unitproc/bknpass

   1 #!/bin/bash
   2
   3 # Date: 2020-01-20T16:34Z
   4 #
   5 # Author: Steven Baltakatei Sandoval (baltakatei.com)
   6 #
   7 # License: This bash script, `bknpass`, is licensed under GPLv3 or
   8 # later by Steven Baltakatei Sandoval:
   9 #
  10 #    `bknpass`, an alphanumeric password generator
  11 #    Copyright (C) 2020  Steven Baltakatei Sandoval (baltakatei.com)
  12 #
  13 #    This program is free software: you can redistribute it and/or modify
  14 #    it under the terms of the GNU General Public License as published by
  15 #    the Free Software Foundation, either version 3 of the License, or
  16 #    any later version.
  17 #
  18 #    This program is distributed in the hope that it will be useful,
  19 #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  20 #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21 #    GNU General Public License for more details.
  22 #
  23 #    A copy of the GNU General Public License may be found at
  24 #    <https://www.gnu.org/licenses/>.
  25 #
  26 # Description: This bash script generates alphanumeric passphrases
  27 # with a char-count determined by a user-provided number of bits of
  28 # entropy. The passphrase is then outputted to stdout with a trailing
  29 # newline. It works as follows:
  30 #
  31 #   - Prompt user for an integer. This integer is the number of bits
  32 #     of entropy that the generated password should have.
  33 #
  34 #   - Check if user-provided string is an integer using `bash` regular
  35 #     expression test.
  36 #
  37 #   - Calculate the minimum number of alphanumeric characters required
  38 #     to encode the specified number of bits of entropy.
  39 #
  40 #       - This step uses `bc` to calculate a logarithm float string
  41 #         and `awk` to convert the float into an integer, rounding up.
  42 #
  43 #   - Use `tr`, `/dev/urandom`, and `head` to generate a random
  44 #     alphanumeric string with the length calculated in the previous
  45 #     step.
  46 #
  47 #   - Use `echo` to display the passphrase in stdout with a trailing
  48 #     newline.
  49 #
  50 # Dependencies: bash, echo, bc, awk, tr, head. See end of file
  51 #
  52 # Tested on:
  53 #
  54 #   - GNU/Linux Debian 10
  55
  56
  57 #==Initialization==
  58
  59 let ALPHABET_SIZE="26+26+10" # number of unique chars in [:alnum:], argument fed to `tr -c` in 'Generate passphrase' step)
  60 LOG_BASE=2 # Set logarithm base to 2
  61
  62 # Define `echoerr` function which outputs text to stderr
  63     # Note: function copied from https://stackoverflow.com/a/2990533
  64 function echoerr {
  65     echo "$@" 1>&2;
  66 }
  67
  68 # Define `rpass` function which generates an alphanumeric passphrase of length $1 (ex: `rpass 22` generates a 22-char string)
  69     # Note: function adapted from https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
  70 function rpass {
  71     cat /dev/urandom | LC_ALL=C tr -cd "[:alnum:]" | head -c ${1:-22}
  72 }
  73
  74
  75 #==Main Program==
  76
  77 # Define $ENTROPY_BIT_COUNT1 as argument $1 or prompt user if $1 is not defined.
  78     # note: argument test adapted from https://stackoverflow.com/a/6482403
  79 if [ -z "$1" ]
  80 then
  81     echo "Entropy bit count argument (\$1) not supplied."
  82     # Get from user the number of bits of entropy.
  83     echoerr -n "Please specify the required strength of the password in bits of entropy (ex: 256):" # prompt via stderr
  84     read ENTROPY_BIT_COUNT1
  85 else
  86     ENTROPY_BIT_COUNT1="$1"
  87 fi
  88
  89 # Check if $ENTROPY_BIT_COUNT1 is an non-negative integer
  90     # Note: Regular expression test is adapted from https://stackoverflow.com/a/806923
  91 RETEST1='^[0-9]+$'
  92 if ! [[ $ENTROPY_BIT_COUNT1 =~ $RETEST1 ]] ; then
  93    echo "error: Not an integer." >&2; exit 1
  94 fi
  95
  96 # Calculate minimum count of chars needed to encode $ENTROPY_BIT_COUNT1 with alphabet size of $ALPHABET_SIZE as float
  97     # Solve ln(a^n)/ln(2)=b for n using `bc` where
  98       # a=$ALPHABET_SIZE
  99       # n=$CHAR_COUNT1_FLOAT
 100       # b=$ENTROPY_BIT_COUNT1
 101     # Note: `bc` logarithm usage adapted from http://phodd.net/gnu-bc/bcfaq.html#bashlog
 102 CHAR_COUNT1_FLOAT=$(echo "$ENTROPY_BIT_COUNT1*l($LOG_BASE)/l($ALPHABET_SIZE)" | bc -l)
 103     # Note: Float will be of form "21.49744370650136860806". This particular float should be rounded to "22" later.
 104
 105 # Round $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions.
 106     # Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
 107 CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')
 108
 109 # Generate passphrase
 110 PASS1=$(rpass "$CHAR_COUNT1")
 111 echo -e "$PASS1"
 112
 113
 114 #==References==
 115 #
 116 # - How to echo a string as stderr instead of stdout.
 117 #   https://stackoverflow.com/a/2990533
 118 #   Author: James Roth
 119 #   Date: 2010-06-07T14:52Z
 120 #   Date Accessed: 2020-01-20
 121 #
 122 # - How to check if script argument exists or not.
 123 #   https://stackoverflow.com/a/6482403
 124 #   Author: phoxix
 125 #   Date: 2011-06-26T05:55Z
 126 #   Date Accessed: 2020-01-20
 127 #
 128 # - How to check that a string is an integer using regular expression test.
 129 #   https://stackoverflow.com/a/806923
 130 #   Author: Charles Duffy
 131 #   Date: 2009-04-30T13:32Z
 132 #   Date Accessed: 2020-01-20
 133 #
 134 # - How to use `bc` to calculate logarithms in Bash
 135 #   http://phodd.net/gnu-bc/bcfaq.html#bashlog
 136 #   Author: unknown
 137 #   Date Accessed: 2020-01-20
 138 #
 139 # - How to use `awk` to convert and round up a float to an integer.
 140 #   https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
 141 #   Author: Md. Minhazul Haque
 142 #   Date: 2015-01-09
 143 #   Date Accessed: 2020-01-20
 144 #
 145 # - How to use `/dev/urandom`, `tr`, and `head` to generate a random password in Bash.
 146 #   https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
 147 #   Author: SASIKALA, Ramesh Natarajan
 148 #   Date: 2010-04-21
 149 #   Date Accessed: 2020-01-20
 150 #
 151 # - Dependencies: bash, echo, bc, awk, tr, head.
 152 #
 153 #     - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)
 154 #       Copyright (C) 2019 Free Software Foundation, Inc.
 155 #       License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 156 #       This is free software; you are free to change and redistribute it.
 157 #       There is NO WARRANTY, to the extent permitted by law.
 158 #
 159 #     - echo (GNU coreutils) 8.30
 160 #       Copyright (C) 2018 Free Software Foundation, Inc.
 161 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 162 #       This is free software: you are free to change and redistribute it.
 163 #       There is NO WARRANTY, to the extent permitted by law.
 164 #
 165 #       Written by Brian Fox and Chet Ramey.
 166 #
 167 #     - bc 1.07.1
 168 #       Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
 169 #
 170 #     - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
 171 #       Copyright (C) 1989, 1991-2018 Free Software Foundation.
 172 #
 173 #       This program is free software; you can redistribute it and/or modify
 174 #       it under the terms of the GNU General Public License as published by
 175 #       the Free Software Foundation; either version 3 of the License, or
 176 #       (at your option) any later version.
 177 #
 178 #       This program is distributed in the hope that it will be useful,
 179 #       but WITHOUT ANY WARRANTY; without even the implied warranty of
 180 #       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 181 #       GNU General Public License for more details.
 182 #
 183 #       You should have received a copy of the GNU General Public License
 184 #       along with this program. If not, see http://www.gnu.org/licenses/.
 185 #
 186 #     - tr (GNU coreutils) 8.30
 187 #       Copyright (C) 2018 Free Software Foundation, Inc.
 188 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 189 #       This is free software: you are free to change and redistribute it.
 190 #       There is NO WARRANTY, to the extent permitted by law.
 191 #
 192 #       Written by Jim Meyering.
 193 #
 194 #     - head (GNU coreutils) 8.30
 195 #       Copyright (C) 2018 Free Software Foundation, Inc.
 196 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 197 #       This is free software: you are free to change and redistribute it.
 198 #       There is NO WARRANTY, to the extent permitted by law.
 199 #
 200 #       Written by David MacKenzie and Jim Meyering.