AES CFB and XTS

Two modes of AES have been added to the embedded TLS library wolfSSL; AES-CFB and AES-XTS.

AES CFB (Cipher FeedBack) mode is a stream cipher mode of AES. For the first 16 bytes it encrypts an IV using AES and xor’s the result with the plain text for encryption or the cipher text for decryption. For getting the rest of the output the previous 16 bytes is encrypted with AES then xor’d with either the plain text or the cipher text.

AES XTS (XEX encryption with Tweak and ciphertext Stealing) mode is also a stream cipher mode. It is used for disk encryption and has an xor encrypt xor model with a Galois field multiplication for counter. When the input is not a multiple of AES block size (16 bytes), stealing is done to fill out the input size to a complete AES block size. This is done by copying over from the last full AES block size produced.

Both of these modes can be used in IoT applications and take advantage of existing AES hardware acceleration supported by wolfSSL.

For more information about AES modes in wolfSSL contact info@wolfssl.com.