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Compare SQLCipher HMAC values in constant time #264

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Merged
utelle merged 1 commit into from
Sep 11, 2026
Merged

Compare SQLCipher HMAC values in constant time #264

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19 changes: 18 additions & 1 deletion src/cipher_sqlcipher.c
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,23 @@ GetHmacSizeSQLCipherCipher(int algorithm)
return hmacSize;
}

/*
** Compare two HMAC values in constant time, that is, without revealing
** the position of the first differing byte through the execution time.
** Returns 0 if both values are equal, 1 otherwise.
*/
static int
CompareHmacSQLCipherCipher(const unsigned char* hmac1, const unsigned char* hmac2, int len)
{
volatile unsigned char diff = 0;
int j;
for (j = 0; j < len; ++j)
{
diff |= hmac1[j] ^ hmac2[j];
}
return (diff != 0);
}

static int
EncryptPageSQLCipherCipher(void* cipher, int page, unsigned char* data, int len, int reserved)
{
Expand Down Expand Up @@ -482,7 +499,7 @@ DecryptPageSQLCipherCipher(void* cipher, int page, unsigned char* data, int len,
memcpy(pgno_raw, &page, 4);
}
sqlcipher_hmac(sqlCipherCipher->m_hmacAlgorithm, sqlCipherCipher->m_hmacKey, KEYLENGTH_SQLCIPHER, data + offset, n + PAGE_NONCE_LEN_SQLCIPHER - offset, pgno_raw, 4, hmac_out);
hmacOk = (memcmp(data + n + PAGE_NONCE_LEN_SQLCIPHER, hmac_out, hmac_size) == 0);
hmacOk = (CompareHmacSQLCipherCipher(data + n + PAGE_NONCE_LEN_SQLCIPHER, hmac_out, hmac_size) == 0);
}

if (hmacOk != 0)
Expand Down
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