I used Poly1305, but exactly in the way Daniel J. Bernsetein used it in his NaCl library. I also used his ECC signature scheme, also in exactly the same way. :)

I used Poly1305, but exactly in the way Daniel J. Bernsetein used it in his NaCl library. I also used his ECC signature scheme, also in exactly the same way. :) As far as I can tell the gotcha with Poly1305 is that you absolutely cannot reuse the same key ever. His construction involves using your keyed cipher to create 32 random bytes by encrypting 32 zero bytes before encrypting the actual message. These random bytes are then used as the one-time-use Poly1305 key. In NaCl he does this with either Salsa20 or AES-CTR, both of which are stream ciphers. (CTR converts a block cipher into a stream cipher.)