#!/bin/bash
# Desc: Generate passphrase with specified number of bits of entropy
# Usage: bknpass [integer]
# Example: bknpass 256
# Result: 9tnzcl0m4dsm22a95525zj93jj
# Version: 0.2.1
# Depends: bash 5.1.8, GNU coreutils 8.32, bc 1.07.1, awk 5.1.0
# License:
# `bknpass`, an alphanumeric password generator
# Copyright (C) 2022 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
# .
yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
try() { "$@" || die "cannot $*"; } # runs args as command, reports args if command fails
showUsage() {
# Desc: Display script usage information
# Usage: showUsage
# Version 0.0.1
# Input: none
# Output: stdout
# Depends: GNU-coreutils 8.30 (cat)
cat <<'EOF'
USAGE:
bknpass [int entropy_bit_count]
EXAMPLE:
bknpass 128
EOF
}; # Display information on how to use this script.
main() {
# Desc: main program
# Usage: main "$@"
# Input: $1: integer bits of entropy
# Output: stdout: string passphrase
# Depends: bash 5.1.8, GNU coreutils 8.32, bc 1.07.1, awk 5.1.0
# Ref/Attrib: [1] "Check existence of input argument in a Bash shell script". https://stackoverflow.com/a/6482403
# [2] "How do I test if a variable is a number in Bash?". https://stackoverflow.com/a/806923
# [3] "Round a Number in a Bash Script". https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
# [4] "Logarithms in GNU bc". https://web.archive.org/web/20210211050732/http://phodd.net/gnu-bc/bcfaq.html#bclog
# [5] "BIP 173". Note: bech32 charset. https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
# [6] "Bash Function to generate random password". https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
charset="qpzry9x8gf2tvdw0s3jn54khce6mua7l"; # bech32. See [5].
charset="$(tr -s "$charset" < <(echo -n "$charset"))"; # remove repeat chars
alphabet_size="$(echo -n "$charset" | wc -c)"; # number of unique chars
log_base=2; # entropy unit base (i.e. 2 for "bits of entropy")
# Check inputs
if [[ $# -gt 1 ]]; then showUsage; die "ERROR:Too many arguments:$#"; fi;
# Check for bc
if ! command -v bc 1>/dev/null 2>&1; then die "ERROR:bc not available"; fi;
## Get entropy_bit_count
if [[ -z "$1" ]]; then
### prompt user
showUsage;
echo -n "Please specify the required strength of the password in bits of entropy (ex: 256):" 1>&2; # prompt via stderr
read -r entropy_bit_count
else
entropy_bit_count="$1";
fi; # See [1].
## Check entropy_bit_count
pattern="^[0-9]+$";
if ! [[ $entropy_bit_count =~ $pattern ]] ; then die "ERROR:Not an integer:$entropy_bit_count"; fi; # See [2]
## Calculate minimum count of chars needed for passphrase as float using 'bc'
### Solve ln(a^n)/ln(2)=b for n where:
### a=$alphabet_size
### n=$char_count_float
### b=$entropy_bit_count
char_count_float="$(echo "$entropy_bit_count*l($log_base)/l($alphabet_size)" | bc -l)"; # See [4]
## Round $char_count_float to next highest integer
char_count="$(echo "$char_count_float" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')"; # See [3]
## Generate and output passphrase
echo "$(LC_ALL=C tr -cd "$charset" < /dev/urandom | head -c "$char_count")"; # See [6]
}; # main program
( main "$@" ); # run 'main()' in subshell for 'die()' portability of script as sourced bash function.
#==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, bc, echo, awk, tr, head
#
# - GNU bash, version 5.1.8(1)-release (x86_64-pc-linux-gnu)
# Copyright (C) 2020 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.
#
# - bc 1.07.1
# Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
#
# - echo (GNU coreutils) 8.32
# Copyright (C) 2020 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.
#
# - GNU Awk 5.1.0, API: 3.0 (GNU MPFR 4.1.0, GNU MP 6.2.1)
# Copyright (C) 1989, 1991-2020 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) 8.32
# Copyright (C) 2020 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) 8.32
# Copyright (C) 2020 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.