Common
HMAC-based one-time password
Password authentication algorithm
HMAC-based one-time password
HMAC-based one-time password (HOTP) is a cryptographic algorithm based on a one-time password (OTP) and hash-based message authentication code (HMAC). At setup time, a client and server share a secret and other initialization settings. In future exchanges, when a client attempts to access a server, a challenge is sent from the server to the client and the client then uses the previously exchanged secret and computes a value (a one time password) to be used as the server's challenge response. HOTP is the basis for the commonly used time-based one-time password (TOTP) algorithm which extends upon it. It often forms part of multi-factor authentication protocols such as the Open Authentication initiative (OATH).. HOTP was published as an informational IETF RFC 4226 in December 2005, documenting the algorithm along with a Java implementation. Since then, the algorithm has been adopted by many companies worldwide (see below).
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