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STM32L486: Trouble decrypting AES-256 ECB data but OK with encrypting??

Question asked by Jennifer D on Jul 21, 2017
Latest reply on Aug 31, 2017 by Jennifer D

Hi all :

I am using the STM32L4xx Stm Cube drivers for AES-256 ECB encryption on the STM32L486. Although the encrypted data comes out perfectly, the decrypted encrypted data is not the original plaintext. To be clear: I am not using the X crypto library, but instead the stm32l4xx_cryp and stm32l4xx_cryp_ex modules that are included in the from the STM Cube STM32L4xx HAL Drivers. 


Some info about the code: 

-The MX_AES_Init function uses HAL_CRYP_Init to initialize the AES module 

- I am using this API to encrypt and decrypt data:  HAL_CRYP_AESECB_Encrypt_IT

-After the encryption, I deinit the AES module change the operating mode to decrypt and re init using the HAL init function 

- I tried setting the original operating mode to decrypt and feeding in the encrypted output, but I get the same incorrect decrypted data instead of the original plaintext I added . 


When I try to decrypt the cipher_text array back to the plain_text array it doesn't work, but the encrypted data is correct according to an AES-256 calculator I used


uint8_t plain_text[64] =
0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96,
0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c,
0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11,
0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17,
0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10


uint8_t Key[32] =
0x60, 0x3d, 0xeb, 0x10, 0x15, 0xca, 0x71, 0xbe,
0x2b, 0x73, 0xae, 0xf0, 0x85, 0x7d, 0x77, 0x81,
0x1f, 0x35, 0x2c, 0x07, 0x3b, 0x61, 0x08, 0xd7,
0x2d, 0x98, 0x10, 0xa3, 0x09, 0x14, 0xdf, 0xf4,


const uint8_t ciphertext[64] =
0xf3, 0xee, 0xd1, 0xbd, 0xb5, 0xd2, 0xa0, 0x3c,
0x06, 0x4b, 0x5a, 0x7e, 0x3d, 0xb1, 0x81, 0xf8,
0x59, 0x1c, 0xcb, 0x10, 0xd4, 0x10, 0xed, 0x26,
0xdc, 0x5b, 0xa7, 0x4a, 0x31, 0x36, 0x28, 0x70,
0xb6, 0xed, 0x21, 0xb9, 0x9c, 0xa6, 0xf4, 0xf9,
0xf1, 0x53, 0xe7, 0xb1, 0xbe, 0xaf, 0xed, 0x1d,
0x23, 0x30, 0x4b, 0x7a, 0x39, 0xf9, 0xf3, 0xff,
0x06, 0x7d, 0x8d, 0x8f, 0x9e, 0x24, 0xec, 0xc7




Not sure what to do next....Thanks in advance for any help. ##