The Digital Signature Algorithm (DSA) is a United States Federal Government standard or FIPS for digital signatures. It was proposed by the National Institute of Standards and Technology (NIST) in August 1991 for use in their Digital Signature Standard (DSS), specified in FIPS 186, adopted in 1993. A minor revision was issued in 1996 as FIPS 186-1, and the standard was expanded further in 2000 as FIPS 186-2.
DSA is covered by U.S. Patent 5,231,668 , filed July 26, 1991, and attributed to David W. Kravitz, a former NSA employee. This patent was given to "The United States of America as represented by the Secretary of Commerce, Washington, D.C." and the NIST has made this patent available world-wide royalty-free. Dr. Claus P. Schnorr claims that his U.S. Patent 4,995,082 covers DSA; this claim is disputed (see minutes of the Sept. 94 meeting of the Computer System Security and Privacy Advisory Board).
Reference:
http://en.wikipedia.org/wiki/Digital_Signature_Algorithm
