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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
59let ALPHABET_SIZE="26+26+10" # number of unique chars in [:alnum:], argument fed to `tr -c` in 'Generate passphrase' step)
60LOG_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
64function 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/
70function 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
79if [ -z "$1" ]
80then
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
85else
86 ENTROPY_BIT_COUNT1="$1"
87fi
88
89# Check if $ENTROPY_BIT_COUNT1 is an non-negative integer
90 # Note: Regular expression test is adapted from https://stackoverflow.com/a/806923
91RETEST1='^[0-9]+$'
92if ! [[ $ENTROPY_BIT_COUNT1 =~ $RETEST1 ]] ; then
93 echo "error: Not an integer." >&2; exit 1
94fi
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
102CHAR_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 $CHAR_COUNT1_FLOAT1 up to next highest integer for use as argument in later bash functions.
106 # Note: awk expression from https://bits.mdminhazulhaque.io/linux/round-number-in-bash-script.html
107CHAR_COUNT1=$(echo "$CHAR_COUNT1_FLOAT" | awk '{print ($0-int($0)>0)?int($0)+1:int($0)}')
108
109# Generate passphrase
110PASS1=$(rpass "$CHAR_COUNT1")
111echo -e "$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.