README.md

OTP: HMAC-Based and Time-Based One-Time Passwords (HOTP & TOTP)

Please refer to the package description for an overview of OTP.

Usage examples

Generating one-time passwords

If you need to generate HOTP password described in RFC4226, then use

>>> hotp SHA1 "1234" 100 6
317569

>>> hotp SHA512 "1234" 100 6
134131

Or

>>> totp SHA1 "1234" (read "2010-10-10 00:01:00 UTC") 30 8
43388892

to generate TOTP password described in RFC6238.

Checking one-time passwords

hotpCheck :: HashAlgorithm      -- ^ Hashing algorithm
          -> Secret             -- ^ Shared secret
          -> (Word8, Word8)     -- ^ how much counters to take lower and higher than ideal
          -> Word64             -- ^ ideal (expected) counter value
          -> Word8              -- ^ Number of digits in password
          -> Word32             -- ^ Password entered by user
          -> Bool               -- ^ True if password acceptable

>>> hotpCheck SHA1 "1234" (0,0) 10 6 50897
True

>>> hotpCheck SHA1 "1234" (0,0) 9 6 50897
False

>>> hotpCheck SHA1 "1234" (0,1) 9 6 50897
True

Here almost the same aguments as for hotp function, but there is also (0, 0) tuple. This tuple describes range of counters to check in case of desynchronisation of counters between client and server. I.e. if you specify (1, 1) and ideal counter will be 10 then function will check passwords for [9, 10, 11] list of counters.

Here is the same for TOTP:

>>> totpCheck SHA1 "1234" (0, 0) (read "2010-10-10 00:00:00 UTC") 30 6 778374
True

>>> totpCheck SHA1 "1234" (0, 0) (read "2010-10-10 00:00:30 UTC") 30 6 778374
False

>>> totpCheck SHA1 "1234" (1, 0) (read "2010-10-10 00:00:30 UTC") 30 6 778374
True