No abstract

Counter with CBC-MAC (CCM) is a generic authenticated encryption block cipher mode. CCM is defined for use with 128-bit block ciphers, such as the Advanced Encryption Standard (AES).

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Helix is a high-speed stream cipher with a built-in MAC functionality. On a Pentium II CPU it is about twice as fast as Rijndael or Twofish, and comparable in speed to RC4. The overhead per encrypted/authenticated message is low, making it suitable for small messages. It is efficient in both hardware and software, and with some pre-computation can effectively switch keys on a per-message basis without additional overhead.

We present a new construction for off-line electronic coins that is both far more efficient and much simpler than previous systems. Instead of using many terms, each for a single bit of the challenge, our system uses a single term for a large number of possible challenges. The withdrawal protocol does not use a cutand-choose methodology as with earlier systems, but uses a direct construction.