The Digital Signature Standard is defined in FIPS PUB 186-4. It defines the Digital Signature Algorithm, contains a definition of RSA signatures based on the definitions contained within PKCS #1 version 2.1 and in American National Standard X9.31 with some additional requirements, and contains a definition of the Elliptic Curve Digital Signature Algorithm based on the definition provided by American National Standard X9.62 with some additional requirements and some recommended elliptic curves. It also approves the use of all three algorithms.