| 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 |
| 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 20` generates a 20-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". |
| 107 | # Note: This particular example float should be rounded to "22" later. |
| 108 | |
| 109 | # Round $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions. |
| 110 | # Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html |
| 111 | CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}') |
| 112 | |
| 113 | # Generate passphrase |
| 114 | PASS1=$(rpass "$CHAR_COUNT1") |
| 115 | echo -e "$PASS1" |
| 116 | |
| 117 | |
| 118 | #==References== |
| 119 | # |
| 120 | # - How to echo a string as stderr instead of stdout. |
| 121 | # https://stackoverflow.com/a/2990533 |
| 122 | # Author: James Roth |
| 123 | # Date: 2010-06-07T14:52Z |
| 124 | # Date Accessed: 2020-01-20 |
| 125 | # |
| 126 | # - How to check if script argument exists or not. |
| 127 | # https://stackoverflow.com/a/6482403 |
| 128 | # Author: phoxix |
| 129 | # Date: 2011-06-26T05:55Z |
| 130 | # Date Accessed: 2020-01-20 |
| 131 | # |
| 132 | # - How to check that a string is an integer using regular expression test. |
| 133 | # https://stackoverflow.com/a/806923 |
| 134 | # Author: Charles Duffy |
| 135 | # Date: 2009-04-30T13:32Z |
| 136 | # Date Accessed: 2020-01-20 |
| 137 | # |
| 138 | # - How to use `bc` to calculate logarithms in Bash |
| 139 | # http://phodd.net/gnu-bc/bcfaq.html#bashlog |
| 140 | # Author: unknown |
| 141 | # Date Accessed: 2020-01-20 |
| 142 | # |
| 143 | # - How to use `awk` to convert and round up a float to an integer. |
| 144 | # https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html |
| 145 | # Author: Md. Minhazul Haque |
| 146 | # Date: 2015-01-09 |
| 147 | # Date Accessed: 2020-01-20 |
| 148 | # |
| 149 | # - How to use `/dev/urandom`, `tr`, and `head` to generate a random password in Bash. |
| 150 | # https://www.thegeekstuff.com/2010/04/unix-bash-function-examples/ |
| 151 | # Author: SASIKALA, Ramesh Natarajan |
| 152 | # Date: 2010-04-21 |
| 153 | # Date Accessed: 2020-01-20 |
| 154 | # |
| 155 | # - Bech32 base32 charset |
| 156 | # https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki |
| 157 | # Author: Pieter Wuille <pieter.wuille@gmail.com> |
| 158 | # Date: 2017-03-20 |
| 159 | # License: BSD-2-Clause |
| 160 | # Date: Accessed: 2021-01-23 |
| 161 | # |
| 162 | # - Dependencies: bash, echo, bc, awk, tr, head. |
| 163 | # |
| 164 | # - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu) |
| 165 | # Copyright (C) 2019 Free Software Foundation, Inc. |
| 166 | # License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> |
| 167 | # This is free software; you are free to change and redistribute it. |
| 168 | # There is NO WARRANTY, to the extent permitted by law. |
| 169 | # |
| 170 | # - echo (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 Brian Fox and Chet Ramey. |
| 177 | # |
| 178 | # - bc 1.07.1 |
| 179 | # Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc. |
| 180 | # |
| 181 | # - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2) |
| 182 | # Copyright (C) 1989, 1991-2018 Free Software Foundation. |
| 183 | # |
| 184 | # This program is free software; you can redistribute it and/or modify |
| 185 | # it under the terms of the GNU General Public License as published by |
| 186 | # the Free Software Foundation; either version 3 of the License, or |
| 187 | # (at your option) any later version. |
| 188 | # |
| 189 | # This program is distributed in the hope that it will be useful, |
| 190 | # but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 191 | # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 192 | # GNU General Public License for more details. |
| 193 | # |
| 194 | # You should have received a copy of the GNU General Public License |
| 195 | # along with this program. If not, see http://www.gnu.org/licenses/. |
| 196 | # |
| 197 | # - tr (GNU coreutils) 8.30 |
| 198 | # Copyright (C) 2018 Free Software Foundation, Inc. |
| 199 | # License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. |
| 200 | # This is free software: you are free to change and redistribute it. |
| 201 | # There is NO WARRANTY, to the extent permitted by law. |
| 202 | # |
| 203 | # Written by Jim Meyering. |
| 204 | # |
| 205 | # - head (GNU coreutils) 8.30 |
| 206 | # Copyright (C) 2018 Free Software Foundation, Inc. |
| 207 | # License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. |
| 208 | # This is free software: you are free to change and redistribute it. |
| 209 | # There is NO WARRANTY, to the extent permitted by law. |
| 210 | # |
| 211 | # Written by David MacKenzie and Jim Meyering. |