Steam Guard Token Generator

sguard.sh

#!/bin/sh

set -e

# To get the Secret value follow this:
# https://github.com/steamguard-totp/steamguard-shared-secret
# Don't forget to unescape '/' if there is

file="$(dirname "$(readlink -f "$0")")/steam.secret"

time=$(date -u +%s)

chars='23456789BCDFGHJKMNPQRTVWXY'
len=${#chars}

sha=$(
printf '00000000%08x' "$(((time + 3600 * 0) / 30))" |
        xxd -r -p |
        openssl sha1 -mac HMAC -macopt "hexkey:$(
                base64 -d < "$file" | xxd -p
        )" |
        cut -d\  -f2
)

start=$(printf '%d' "0x$(printf '%s' "$sha" | tail -c1)")

code=$(($(
        printf '%d' "0x$(
                printf '%s' "$sha" | tail "-c+$((start * 2 + 1))" | head -c8
        )"
) & 0x7FFFFFFF))

for n in $(seq 1 5); do
        printf '%s' "$chars" | tail -c+$((code % len + 1)) | head -c1
        code=$((code / len))
done

printf '\nRemaining: %ss\n' "$((30 - time % 30))"