I have implemented the HMAC (RFC2104) in actionscript 3 using the as3 core library. I have submitted a patch to as3 core lib. I developed the HMAC library because I needed it to perform the CRAM-MD5 for my actionscript 3 mail api project AsMailer. The HMAC library has been tested for MD5 and SHA1. The library can support other hash methods but they have not been tested.