unitproc/bknpass

   1 #!/bin/bash
   2
   3 # Author: Steven Baltakatei Sandoval (baltakatei.com)
   4 #
   5 # License: This bash script, `bknpass`, is licensed under GPLv3 or
   6 # later by Steven Baltakatei Sandoval:
   7 #
   8 #    `bknpass`, an alphanumeric password generator
   9 #    Copyright (C) 2021  Steven Baltakatei Sandoval (baltakatei.com)
  10 #
  11 #    This program is free software: you can redistribute it and/or modify
  12 #    it under the terms of the GNU General Public License as published by
  13 #    the Free Software Foundation, either version 3 of the License, or
  14 #    any later version.
  15 #
  16 #    This program is distributed in the hope that it will be useful,
  17 #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 #    GNU General Public License for more details.
  20 #
  21 #    A copy of the GNU General Public License may be found at
  22 #    <https://www.gnu.org/licenses/>.
  23 #
  24 # Description: This bash script generates alphanumeric passphrases
  25 # with a char-count determined by a user-provided number of bits of
  26 # entropy. The passphrase is then outputted to stdout with a trailing
  27 # newline. It works as follows:
  28 #
  29 #   - Prompt user for an integer. This integer is the number of bits
  30 #     of entropy that the generated password should have.
  31 #
  32 #   - Check if user-provided string is an integer using `bash` regular
  33 #     expression test.
  34 #
  35 #   - Calculate the minimum number of bech32 base32 characters
  36 #     required to encode the specified number of bits of entropy.
  37 #
  38 #       - This step uses `bc` to calculate a logarithm float string
  39 #         and `awk` to convert the float into an integer, rounding up.
  40 #
  41 #   - Use `tr`, `/dev/urandom`, and `head` to generate a random
  42 #     alphanumeric string with the length calculated in the previous
  43 #     step.
  44 #
  45 #   - Use `echo` to display the passphrase in stdout with a trailing
  46 #     newline.
  47 #
  48 # Usage: bknpass [int]
  49 #
  50 # Example: bknpass 256
  51 #
  52 # Dependencies: bash, echo, bc, awk, tr, head. See end of file
  53 #
  54 # Tested on:
  55 #
  56 #   - GNU/Linux Debian 10
  57
  58
  59 #==Initialization==
  60
  61 let ALPHABET_SIZE="32" # number of unique chars in bech32 base32 charset, argument fed to `tr -c` in 'Generate passphrase' step)
  62 LOG_BASE=2 # Set logarithm base to 2
  63
  64 # Define `echoerr` function which outputs text to stderr
  65     # Note: function copied from https://stackoverflow.com/a/2990533
  66 function echoerr {
  67     echo "$@" 1>&2;
  68 }
  69
  70 # Define `rpass` function which generates a base32 passphrase of length $1 (ex: `rpass 22` generates a 22-char string)
  71 #   Note: function adapted from https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
  72 #   Note: base32 charset uses bech32 charset
  73 function rpass {
  74     cat /dev/urandom | LC_ALL=C tr -cd "qpzry9x8gf2tvdw0s3jn54khce6mua7l" | head -c ${1:-22}
  75 }
  76
  77
  78 #==Main Program==
  79
  80 # Define $ENTROPY_BIT_COUNT1 as argument $1 or prompt user if $1 is not defined.
  81     # note: argument test adapted from https://stackoverflow.com/a/6482403
  82 if [ -z "$1" ]
  83 then
  84     echo "Entropy bit count argument (\$1) not supplied."
  85     # Get from user the number of bits of entropy.
  86     echoerr -n "Please specify the required strength of the password in bits of entropy (ex: 256):" # prompt via stderr
  87     read ENTROPY_BIT_COUNT1
  88 else
  89     ENTROPY_BIT_COUNT1="$1"
  90 fi
  91
  92 # Check if $ENTROPY_BIT_COUNT1 is an non-negative integer
  93     # Note: Regular expression test is adapted from https://stackoverflow.com/a/806923
  94 RETEST1='^[0-9]+$'
  95 if ! [[ $ENTROPY_BIT_COUNT1 =~ $RETEST1 ]] ; then
  96    echo "error: Not an integer." >&2; exit 1
  97 fi
  98
  99 # Calculate minimum count of chars needed to encode $ENTROPY_BIT_COUNT1 with alphabet size of $ALPHABET_SIZE as float
 100     # Solve ln(a^n)/ln(2)=b for n using `bc` where
 101       # a=$ALPHABET_SIZE
 102       # n=$CHAR_COUNT1_FLOAT
 103       # b=$ENTROPY_BIT_COUNT1
 104     # Note: `bc` logarithm usage adapted from http://phodd.net/gnu-bc/bcfaq.html#bashlog
 105 CHAR_COUNT1_FLOAT=$(echo "$ENTROPY_BIT_COUNT1*l($LOG_BASE)/l($ALPHABET_SIZE)" | bc -l)
 106     # Note: Float will be of form "21.49744370650136860806". This particular float should be rounded to "22" later.
 107
 108 # Round $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions.
 109     # Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
 110 CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')
 111
 112 # Generate passphrase
 113 PASS1=$(rpass "$CHAR_COUNT1")
 114 echo -e "$PASS1"
 115
 116
 117 #==References==
 118 #
 119 # - How to echo a string as stderr instead of stdout.
 120 #   https://stackoverflow.com/a/2990533
 121 #   Author: James Roth
 122 #   Date: 2010-06-07T14:52Z
 123 #   Date Accessed: 2020-01-20
 124 #
 125 # - How to check if script argument exists or not.
 126 #   https://stackoverflow.com/a/6482403
 127 #   Author: phoxix
 128 #   Date: 2011-06-26T05:55Z
 129 #   Date Accessed: 2020-01-20
 130 #
 131 # - How to check that a string is an integer using regular expression test.
 132 #   https://stackoverflow.com/a/806923
 133 #   Author: Charles Duffy
 134 #   Date: 2009-04-30T13:32Z
 135 #   Date Accessed: 2020-01-20
 136 #
 137 # - How to use `bc` to calculate logarithms in Bash
 138 #   http://phodd.net/gnu-bc/bcfaq.html#bashlog
 139 #   Author: unknown
 140 #   Date Accessed: 2020-01-20
 141 #
 142 # - How to use `awk` to convert and round up a float to an integer.
 143 #   https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
 144 #   Author: Md. Minhazul Haque
 145 #   Date: 2015-01-09
 146 #   Date Accessed: 2020-01-20
 147 #
 148 # - How to use `/dev/urandom`, `tr`, and `head` to generate a random password in Bash.
 149 #   https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
 150 #   Author: SASIKALA, Ramesh Natarajan
 151 #   Date: 2010-04-21
 152 #   Date Accessed: 2020-01-20
 153 #
 154 # - Bech32 base32 charset
 155 #   https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
 156 #   Author: Pieter Wuille <pieter.wuille@gmail.com>
 157 #   Date: 2017-03-20
 158 #   License: BSD-2-Clause
 159 #   Date: Accessed: 2021-01-23
 160 #
 161 # - Dependencies: bash, echo, bc, awk, tr, head.
 162 #
 163 #     - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)
 164 #       Copyright (C) 2019 Free Software Foundation, Inc.
 165 #       License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 166 #       This is free software; you are free to change and redistribute it.
 167 #       There is NO WARRANTY, to the extent permitted by law.
 168 #
 169 #     - echo (GNU coreutils) 8.30
 170 #       Copyright (C) 2018 Free Software Foundation, Inc.
 171 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 172 #       This is free software: you are free to change and redistribute it.
 173 #       There is NO WARRANTY, to the extent permitted by law.
 174 #
 175 #       Written by Brian Fox and Chet Ramey.
 176 #
 177 #     - bc 1.07.1
 178 #       Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
 179 #
 180 #     - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
 181 #       Copyright (C) 1989, 1991-2018 Free Software Foundation.
 182 #
 183 #       This program is free software; you can redistribute it and/or modify
 184 #       it under the terms of the GNU General Public License as published by
 185 #       the Free Software Foundation; either version 3 of the License, or
 186 #       (at your option) any later version.
 187 #
 188 #       This program is distributed in the hope that it will be useful,
 189 #       but WITHOUT ANY WARRANTY; without even the implied warranty of
 190 #       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 191 #       GNU General Public License for more details.
 192 #
 193 #       You should have received a copy of the GNU General Public License
 194 #       along with this program. If not, see http://www.gnu.org/licenses/.
 195 #
 196 #     - tr (GNU coreutils) 8.30
 197 #       Copyright (C) 2018 Free Software Foundation, Inc.
 198 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 199 #       This is free software: you are free to change and redistribute it.
 200 #       There is NO WARRANTY, to the extent permitted by law.
 201 #
 202 #       Written by Jim Meyering.
 203 #
 204 #     - head (GNU coreutils) 8.30
 205 #       Copyright (C) 2018 Free Software Foundation, Inc.
 206 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 207 #       This is free software: you are free to change and redistribute it.
 208 #       There is NO WARRANTY, to the extent permitted by law.
 209 #
 210 #       Written by David MacKenzie and Jim Meyering.