In cryptography, the one-time pad (OTP) is a type of encryption that is impossible to crack if used correctly.

The OTP

The OTP or one time pad is commonly held up as the one example of an unbreakable cipher. Yet NSA has clearly described breaking the VENONA cipher, which used an OTP, during the Cold War. It is argued that VENONA was "poorly used," but if a user has no way to guarantee a cipher being "well used," there is no reason for a user to consider an OTP strong at all.

It does seem convenient for NSA that a potentially breakable cipher continues to be described by crypto authorities as absolutely "unbreakable."

At least two professional, fielded systems which include OTP ciphering have been broken in practice by the NSA. The most famous is VENONA, which has its own pages at http://www.nsa.gov/docs/venona/. VENONA traffic occurred between the Russian KGB or GRU and their agents in the United States from 1939 to 1946. A different OTP system break apparently was described in: "The American Solution of a German One-Time-Pad Cryptographic System," Cryptologia XXIV(4): 324-332. These were real, life-and-death OTP systems, and one consequence of the security failure caused by VENONA was the death by execution of Julius and Ethel Rosenberg. Stronger testimony can scarcely exist about the potential weakness of OTP systems. And these two systems are just the ones NSA has told us about.