totp.c: simple, standalone TOTP

totp.c is a small, simple, standalone command line TOTP (RFC6238) without any external dependencies.

totp.c was written by David M. Syzdek.

The standalone hmac_sha1 implementation is by Bob Liu.

Building

# use the default rlimit process restrictions
make

# use the seccomp process restrictions
RESTRICT_PROCESS=seccomp make clean all

# disable the process restrictions
RESTRICT_PROCESS=null make clean all

#### using musl
## sudo apt install musl-dev musl-tools
RESTRICT_PROCESS=rlimit ./musl-make

## linux seccomp process restrictions: requires kernel headers
export MUSL_INCLUDE=/tmp
git clone https://github.com/sabotage-linux/kernel-headers.git $MUSL_INCLUDE/kernel-headers
./musl-make clean all

Usage

Usage: totp <b32_key> [ <interval> [ <offset> ] ]

totp YW2N4W7UBAIAEVCT

# 30 second intervals (default)
totp YW2N4W7UBAIAEVCT 30

# previous window
totp YW2N4W7UBAIAEVCT 30 -30

# next window
totp YW2N4W7UBAIAEVCT 30 30

# read key from stdin
echo YW2N4W7UBAIAEVCT | totp - 30

Why?

I needed a simple TOTP application that could be statically linked for use on an old powerpc linux device.