// asymmetric - crypto_box_easy is easy but it's not asymmetric, in that
// Alice can also decrpt things encrypted to Bob
//
//   CFLAGS=`pkg-config --cflags --libs libsodium` make asymmetric
//   ./asymmetric

#include <err.h>
#include <sodium.h>

#define MESSAGE (const unsigned char *) "blub"
#define MESSAGE_LEN 4
#define CIPHERTEXT_LEN (crypto_box_MACBYTES + MESSAGE_LEN)

int
main(int argc, char *argv[])
{
	unsigned char alice_pub[crypto_box_PUBLICKEYBYTES];
	unsigned char bobby_pub[crypto_box_PUBLICKEYBYTES];
	unsigned char alice_key[crypto_box_SECRETKEYBYTES];
	unsigned char bobby_key[crypto_box_SECRETKEYBYTES];

	if (sodium_init()) err(1, "sodium_init");

	if (crypto_box_keypair(alice_pub, alice_key))
		errx(1, "crypto_box_keypair");
	if (crypto_box_keypair(bobby_pub, bobby_key))
		errx(1, "crypto_box_keypair");

	unsigned char nonce[crypto_box_NONCEBYTES];
	randombytes_buf(nonce, sizeof nonce);

	unsigned char ciphertext[CIPHERTEXT_LEN];
	unsigned char decrypted[MESSAGE_LEN];

	if (crypto_box_easy(ciphertext, MESSAGE, MESSAGE_LEN, nonce, bobby_pub,
	                    alice_key))
		errx(1, "crypto_box_easy");

	if (crypto_box_open_easy(decrypted, ciphertext, CIPHERTEXT_LEN, nonce,
	                         alice_pub, bobby_key)) {
		errx(1, "crypto_box_open_easy");
	}
	printf("%.*s\n", MESSAGE_LEN, decrypted);
	// but can Alice also read it? yes!
	if (crypto_box_open_easy(decrypted, ciphertext, CIPHERTEXT_LEN, nonce,
	                         bobby_pub, alice_key)) {
		errx(1, "crypto_box_open_easy");
	}
	printf("%.*s\n", MESSAGE_LEN, decrypted);
}