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This is an early experiment in human-computable TOTP. Not production crypto, but a serious attempt to reach reasonable security for plausible 2FA. Protocol revisions, criticism, and contributions are welcome.

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I don't really get what tone you're doing for. Is this "a serious attempt", or is this "something that does not guarantee any cryptographic security"?

Nonetheless I do not see what issues 2FA has that this solves. Having the electronic device is the security. Without it there is no security.

The security advantage I see in mtotp is that you never reveal the password to the system you are authenticating with, but that there is also no electronic device that can be compromised

The algorithm for the checksum (the sixth digit) is subject to one of the most common human errors, swapping adjacent digits. The UPC checksum algorithm handles this without significantly more complexity. They have you multiply all of the numbers in odd positions by 3 and then add up all numbers. The last digit is chosen to make the sum a multiple of 10.

To use your example: 51076, you'd do `5*3 + 1 + 0*3 + 7 + 6*3 = 15 + 1 + 0 + 7 + 18 = 41`. The sixth digit would be 9 ((10 - (41 mod 10)) mod 10). If you were to transpose any two adjacent numbers the checksum would be off. 3 is chosen because it's the smallest number that is co-prime with 10.

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