In the second chapter of Bruce Schneier's book Applied Cryptography, 2nd Edition, 1996, we find this:
- Alice encrypts her message to Bob with KA and sends it to Trent.
- Trent decrypts the message with KA.
- Trent takes the decrypted message and a statement that he has received this message from Alice, and encrypts the whole bundle with KB.
- Trent sends the encrypted bundle to Bob.
- Bob decrypts the bundle with KB. He can now read both the message and Trent’s certification that Alice sent it.
I don't understand the last step. The "certification" had not been mentioned in any of the previous steps.
Does "certification" mean "a statement that he has received this message from Alice"?