STM32H730, an invalid tag is generated for payloads that are not multiple of 4, as described in Re: STM32U545 AES GCM Tag mismatch - STMicroelectronics Community.
AES-CCM: no issues, everything works.
AES-GCM:
The HAL already handles required padding on its own.
- Encryption and tag generation - work
- Decryption - works
- Tag generation after decryption - invalid
Tried with and without AD. Tried to provide AD and/or Ciphertext as a multiple of 4 and 16 bytes (as suggested by other posts; however, the H7 HAL already handles padding). The resulting tag after decoding is invalid for ciphertext of length that is not a multiple of 4.
Everything works when the ciphertext is multiple of 4 bytes (but not when manually padded to such with 0-oes at the end). The ciphertext of 15 bytes won't generate a correct tag, but it works when it is 12 or 16 bytes.
Standard HAL functions are used: HAL_CRYP_Encrypt, HAL_CRYP_Decrypt, HAL_CRYPEx_AESGCM_GenerateAuthTAG, HAL_CRYP_SetConfig.
What I am doing wrong?
Example
DataType = CRYP_DATATYPE_8B
DataWidthUnit = CRYP_DATAWIDTHUNIT_BYTE
All buffers are aligned (i.e. __attribute__((__aligned__(4)))).
Given
Key (128 bits): [0x071b113b, 0x0ca743fe, 0xcccf3d05, 0x1f737382] (end. adjusted)
IV (12 bytes, providing 16): [0xf0761e8d, 0xcd3d0001, 0x76d457ed, 0x00000002] (end. adjusted, counter set to 2)
Encode, generate tag, decode, generate tag of 15 bytes:
Plaintext (15 bytes) - [0x08, 0x00, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x15, 0x16, 0x17]
Expected
Ciphertext (15 bytes) - [0x13, 0xB4, 0xC7, 0x2B, 0x38, 0x9D, 0xC5, 0x01, 0x8E, 0x72, 0xA1, 0x71, 0xD1, 0x89, 0xA9]
Tag (16 bytes) - [0x8A, 0x0B, 0xF6, 0xE7, 0xC8, 0xAC, 0x33, 0x47, 0x61, 0x16, 0xED, 0xA8, 0x05, 0x2E, 0xF7, 0xC6]
Results
Encryption and tag generation works, getting:
Ciphertext (15 bytes) - [0x13, 0xB4, 0xC7, 0x2B, 0x38, 0x9D, 0xC5, 0x01 0x8E, 0x72, 0xA1, 0x71, 0xD1, 0x89, 0xA9]
Tag (16 bytes) - [0x8A, 0x0B, 0xF6, 0xE7, 0xC8, 0xAC, 0x33, 0x47, 0x61, 0x16, 0xED, 0xA8, 0x05, 0x2E, 0xF7, 0xC6]
Decryption works, but tag generation fails, getting:
Plaintext (15 bytes) - [0x08, 0x00, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x15, 0x16, 0x17]
Tag (16 bytes) - [0x74, 0x27, 0x4E, 0x06, 0x64, 0x84, 0xD8, 0x4C, 0x04, 0x3E, 0x25, 0x38, 0x15, 0x3A, 0x47, 0xA4] - invalid
Encode, generate tag, decode, generate tag of 16 bytes:
Plaintext (16 bytes) - [0x08, 0x00, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x15, 0x16, 0x17, 0xAB]
Expected
Ciphertext (16 bytes) - [0x13, 0xB4, 0xC7, 0x2B, 0x38, 0x9D, 0xC5, 0x01, 0x8E, 0x72, 0xA1, 0x71, 0xD1, 0x89, 0xA9, 0x64]
Tag (16 bytes) - [0x85, 0xE9, 0x98, 0x47, 0xBE, 0x4D, 0xAA, 0xCB, 0x86, 0xFB, 0xCF, 0x00, 0xBE, 0x58, 0x5B, 0x47]
Results
Encryption + tag generation, and decryption + tag generation work as expected.
