OATH Challenge Response Algorithm.
This is generalization of the HOTP algorithm. Flexible input data can be used instead of the counter. Such input data is the challenge and can additionally be a PIN, a timestamp, a counter etc.The kind of the required input data is defined in a so called “OCRA suite”.
This algorithm can be used to “sign” information if the hash value of the information is used as the challenge data.
It is defined in RFC 6287.