The TOI payload, prior to encryption, is 165 bits in length. Conforming to the AES Encryption scheme with a 128-bit cipher key, the encrypted part of the payload then effectively becomes 256 bits in length to create blocks of 128 bits.
Links[1] https://www.e-navigation.nl/sites/default/files/asm_files/epic-15-05-29-uscg-foia-20151030-production-2.pdf