I am trying to use the AES engine of the LPC18S37 in ECB-mode to encrypt a 16-bytes plaintext. I obtain a ciphertext, which I then take through the decryption process to verify that I get the same original plaintext, which I do.
However, as a safety measure, I also desired to verify using an external resource, and therefore encrypted the same plaintext using a Python API (Crypto.Cipher.AES) in ECB-mode) but I didn't get the same ciphertext as from the MCU. The problem is that when I decrypt the Python version of the ciphertext, result is the same original plaintext.
I verified the lib's algorithm implementation, comparing it to the FIPS-197 standard : It is properly implemented.
I therefore assume that the problem most likely comes from my implementation of the code in the MCU.
I took of course care of verifying that the keys and plaintexts were strictly the same in both scenarios.
If anybody has advices or knows how to solve the problem, I would gladly welcome any ideas.
Thank you in advance.
Here are the relevant parts of the implementation of the MCU program :
//Set buffers :
uint8_t RX_plaintext; / /Contains a 16-bytes plaintext
uint8_t TX_plaintext; // WILL contain a 16-bytes plaintext after decryption
uint8_t RX_key; // Contains a 16-bytes key
uint8_t TX_ciphertext; // WILL contain the 16-bytes ciphertext after encryption
Chip_AES_LoadKeySW((uint8_t *) RX_key); // I like using verbose casts but this works the same way even without them
Chip_AES_Operate((uint8_t *)TX_ciphertext, (uint8_t *)RX_plaintext, 1);
Chip_AES_Operate((uint8_t *)TX_plaintext, (uint8_t *)TX_ciphertext, 1);