#!/bin/bash
# Author: Steven Baltakatei Sandoval (baltakatei.com)
#
# License: This bash script, `bknpass`, is licensed under GPLv3 or
# later by Steven Baltakatei Sandoval:
#
# `bknpass`, an alphanumeric password generator
# Copyright (C) 2021 Steven Baltakatei Sandoval (baltakatei.com)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# A copy of the GNU General Public License may be found at
# .
#
# Description: This bash script generates alphanumeric passphrases
# with a char-count determined by a user-provided number of bits of
# entropy. The passphrase is then outputted to stdout with a trailing
# newline. It works as follows:
#
# - Prompt user for an integer. This integer is the number of bits
# of entropy that the generated password should have.
#
# - Check if user-provided string is an integer using `bash` regular
# expression test.
#
# - Calculate the minimum number of bech32 base32 characters
# required to encode the specified number of bits of entropy.
#
# - This step uses `bc` to calculate a logarithm float string
# and `awk` to convert the float into an integer, rounding up.
#
# - Use `tr`, `/dev/urandom`, and `head` to generate a random
# alphanumeric string with the length calculated in the previous
# step.
#
# - Use `echo` to display the passphrase in stdout with a trailing
# newline.
#
# Usage: bknpass [int]
#
# Example: bknpass 256
#
# Dependencies: bash, echo, bc, awk, tr, head. See end of file
#
# Tested on:
#
# - GNU/Linux Debian 10
#==Initialization==
let ALPHABET_SIZE="32" # number of unique chars in bech32 base32 charset
LOG_BASE=2 # Set logarithm base to 2
# Define `echoerr` function which outputs text to stderr
# Note: function copied from https://stackoverflow.com/a/2990533
function echoerr {
echo "$@" 1>&2;
}
# Define `rpass` function which generates a base32 passphrase of length $1 (ex: `rpass 20` generates a 20-char string)
# Note: function adapted from https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
# Note: base32 charset uses bech32 charset
function rpass {
cat /dev/urandom | LC_ALL=C tr -cd "qpzry9x8gf2tvdw0s3jn54khce6mua7l" | head -c ${1:-22}
}
#==Main Program==
# Define $ENTROPY_BIT_COUNT1 as argument $1 or prompt user if $1 is not defined.
# Note: argument test adapted from https://stackoverflow.com/a/6482403
if [ -z "$1" ]
then
echo "Entropy bit count argument (\$1) not supplied."
# Get from user the number of bits of entropy.
echoerr -n "Please specify the required strength of the password in bits of entropy (ex: 256):" # prompt via stderr
read ENTROPY_BIT_COUNT1
else
ENTROPY_BIT_COUNT1="$1"
fi
# Check if $ENTROPY_BIT_COUNT1 is an non-negative integer
# Note: Regular expression test is adapted from https://stackoverflow.com/a/806923
RETEST1='^[0-9]+$'
if ! [[ $ENTROPY_BIT_COUNT1 =~ $RETEST1 ]] ; then
echo "error: Not an integer." >&2; exit 1
fi
# Calculate minimum count of chars needed to encode $ENTROPY_BIT_COUNT1 with alphabet size of $ALPHABET_SIZE as float
# Solve ln(a^n)/ln(2)=b for n using `bc` where
# a=$ALPHABET_SIZE
# n=$CHAR_COUNT1_FLOAT
# b=$ENTROPY_BIT_COUNT1
# Note: `bc` logarithm usage adapted from http://phodd.net/gnu-bc/bcfaq.html#bashlog
CHAR_COUNT1_FLOAT=$(echo "$ENTROPY_BIT_COUNT1*l($LOG_BASE)/l($ALPHABET_SIZE)" | bc -l)
# Note: Float will be of form "21.49744370650136860806".
# Note: This particular example float should be rounded to "22" later.
# Round $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions.
# Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')
# Generate passphrase
PASS1=$(rpass "$CHAR_COUNT1")
echo -e "$PASS1"
#==References==
#
# - How to echo a string as stderr instead of stdout.
# https://stackoverflow.com/a/2990533
# Author: James Roth
# Date: 2010-06-07T14:52Z
# Date Accessed: 2020-01-20
#
# - How to check if script argument exists or not.
# https://stackoverflow.com/a/6482403
# Author: phoxix
# Date: 2011-06-26T05:55Z
# Date Accessed: 2020-01-20
#
# - How to check that a string is an integer using regular expression test.
# https://stackoverflow.com/a/806923
# Author: Charles Duffy
# Date: 2009-04-30T13:32Z
# Date Accessed: 2020-01-20
#
# - How to use `bc` to calculate logarithms in Bash
# http://phodd.net/gnu-bc/bcfaq.html#bashlog
# Author: unknown
# Date Accessed: 2020-01-20
#
# - How to use `awk` to convert and round up a float to an integer.
# https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
# Author: Md. Minhazul Haque
# Date: 2015-01-09
# Date Accessed: 2020-01-20
#
# - How to use `/dev/urandom`, `tr`, and `head` to generate a random password in Bash.
# https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
# Author: SASIKALA, Ramesh Natarajan
# Date: 2010-04-21
# Date Accessed: 2020-01-20
#
# - Bech32 base32 charset
# https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
# Author: Pieter Wuille
# Date: 2017-03-20
# License: BSD-2-Clause
# Date: Accessed: 2021-01-23
#
# - Dependencies: bash, echo, bc, awk, tr, head.
#
# - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)
# Copyright (C) 2019 Free Software Foundation, Inc.
# License GPLv3+: GNU GPL version 3 or later
# This is free software; you are free to change and redistribute it.
# There is NO WARRANTY, to the extent permitted by law.
#
# - echo (GNU coreutils) 8.30
# Copyright (C) 2018 Free Software Foundation, Inc.
# License GPLv3+: GNU GPL version 3 or later .
# This is free software: you are free to change and redistribute it.
# There is NO WARRANTY, to the extent permitted by law.
#
# Written by Brian Fox and Chet Ramey.
#
# - bc 1.07.1
# Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
#
# - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
# Copyright (C) 1989, 1991-2018 Free Software Foundation.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see http://www.gnu.org/licenses/.
#
# - tr (GNU coreutils) 8.30
# Copyright (C) 2018 Free Software Foundation, Inc.
# License GPLv3+: GNU GPL version 3 or later .
# This is free software: you are free to change and redistribute it.
# There is NO WARRANTY, to the extent permitted by law.
#
# Written by Jim Meyering.
#
# - head (GNU coreutils) 8.30
# Copyright (C) 2018 Free Software Foundation, Inc.
# License GPLv3+: GNU GPL version 3 or later .
# This is free software: you are free to change and redistribute it.
# There is NO WARRANTY, to the extent permitted by law.
#
# Written by David MacKenzie and Jim Meyering.