I have been reading about encrypting and authentication. Traveled the path from home made authentication to encrypt-then-mac approach and finally settled on GCM mode.
I am curious what resided inside aes_256_gcm. What is obvious from the name: AES algo and 256bit key length. IV len I could figure out from EVP_CIPHER_iv_length() call = 12 (I can change that with ctrl) Block size I could figure out from EVP_CIPHER_block_size() = 1
But what about "operation mode", CBC, OFB, CFB, other ? In what mode does the GCM runs ? Can I select the mode ?