Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

According to the specification of RFC 4764, contents in EAP's third message and fourth message are required to be encrypted by AES-128 in EAX mode (also called protected channel).

In RFC 4764, the length of ciphertext is as the same as the length of plaintext. However, the test vectors in The EAX Mode of Operation show that the ciphertext must be longer than the plaintext.

Therefore, what happens in RFC 4764?

share|improve this question

In RFC 4764, the ciphertext does not include the authentication tag created by EAX (which is treated separately); you can see this in figure 1, where they show the ciphertext (of length L) and the tag separately.

In contrast, the test vectors do include the authentication tag, and that additional length make the ciphertexts look longer.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.