize, aesSize - *bufSize );
@ -292,12 +292,12 @@ static uint8_t const *mpw_aes(bool encrypt, const uint8_t *key, const size_t key
else else
AES_CBC_decrypt_buffer( resultBuf, aesBuf, aesSize, key, iv ); AES_CBC_decrypt_buffer( resultBuf, aesBuf, aesSize, key, iv );
mpw_zero( aesBuf, aesSize ); mpw_zero( aesBuf, aesSize );
mpw_zero( iv, 16 ); mpw_zero( iv, AES_BLOCKLEN );
// Truncate PKCS#7 padding // Truncate PKCS#7 padding
if (encrypt) if (encrypt)
*bufSize = aesSize; *bufSize = aesSize;
else if (*bufSize % 16 == 0 && resultBuf[aesSize - 1] < 16) else if (*bufSize % AES_BLOCKLEN == 0 && resultBuf[aesSize - 1] < AES_BLOCKLEN)
*bufSize -= resultBuf[aesSize - 1]; *bufSize -= resultBuf[aesSize - 1];
return resultBuf; return resultBuf;