Method __builtin.Nettle.Hash()->hotp()

Method hotp

int hotp(string(8bit) secret, int factor, int(1..)|void length)

Description

HMAC-Based One-Time Password as defined by RFC 4226.

Can be used to implement the RFC 6238 Time-Based One-Time Password Algorithm by giving the factor (time()-T0)/X. Specifically for Google Authenticator this is Crypto.SHA1.hotp(secret,time()/30), using an 80 bit secret.

Parameter secret

A shared secret between both parties. Typically the same size as the hash output.

Parameter factor

A moving factor. Defined in RFC 4226 to be a counter synchronized between both parties.

Parameter length

The maximum number of digits of the one-time password. Defaults to 6. Note that the result is usually 0-padded to this length for user display purposes.