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README.md
90
README.md
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@ -16,7 +16,11 @@ I looked into "Shamir secret sharing" but I find that generating a new secret th
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### output:
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this bash script
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this bash script is set to take N recipients and encrypt four file to make sure only with the quorum of at least 3 recipients the file will be opened
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the logic behind that is really simple:
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### requirements:
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@ -33,3 +37,87 @@ edit the debug variable to add your email address (if you want) for debugging pu
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your output will be a file named
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your_file_to_encrypt.ext.ENCRYPTED
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### customization:
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if you want to increase the number of people needed to decrypt the file to 4 for example,
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edit this block of code from:
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```
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#main loop:
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for ((idxA=0; idxA<max; idxA++)); do # iterate idxA from 0 to length
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for ((idxB=idxA; idxB<max; idxB++)); do # iterate idxB from idxA to length
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for ((idxC=idxB; idxC<max; idxC++)); do # iterate idxC from idxB to length
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if [ "${emails[$idxA]}" == "${emails[$idxB]}" ] || [ "${emails[$idxB]}" == "${emails[$idxC]}" ] || [ "${emails[$idxA]}" == "${emails[$idxC]}" ]; then
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echo "A, B or C are the same"
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continue
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else
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#custom execution for first run:
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if [ "$counter" == 0 ]; then
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gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" "$debug" --output $workdir/$file.step$counter $file
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#custom execution for last run:
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elif [ "$counter" == $((ans-1)) ]; then
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gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" "$debug" --output $file.ENCRYPTED $workdir/$file.step$((counter-1))
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#normal execution:
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else
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gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" "$debug" --output $workdir/$file.step$counter $workdir/$file.step$((counter-1))
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fi
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#increase loop counter:
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((counter++))
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fi
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done
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done
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done
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```
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```
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#main loop:
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for ((idxA=0; idxA<max; idxA++)); do # iterate idxA from 0 to length
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for ((idxB=idxA; idxB<max; idxB++)); do # iterate idxB from idxA to length
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for ((idxC=idxB; idxC<max; idxC++)); do # iterate idxC from idxB to length
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for ((idxD=idxC; idxD<max; idxD++)); do # iterate idxD from idxC to length
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if [ "${emails[$idxA]}" == "${emails[$idxB]}" ] || [ "${emails[$idxB]}" == "${emails[$idxC]}" ] || [ "${emails[$idxA]}" == "${emails[$idxC]}" ] || [ "${emails[$idxA]}" == "${emails[$idxD]}" ] || [ "${emails[$idxB]}" == "${emails[$idxD]}" ] || [ "${emails[$idxC]}" == "${emails[$idxD]}" ]; then
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#echo "A, B, C or D are the same"
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continue
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else
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#custom execution for first run:
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if [ "$counter" == 0 ]; then
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $workdir/$file.step$counter $file"
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#custom execution for last run:
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elif [ "$counter" == $((ans-1)) ]; then
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $file.ENCRYPTED $workdir/$file.step$((counter-1))"
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#normal execution:
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else
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $workdir/$file.step$counter $workdir/$file.step$((counter-1))"
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fi
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#increase loop counter:
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((counter++))
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fi
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done
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done
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done
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done
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```
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and then adjust the variable "combinate" to 4:
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```
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combinate=4
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```
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1
file.txt
Normal file
1
file.txt
Normal file
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@ -0,0 +1 @@
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banana
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123
gpg-quorum_4of5.sh
Executable file
123
gpg-quorum_4of5.sh
Executable file
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@ -0,0 +1,123 @@
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#!/usr/bin/env bash
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#Scipt to encrypt a file with some known keys,
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#the script will combin the encryptions to ensure that a minimum quorum defined in "combinate" variable is needed to open the file.
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#the script will not auto-adjust to an arbitrary change of "combinate" since one or more loops in the main loop should be tuned,
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#right now it's adjusted ofr a quorum of 3 recipients.
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#
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#usage: gpg-quorum_3of5.sh filename_to_encrypt.ext
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#retrieve the email list
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readarray -t emails < emails.txt
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file=$1
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#debug email if you want to self-decrypt, you can also leave it blank but don't populate it without "-r":
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debug="-r youermail@provider.net"
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#counters:
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counter=0
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firstrun=0
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#minimum numbers of recipients that needs to agree to decypher the file:
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combinate=4
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#work directory:
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workdir="_WORKDIR"
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#lenght of array:
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max=${#emails[@]} # Take the length of that array
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#-----
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#CALCULATE number of combinations for our emails
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#function for factorial calculation
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function fun_fact {
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num=$1
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fact=1
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for((i=2;i<=num;i++))
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{
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fact=$((fact * i)) #fact = fact * i
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}
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echo $fact
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}
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#n is the lenght of the array
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n=$max
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#r is the number of recipients needed to open the file
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r=$combinate
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a=$( fun_fact $n )
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b=$( fun_fact $r )
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c=$(( $n - $r ))
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d=$( fun_fact $c )
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t=$(( $b * $d ))
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ans=$(( $a / $t ))
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echo "max number of combinations: "$ans
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#-----
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#create our workdir if it does not exist:
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if [ ! -d "$workdir" ]
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then
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echo "creating dir"
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mkdir $workdir
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else
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echo "Directory $workdir exists, exiting"
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exit
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fi
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#main loop:
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for ((idxA=0; idxA<max; idxA++)); do # iterate idxA from 0 to length
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for ((idxB=idxA; idxB<max; idxB++)); do # iterate idxB from idxA to length
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for ((idxC=idxB; idxC<max; idxC++)); do # iterate idxC from idxB to length
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for ((idxD=idxC; idxD<max; idxD++)); do # iterate idxD from idxC to length
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if [ "${emails[$idxA]}" == "${emails[$idxB]}" ] || [ "${emails[$idxB]}" == "${emails[$idxC]}" ] || [ "${emails[$idxA]}" == "${emails[$idxC]}" ] || [ "${emails[$idxA]}" == "${emails[$idxD]}" ] || [ "${emails[$idxB]}" == "${emails[$idxD]}" ] || [ "${emails[$idxC]}" == "${emails[$idxD]}" ]; then
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#echo "A, B, C or D are the same"
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continue
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else
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#custom execution for first run:
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if [ "$counter" == 0 ]; then
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $workdir/$file.step$counter $file"
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#custom execution for last run:
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elif [ "$counter" == $((ans-1)) ]; then
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $file.ENCRYPTED $workdir/$file.step$((counter-1))"
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#normal execution:
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else
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echo "gpg -ea -r "${emails[$idxA]}" -r "${emails[$idxB]}" -r "${emails[$idxC]}" -r "${emails[$idxD]}" "$debug" --output $workdir/$file.step$counter $workdir/$file.step$((counter-1))"
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fi
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#increase loop counter:
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((counter++))
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fi
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done
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done
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done
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done
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#remove work directory:
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rm -rf $workdir
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#the combination matrix for a quorum of 3 recipients on 5:
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#recipients: A,B,C,D,E
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#
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#A,B,C
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#A,B,D
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#A,B,E
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#A,C,D
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#A,C,E
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#A,D,E
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#B,C,D
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#B,C,E
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#B,D,E
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#C,D,E
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#SOURCES:
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#http://www.anonhack.in/2018/05/program-to-calculate-combination-ncr-in-bash-shell-scripting/
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#https://www.log2base2.com/shell-script-examples/loop/shell-script-to-find-factorial-of-a-number.html
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