69 lines
1.7 KiB
Text
69 lines
1.7 KiB
Text
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#!/usr/bin/env zsh
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#
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# Usage: genpass-xkcd [NUM]
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#
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# Generate a password made of words from /usr/share/dict/words
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# with the security margin of at least 128 bits.
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#
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# Example password: 9-mien-flood-Patti-buxom-dozes-ickier-pay-ailed-Foster
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#
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# If given a numerical argument, generate that many passwords.
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#
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# The name of this utility is a reference to https://xkcd.com/936/.
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emulate -L zsh -o no_unset -o warn_create_global -o warn_nested_var -o extended_glob
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if [[ ARGC -gt 1 || ${1-1} != ${~:-<1-$((16#7FFFFFFF))>} ]]; then
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print -ru2 -- "usage: $0 [NUM]"
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return 1
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fi
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zmodload zsh/system zsh/mathfunc || return
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local -r dict=/usr/share/dict/words
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if [[ ! -e $dict ]]; then
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print -ru2 -- "$0: file not found: $dict"
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return 1
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fi
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# Read all dictionary words and leave only those made of 1-6 characters.
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local -a words
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words=(${(M)${(f)"$(<$dict)"}:#[a-zA-Z](#c1,6)}) || return
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if (( $#words < 2 )); then
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print -ru2 -- "$0: not enough suitable words in $dict"
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return 1
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fi
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if (( $#words > 16#7FFFFFFF )); then
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print -ru2 -- "$0: too many words in $dict"
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return 1
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fi
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# Figure out how many words we need for 128 bits of security margin.
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# Each word adds log2($#words) bits.
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local -i n=$((ceil(128. / (log($#words) / log(2)))))
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{
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local c
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repeat ${1-1}; do
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print -rn -- $n
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repeat $n; do
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while true; do
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# Generate a random number in [0, 2**31).
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local -i rnd=0
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repeat 4; do
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sysread -s1 c || return
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(( rnd = (~(1 << 23) & rnd) << 8 | #c ))
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done
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# Avoid bias towards words in the beginning of the list.
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(( rnd < 16#7FFFFFFF / $#words * $#words )) || continue
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print -rn -- -$words[rnd%$#words+1]
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break
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done
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done
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print
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done
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} </dev/urandom
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