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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. |