In 1984, Shafi Goldwasser, Silvio Micali, and Ronald Rivest became the first to strictly define the security requirements of digital signature schemes. They described a hierarchy of attack models for signature schemes, they also present the GMR signature scheme. GMR scheme was proven to be secure against adaptive chosen-message attacks — even when an attacker receives signatures for messages of his choice, this does not allow him to copy a signature for a single additional message.