Comment by lifthrasiir

5 days ago

It is even shorter without boilerplates:

    def hotp(key, counter, digits=6, digest='sha1'):
        key = base64.b32decode(key.upper() + '=' * ((8 - len(key)) % 8))
        counter = struct.pack('>Q', counter)
        mac = hmac.new(key, counter, digest).digest()
        offset = mac[-1] & 0x0f
        binary = struct.unpack('>L', mac[offset:offset+4])[0] & 0x7fffffff
        return str(binary)[-digits:].zfill(digits)
    
    def totp(key, time_step=30, digits=6, digest='sha1'):
        return hotp(key, int(time.time() / time_step), digits, digest)

2 comments

lifthrasiir

Reply
notpushkin  5 days ago

Ever so slightly easier to read (IMO) if you inline arguments:

    def hotp(key: bytes, counter: int, digits: int = 6, digest: Literal["sha1", "sha256", "sha512"] = "sha1"):
        mac = hmac.digest(
            key=base64.b32decode(key.upper() + "=" * ((8 - len(key)) % 8)),
            msg=struct.pack(">Q", counter),
            digest=digest,
        )
        offset = mac[-1] & 0x0F
        binary: int = struct.unpack(">L", mac[offset : offset + 4])[0] & 0x7FFFFFFF
        return str(binary)[-digits:].zfill(digits)

And Pyright doesn’t yell at this version because no type-changing variables here: https://basedpyright.com/?typeCheckingMode=all&code=JYWwDg9g...

---

This is actually really helpful. I’m using Pass [1], which requires oathtool for OTP support [2]. I’m currently on a Mac without admin rights (so no Homebrew for me), and compiling oathtool is a PITA. I’ve wanted to put together a pure Python replacement for a while now, but with this it can be a single-file script: https://gist.github.com/notpushkin/7ac32ddf35a0c73bc6f181a1b...

[1]: https://www.passwordstore.org/

[2]: https://github.com/tadfisher/pass-otp#requirements