Function rusthotp::hotp [−] [src]

pub fn hotp(
    desired_code_length: usize, 
    key: &[u8], 
    counter: &[u8]
) -> HotpOutput

This implementation of HMAC-Based One Time Passwords proceeds in three stages, as per RFC 4226:

  1. Generate an HMAC-SHA-1 value given a shared secret key and a moving factor counter that should change on every use
  2. Extraction of a 4-byte value from the SHA-1 digest
  3. Deriving a final HOTP value between 0 and 10{desired_code_length}-1 from the 4-byte value extracted in the last step.

Note that it is the responsibility of the caller to:

  • Fulfill the precondition that counter is an 8-byte value
  • Increment the counter accordingly per invocation

Examples

To generate an HOTP value between 0 and 108 - 1, given the shared secret ASCII key "Hello world!" and current counter 0:

rusthotp::hotp(8, "Hello world!".as_bytes(), &[0; 8]);