user/bknpass

   1 #!/bin/bash
   2 # Desc: Generate alphanumeric passphrase with specified bits of entropy.
   3 # Usage: bknpass [int]
   4 # Example: bknpass 128
   5 # Depends: bash, echo, bc, awk, tr, head, Debian 10
   6 # Version: 0.1.0
   7 # Note: This bash script generates alphanumeric passphrases
   8 #   with a char-count determined by a user-provided number of bits of
   9 #   entropy. The passphrase is then outputted to stdout with a trailing
  10 #   newline. It works as follows:
  11 #
  12 #     - Prompt user for an integer. This integer is the number of bits
  13 #       of entropy that the generated password should have.
  14 #
  15 #     - Check if user-provided string is an integer using `bash` regular
  16 #       expression test.
  17 #
  18 #     - Calculate the minimum number of bech32 base32 characters
  19 #       required to encode the specified number of bits of entropy.
  20 #
  21 #         - This step uses `bc` to calculate a logarithm float string
  22 #           and `awk` to convert the float into an integer, rounding up.
  23 #
  24 #     - Use `tr`, `/dev/urandom`, and `head` to generate a random
  25 #       alphanumeric string with the length calculated in the previous
  26 #       step.
  27 #
  28 #     - Use `echo` to display the passphrase in stdout with a trailing
  29 #       newline.
  30
  31
  32 #==Initialization==
  33
  34 let ALPHABET_SIZE="32" # number of unique chars in bech32 base32 charset
  35 LOG_BASE=2 # Set logarithm base to 2
  36
  37 # Define `echoerr` function which outputs text to stderr
  38     # Note: function copied from https://stackoverflow.com/a/2990533
  39 function echoerr {
  40     echo "$@" 1>&2;
  41 }
  42
  43 # Define `rpass` function which generates a base32 passphrase of length $1 (ex: `rpass 20` generates a 20-char string)
  44 #   Note: function adapted from https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
  45 #   Note: base32 charset uses bech32 charset
  46 function rpass {
  47     cat /dev/urandom | LC_ALL=C tr -cd "qpzry9x8gf2tvdw0s3jn54khce6mua7l" | head -c ${1:-22}
  48 }
  49
  50
  51 #==Main Program==
  52
  53 # Define $ENTROPY_BIT_COUNT1 as argument $1 or prompt user if $1 is not defined.
  54 #     Note: argument test adapted from https://stackoverflow.com/a/6482403
  55 if [ -z "$1" ]
  56 then
  57     echo "Entropy bit count argument (\$1) not supplied."
  58     # Get from user the number of bits of entropy.
  59     echoerr -n "Please specify the required strength of the password in bits of entropy (ex: 256):" # prompt via stderr
  60     read ENTROPY_BIT_COUNT1
  61 else
  62     ENTROPY_BIT_COUNT1="$1"
  63 fi
  64
  65 # Check if $ENTROPY_BIT_COUNT1 is an non-negative integer
  66 #     Note: Regular expression test is adapted from https://stackoverflow.com/a/806923
  67 RETEST1='^[0-9]+$'
  68 if ! [[ $ENTROPY_BIT_COUNT1 =~ $RETEST1 ]] ; then
  69    echo "error: Not an integer." >&2; exit 1
  70 fi
  71
  72 # Calculate minimum count of chars needed to encode $ENTROPY_BIT_COUNT1 with alphabet size of $ALPHABET_SIZE as float
  73 #     Solve ln(a^n)/ln(2)=b for n using `bc` where
  74 #       a=$ALPHABET_SIZE
  75 #       n=$CHAR_COUNT1_FLOAT
  76 #       b=$ENTROPY_BIT_COUNT1
  77 #     Note: `bc` logarithm usage adapted from http://phodd.net/gnu-bc/bcfaq.html#bashlog
  78 CHAR_COUNT1_FLOAT=$(echo "$ENTROPY_BIT_COUNT1*l($LOG_BASE)/l($ALPHABET_SIZE)" | bc -l)
  79 #     Note: Float will be of form "21.49744370650136860806".
  80 #     Note: This particular example float should be rounded to "22" later.
  81
  82 # Round $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions.
  83 #     Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
  84 CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')
  85
  86 # Generate passphrase
  87 PASS1=$(rpass "$CHAR_COUNT1")
  88 echo -e "$PASS1"
  89
  90
  91 #==References==
  92 #
  93 # - How to echo a string as stderr instead of stdout.
  94 #   https://stackoverflow.com/a/2990533
  95 #   Author: James Roth
  96 #   Date: 2010-06-07T14:52Z
  97 #   Date Accessed: 2020-01-20
  98 #
  99 # - How to check if script argument exists or not.
 100 #   https://stackoverflow.com/a/6482403
 101 #   Author: phoxix
 102 #   Date: 2011-06-26T05:55Z
 103 #   Date Accessed: 2020-01-20
 104 #
 105 # - How to check that a string is an integer using regular expression test.
 106 #   https://stackoverflow.com/a/806923
 107 #   Author: Charles Duffy
 108 #   Date: 2009-04-30T13:32Z
 109 #   Date Accessed: 2020-01-20
 110 #
 111 # - How to use `bc` to calculate logarithms in Bash
 112 #   http://phodd.net/gnu-bc/bcfaq.html#bashlog
 113 #   Author: unknown
 114 #   Date Accessed: 2020-01-20
 115 #
 116 # - How to use `awk` to convert and round up a float to an integer.
 117 #   https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
 118 #   Author: Md. Minhazul Haque
 119 #   Date: 2015-01-09
 120 #   Date Accessed: 2020-01-20
 121 #
 122 # - How to use `/dev/urandom`, `tr`, and `head` to generate a random password in Bash.
 123 #   https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/
 124 #   Author: SASIKALA, Ramesh Natarajan
 125 #   Date: 2010-04-21
 126 #   Date Accessed: 2020-01-20
 127 #
 128 # - Bech32 base32 charset
 129 #   https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
 130 #   Author: Pieter Wuille <pieter.wuille@gmail.com>
 131 #   Date: 2017-03-20
 132 #   License: BSD-2-Clause
 133 #   Date: Accessed: 2021-01-23
 134 #
 135 # - Dependencies: bash, echo, bc, awk, tr, head.
 136 #
 137 #     - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)
 138 #       Copyright (C) 2019 Free Software Foundation, Inc.
 139 #       License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 140 #       This is free software; you are free to change and redistribute it.
 141 #       There is NO WARRANTY, to the extent permitted by law.
 142 #
 143 #     - echo (GNU coreutils) 8.30
 144 #       Copyright (C) 2018 Free Software Foundation, Inc.
 145 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 146 #       This is free software: you are free to change and redistribute it.
 147 #       There is NO WARRANTY, to the extent permitted by law.
 148 #
 149 #       Written by Brian Fox and Chet Ramey.
 150 #
 151 #     - bc 1.07.1
 152 #       Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
 153 #
 154 #     - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
 155 #       Copyright (C) 1989, 1991-2018 Free Software Foundation.
 156 #
 157 #       This program is free software; you can redistribute it and/or modify
 158 #       it under the terms of the GNU General Public License as published by
 159 #       the Free Software Foundation; either version 3 of the License, or
 160 #       (at your option) any later version.
 161 #
 162 #       This program is distributed in the hope that it will be useful,
 163 #       but WITHOUT ANY WARRANTY; without even the implied warranty of
 164 #       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 165 #       GNU General Public License for more details.
 166 #
 167 #       You should have received a copy of the GNU General Public License
 168 #       along with this program. If not, see http://www.gnu.org/licenses/.
 169 #
 170 #     - tr (GNU coreutils) 8.30
 171 #       Copyright (C) 2018 Free Software Foundation, Inc.
 172 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 173 #       This is free software: you are free to change and redistribute it.
 174 #       There is NO WARRANTY, to the extent permitted by law.
 175 #
 176 #       Written by Jim Meyering.
 177 #
 178 #     - head (GNU coreutils) 8.30
 179 #       Copyright (C) 2018 Free Software Foundation, Inc.
 180 #       License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
 181 #       This is free software: you are free to change and redistribute it.
 182 #       There is NO WARRANTY, to the extent permitted by law.
 183 #
 184 #       Written by David MacKenzie and Jim Meyering.
 185
 186 # Author: Steven Baltakatei Sandoval
 187 # License: GPLv3+