-----BEGIN PGP SIGNED MESSAGE----- In article <199601221851.NAA16938@amsterdam.lcs.mit.edu>, David Mazieres <dm@amsterdam.lcs.mit.edu> wrote:
The problem with RC4 is that it works in OFB only. If I need data integrity in the face of known plaintext, I will need to compute a MAC in paralell with the encryption which could significantly slow things down.
If you want authentication, you must use a crypto-strength MAC. Encryption (be it RC4, DES, etc.) is not enough.
With a block cypher in CFB, I can just re-encrypt the last block of data.
False. CFB has limited error propagation, so if I modify any block before the next-to-last, it will not show up with your method. This seems to be a really common error. If you want message integrity guarantees, you must use a MAC. Always. - --- [This message has been signed by an auto-signing service. A valid signature means only that it has been received at the address corresponding to the signature and forwarded.] -----BEGIN PGP SIGNATURE----- Version: 2.6.2 Comment: Gratis auto-signing service iQBFAwUBMQV+LioZzwIn1bdtAQF7pgGAm6GnmZqPSElx8mVyonD9BqScefdZLhul fv/qU/bsEDM2YyKuBpoFWyKMwIH0jyzx =Bp2Q -----END PGP SIGNATURE-----