678ab7fd8c37d79d26ad3947c408ccb393c02fa2
[BK-2020-03.git] / 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+