otp_auth

A set of TOTP and HOTP examples that utilize MT64

Compile the code

./compile.sh

Create the shared secret key file

This is your secret key. Keep it private.
This file will seed the MT PRNG.

./gen_secret.sh: <openssl|dd> <file>

./gen_secret.sh openssl 256.bin
<or>
./gen_secret.sh dd 256.bin

Static Key

Run the MT64 to generate a static key based only on the secret keyfile.
This is just used to demonstrate the usage of the MT64 algorithm.
This will not produce a "One-Time" value. The input will not be manipulated.
It will reproduce consistent output from the same input.
Set the spin value to any unsigned integer.

./static_key.exe: <SECRET FILE> <SPIN VALUE>

./static_key.exe 256.bin 1000000

Time-based OTP

The totp example will use the current time to manipulate the MT seed.

./totp.exe: <SECRET FILE> <SPIN VALUE>

./totp.exe 256.bin 1000000
TOTP: B4DE50FC4428E12A6211A64C59244FE168B7FF0BD800056DD353EF9CEA6E59A9 (valid for   34s)
<wait 60s>
./totp.exe 256.bin 1000000
TOTP: EE7A8C7603AE9E38DD9FA38E8BBE75F8735B2417159C55D338621C9A66C95ED7 (valid for   35s)

Counter-based OTP

The hotp example will use an external counter value to manipulate the MT seed.
Currently any resyncing and validation window handling is not part of this code.

./hotp.exe: <SECRET FILE> <SPIN VALUE>

HOTP_COUNTER=47 ./hotp.exe 256.bin 1000000
HOTP: 9ECFCD099E264C6CAFD09FFBB6B6D09C1A0D079AC32B8FF2A719294C30AC1630

HOTP_COUNTER=48 ./hotp.exe 256.bin 1000000
HOTP: 43E55DFDFF921E45EC494A18CECB7201B550E0818882D0200AFEE950C6D58975

Design Decisions

This code was not designed to be compliant with any RFC or specification. It was strictly designed to generate OTP codes for use in an external authentication system. Currently the output is 32 bytes of binary data (represented as 64 hex digits). This can be adjusted higher or lower by changing OUTPUT_ULONGS in main.c

More Info

• Mersenne Twister
• TOTP
• HOTP