A bash function to generate TOTP codes

totp.sh

#!/usr/bin/env bash

set -euo pipefail

# Generates a TOTP code and copies it to your clipboard. Hardcode your own key if you'd like.
#
# Usage: totp [key-base32]
#
# Dependencies: openssl, coreutils (base32)

hex2bin() {
  for ((i = 0; i < ${#1}; i += 2)); do
    printf '%b' "\\x${1:i:2}"
  done
}

bin2hex() {
  od -An -tx1 | tr -d ' \n'
}

# generate_totp key [time_sec [digits]]
generate_totp() {
  key=$1
  key_hex=$(tr '[:lower:]' '[:upper:]' <<<"$key" | base32 -d | bin2hex)
  time_sec=${2:-$(date +%s)}
  digits=${3:-6}
  time_step=$((time_sec / 30))
  time_step_hex=$(printf "%016x" $time_step)
  hash_hex=$(hex2bin "$time_step_hex" | openssl sha1 -mac HMAC -macopt "hexkey:$key_hex" -binary | bin2hex)
  offset=$((16#${hash_hex:39}))
  offset_str="${hash_hex:$((offset * 2)):8}"
  byte0=$(((16#${offset_str:0:2} & 127) << 24))
  byte1=$((16#${offset_str:2:2} << 16))
  byte2=$((16#${offset_str:4:2} << 8))
  byte3=$((16#${offset_str:6:2}))
  bin_code=$((byte0 + byte1 + byte2 + byte3))
  printf "%0${digits}d" $((bin_code % (10 ** digits)))
}

copy() {
  if command -v pbcopy &> /dev/null; then
    pbcopy
  elif command -v xclip &> /dev/null; then
    xclip -selection clipboard
  elif command -v wl-copy &> /dev/null; then
    wl-copy
  fi
}

generate_totp "${1:-AC6ZWNRLFOG5JUQHC5YW6BXX2K675AZL}" | tee >(copy)

# Print a newline after the code, but we don't want it in the clipboard
printf "\n"