src/common/f8.c

#include "f8.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>



/* The code has been referred from
 *
 * 1.https://www.gsma.com/aboutus/wp-content/uploads/2014/12/uea2uia2d1v21.pdf
 * 2.https://www.gsma.com/aboutus/wp-content/uploads/2014/12/snow3gspec.pdf
 *
 */



/* f8.
 * Input key: 128 bit Confidentiality Key.
 * Input count:32-bit Count, Frame dependent input.
 * Input bearer: 5-bit Bearer identity (in the LSB side).
 * Input dir:1 bit, direction of transmission.
 * Input data: length number of bits, input bit stream.
 * Input length: 32 bit Length, i.e., the number of bits to be encrypted or
 * decrypted.
 * Output data: Output bit stream. Assumes data is suitably memory
 * allocated.
 * Encrypts/decrypts blocks of data between 1 and 2^32 bits in length as
 * defined in Section 3.
 */

void f8( u8 *key, u32 count, u32 bearer, u32 dir, u8 *data, u32 length )
{
	u32 K[4],IV[4];
	int n = ( length + 31 ) / 32;
	int i=0;
	u32 *KS;

	/*Initialisation*/

	/* Load the confidentiality key for SNOW 3G initialization as in section
		3.4.(https://www.gsma.com/aboutus/wp-content/uploads/2014/12/snow3gspec.pdf)
	*/

	for (i=0; i<4; i++)
		K[3-i] = (key[4*i] << 24) ^ (key[4*i+1] << 16) ^ (key[4*i+2] << 8) ^
		(key[4*i+3]);

	/* Prepare the initialization vector (IV) for SNOW 3G initialization as in
	section 3.4.(https://www.gsma.com/aboutus/wp-content/uploads/2014/12/snow3gspec.pdf) */


	IV[3] = count;
	IV[2] = (bearer << 27) | ((dir & 0x1) << 26);
	IV[1] = IV[3];
	IV[0] = IV[2];

	/* Run SNOW 3G algorithm to generate sequence of key stream bits KS*/

	Initialize(K,IV);
	KS = (u32 *)malloc(4*n);
	GenerateKeystream(n,(u32*)KS);

	/* Exclusive-OR the input data with keystream to generate the output bit
	stream */

	for (i=0; i<n; i++)
	{
		data[4*i+0] ^= (u8) (KS[i] >> 24) & 0xff;
		data[4*i+1] ^= (u8) (KS[i] >> 16) & 0xff;
		data[4*i+2] ^= (u8) (KS[i] >> 8) & 0xff;
		data[4*i+3] ^= (u8) (KS[i] ) & 0xff;
	}

	free(KS);

}
/* End of f8.c */