n2n/header_encryption.c

#include <stdio.h>
#include <stdint.h>

// #include "n2n_wire.h"	// n2n_community_t
#include "n2n.h"
#include "speck.h"
#include "portable_endian.h"


uint32_t decryt_packet_header (uint8_t packet[], uint8_t packet_len,
			       char * community_name, speck_ctx * ctx) {

	// assemble IV
	// the last four are ASCII "n2n!" and do not get overwritten
	uint8_t iv[16] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			   0x00, 0x00, 0x00, 0x00, 0x6E, 0x32, 0x6E, 0x21 };
	// the first 96 bits of the packet are used padded with ASCII "n2n!"
	// to full 128 bit IV
	memcopy (iv, packet, 12);

	// alternatively, consider: pearson_hash_128 (iv, packet, 12)

	// try community name as possible key and check for magic bytes
	uint32_t magic = 0x6E326E00; // ="n2n_"
	uint32_t test_magic;
	// check for magic bytes and resonable value in header len field
	speck_he ((uint8_t*)&test_magic, &packet[12], 4, iv, ctx);
	test_magic = be32toh (test_magic);
	if ( ((test_magic <<  8) == magic)
	  && ((test_magic >> 24) <= packet_len) // (test_masgic >> 24) is header_len
	   ) {
		speck_he (&packet[12], &packet[12], (test_magic >> 24) - 12, iv, ctx);
		// restore original packet order
		memcpy (&packet[0], &packet[16], 4);
		memcpy (&packet[4], community_name, N2N_COMMUNITY_SIZE);
		return (1); // successful
	} else
		return (0); // unsuccessful
}


int32_t decryt_packet_header_if_required (uint8_t packet[], uint16_t packet_len,
					   struct sn_community *communities) {

	if (packet_len < 20)
		return (-1);

	// first, check if header is unenrypted to put it into the fast-lane then

	// the following check is around 99.99962 percent reliable
	// it heavily relies on the structure of packet's common part
	// changes to wire.c:encode/decode_common need to go together with this code
	if ( (packet[19] == (uint8_t)0x00)	// null terminated community name
	  && (packet[00] == N2N_PKT_VERSION)	// correct packet version
//	  && (packet[01] <= N2N_DEFAULT_TTL) 	// reasonable TTL -- might interfere with hole-punching-related or cli passed higher values ?!
	  && ((be16toh (*(uint16_t*)&(packet[02])) & N2N_FLAGS_TYPE_MASK ) <= MSG_TYPE_MAX_TYPE  ) // message type
	  && ( be16toh (*(uint16_t*)&(packet[02])) < N2N_FLAGS_OPTIONS)	// flags
	   ) {

		// most probably unencrypted
		return (1);

	} else {

		// most probably encrypted
		// cycle through the known communities (as keys) to eventually decrypt
		int32_t ret;
		struct sn_community *c, *tmp;
		HASH_ITER (hh, communities, c, tmp) {
			// check if this is an encrypted community
			if ( ret = decrypt_packet_header (packet, packet_len, c->community, c-> ctx) ) {
				// no upgrade from unencrypted to encrypted
				if (c->header_encryption == 1)
					return (-2);
				// set to 'encrypted'
				 c->header_encryption = 2;
				// no need to test any further
				return (2);
			}
		}
		// no match
		return (-3);
	}
}


int32_t encryt_packet_header (uint8_t packet[], uint8_t header_len, speck_ctx * ctx) {

	if (header_len < 20)
		return (-1);

	memcpy (&packet[16], &packet[00], 4);

	uint8_t iv[16];
	((uint64_t*)iv)[0] = n2n_rand ();
	((uint64_t*)iv)[1] = n2n_rand ();

	const uint32_t magic = 0x006E326E;
	((uint32_t*)iv)[3] = htobe32 (magic);

	iv[12] = header_len;

	speck_he (&packet[12], &packet[12], header_len - 12, iv, ctx);
}