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Poly1305-AES is a cryptographic message authentication code (MAC) written by Daniel J. Bernstein. As such, it may be used to simultaneously verify both the data integrity and the authenticity of a message.

Contents 1 Description 2 Security 3 Speed 4 External links 5 References

Poly1305-AES computes a 16-byte authenticator of a variable-length message, using a 16-byte AES key, a 16-byte additional key, and a 16-byte nonce. The name is derived from the use of the prime number 2¹³⁰ - 5 and the Advanced Encryption Standard. Since it uses a 130 bit prime, and works on 16 byte (128 bit) portions of message data, the algorithm works best when used with an bignum package, such as the GNU Multi-Precision Library used in most of the sample code provided by the author.

The security of Poly1305-AES is very close to the underlying AES block cipher algorithm. As a result, the only way for an attacker to break Poly1305-AES is to break AES.

For instance, assuming that messages are packets up to 1024 bytes; that the attacker sees 2⁶⁴ messages authenticated under a Poly1305-AES key; that the attacker attempts a whopping 2⁷⁵ forgeries; and that the attacker cannot break AES with probability above δ; then, with probability at least 0.999999 − δ, all the 2⁷⁵ are rejected^[1].

Poly1305-AES offers also cipher replaceability. If anything does go wrong with AES, it can be substituted with identical security guarantee.

Poly1305-AES can be computed at high speed in various CPUs: for an n-byte message, no more than 3.1n+780 Athlon cyles are needed^[1], for example. The author has released optimized implementations for Athlon, Pentium Pro/II/III/M, PowerPC and UltraSPARC, in addition to non-optimized reference implementations in C and C++.

• Poly1305-AES
• Poly1305-AES paper, complete specification, discussion of security bounds and details on implementation.
• Public domain Poly1305 library

1. ^ ^{a b} The Poly1305-AES message-authentication code, Daniel J. Bernstein

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