Generate wireguard public and private key with openssl and bash

keygen.sh

#!/bin/bash

# This is used by openssl to tell the type of the key
private_head="MC4CAQAwBQYDK2VuBCIEIA=="
public_head="MCowBQYDK2VuAyEA"


# generate one string (containing '\x0') from two base64 
b64join() {
	echo -e "$(printf ${1} \
		| base64 -d \
		| sed -e 's/\x0/whatsup/g')$(printf ${2} \
		| base64 -d \
		| sed -e 's/\x0/whatsup/g')" \
	| sed -e "s/whatsup/\x0/g"
}


case ${1} in
	genkey)
		openssl genpkey -algorithm X25519 -outform der \
		| tail -c 32 \
		| base64 \
		;;
	pubkey)
		b64join ${private_head} ${2} \
		| openssl pkey -inform DER -outform DER -pubout \
		| tail -c 32 \
		| base64
		;;
	exchange)
		openssl pkeyutl -derive \
			-keyform DER -inkey <(b64join ${private_head} ${2}) \
			-peerform DER -peerkey <(b64join ${public_head} ${3} | sed 's/K$/=/') \
		| base64
		;;
esac