Secret length too short according to standard

[hannob]

The secret created by the createSecret() function is too short according to the standard.

The TOTP standard references the HOTP RFC for the algorithm, which is RFC 4226. It says:

   The algorithm MUST use a strong shared secret.  The length of
   the shared secret MUST be at least 128 bits.  This document
   RECOMMENDs a shared secret length of 160 bits.

The secret created in your code is by default 16 bytes base32 encoded. That corresponds to an 80 bit secret. (There is probably a common misunderstanding that people believe 16 bytes corresponds to 16*8 bits, but that ignores the base32 encoding, which reduces the character space by 3 bits.)

In theory this could be considered a security vulnerability. However it's a very theoretical one, as 80 bits is still a security level that is probably outside the possibilities of any real attacker. However it gets somewhat dangerously close to what could be broken by a powerful attacker, so better stick to the recommendation from the standard.

Here's also a blogpost discussing too short TOTP secrets (however I found the blogpost a bit confusing and it took me a while to realize that with a 16 byte secret we're still far away from any practical attack):
https://www.unix-ninja.com/p/attacking_google_authenticator