"One project where my friend and officemate Steven T. Kent (now chief scientist and vice president at BBN, and a chief advisor to NSA) and I lost was our strong argument to put mandatory end-to-end encryption into TCP (and adaptations of the ideas to UDP-based protocols, such as RTP, hich I worked out but abandoned). Steve’s design was rejected, not because it was unsound, but because NSA did not want to see ANY encryption work going on in the public domain ARPA project, some say because they did not want to see the world be “too secure” by default. (Rivest and friends had just invented RSA, and the government was trying to declare it Top Secret, then later prohibited under ITAR munitions control export laws)."

http://www.reed.com/blog-dpr/?page_id=6