Package poly1305 implements Poly1305 one-time message authentication code as specified in http://cr.yp.to/mac/poly1305-20050329.pdf.
Poly1305 is a fast, one-time authentication function. It is infeasible for an attacker to generate an authenticator for a message without the key. However, a key must only be used for a single message. Authenticating two different messages with the same key allows an attacker to forge authenticators for other messages with the same key.
Poly1305 was originally coupled with AES in order to make Poly1305-AES. AES was used with a fixed key in order to generate one-time keys from an nonce. However, in this package AES isn't used and the one-time key is specified directly.
const TagSize = 16
TagSize is the size, in bytes, of a poly1305 authenticator.
Sum generates an authenticator for m using a one-time key and puts the 16-byte result into out. Authenticating two different messages with the same key allows an attacker to forge messages at will.
Verify returns true if mac is a valid authenticator for m with the given key.