Encode a string for use in macOS /etc/kcpassword using shell, printf, sed, awk and xxd

kcpasswordEncode.sh

#!/bin/bash
#kcpasswordEncode (20210911) Copyright (c) 2021 Joel Bruner (https://github.com/brunerd)
#Licensed under the MIT License

#given a string creates data for /etc/kcpassword
function kcpasswordEncode {

	#ascii string
	local thisString="${1}"
	local i

	#macOS cipher hex ascii representation array
	local cipherHex_array=( 7D 89 52 23 D2 BC DD EA A3 B9 1F )

	#converted to hex representation with spaces
	local thisStringHex_array=( $(echo -n "${thisString}" | xxd -p -u | sed 's/../& /g') )

	#get padding by subtraction if under 12 
	if [ "${#thisStringHex_array[@]}" -lt 12  ]; then
		local padding=$(( 12 -  ${#thisStringHex_array[@]} ))
	#get padding by subtracting remainder of modulo 12 if over 12 
	elif [ "$(( ${#thisStringHex_array[@]} % 12 ))" -ne 0  ]; then
		local padding=$(( (12 - ${#thisStringHex_array[@]} % 12) ))
	#otherwise even multiples of 12 still need 12 padding
	else
		local padding=12
	fi	

	#cycle through each element of the array + padding
	for ((i=0; i < $(( ${#thisStringHex_array[@]} + ${padding})); i++)); do
		#use modulus to loop through the cipher array elements
		local charHex_cipher=${cipherHex_array[$(( $i % 11 ))]}

		#get the current hex representation element
		local charHex=${thisStringHex_array[$i]}
	
		#use $(( shell Aritmethic )) to ^ XOR the two 0x## values (extra padding is 0x00) 
		#take decimal value and printf convert to two char hex value
		#use xxd to convert hex to actual value and append to the encodedString variable
		local encodedString+=$(printf "%02X" "$(( 0x${charHex_cipher} ^ 0x${charHex:-00} ))" | xxd -r -p)
	done

	#return the string without a newline
	echo -n "${encodedString}"
}


#this just echoes it out use, does not write the file nor enable plist (see my setAutoLogin for that)
kcpasswordEncode "${1}"