|This article relies on references to primary sources. (October 2013)|
Poly1305-AES computes a 128-bit (16 bytes) authenticator of a variable-length message, using a 128-bit AES key, a 106-bit additional key, and a 128-bit nonce. The name is derived from the use of the prime number 2130−5 and the Advanced Encryption Standard.
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.
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 cycles are needed, 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++.
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