/* crypto/aes/aes_ctr.c -*- mode:C; c-file-style: "eay" -*- */

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#ifndef AES_DEBUG

# ifndef NDEBUG

#  define NDEBUG

# endif

#endif

#include <assert.h>

#include <openssl/aes.h>

#include "aes_locl.h"

/* NOTE: the IV/counter CTR mode is big-endian.  The rest of the AES code

 * is endian-neutral. */

/* increment counter (128-bit int) by 1 */

static void AES_ctr128_inc(unsigned char *counter) {

	unsigned long c;

	/* Grab bottom dword of counter and increment */

	c = GETU32(counter + 12);

	c++;	c &= 0xFFFFFFFF;

	PUTU32(counter + 12, c);

	/* if no overflow, we're done */

	if (c)

		return;

	/* Grab 1st dword of counter and increment */

	c = GETU32(counter +  8);

	c++;	c &= 0xFFFFFFFF;

	PUTU32(counter +  8, c);

	/* if no overflow, we're done */

	if (c)

		return;

	/* Grab 2nd dword of counter and increment */

	c = GETU32(counter +  4);

	c++;	c &= 0xFFFFFFFF;

	PUTU32(counter +  4, c);

	/* if no overflow, we're done */

	if (c)

		return;

	/* Grab top dword of counter and increment */

	c = GETU32(counter +  0);

	c++;	c &= 0xFFFFFFFF;

	PUTU32(counter +  0, c);

}

/* The input encrypted as though 128bit counter mode is being

 * used.  The extra state information to record how much of the

 * 128bit block we have used is contained in *num, and the

 * encrypted counter is kept in ecount_buf.  Both *num and

 * ecount_buf must be initialised with zeros before the first

 * call to AES_ctr128_encrypt().

 *

 * This algorithm assumes that the counter is in the x lower bits

 * of the IV (ivec), and that the application has full control over

 * overflow and the rest of the IV.  This implementation takes NO

 * responsability for checking that the counter doesn't overflow

 * into the rest of the IV when incremented.

 */

EXPORT_C void AES_ctr128_encrypt(const unsigned char *in, unsigned char *out,

	const unsigned long length, const AES_KEY *key,

	unsigned char ivec[AES_BLOCK_SIZE],

	unsigned char ecount_buf[AES_BLOCK_SIZE],

	unsigned int *num) {

	unsigned int n;

	unsigned long l=length;

	assert(in && out && key && counter && num);

	assert(*num < AES_BLOCK_SIZE);

	n = *num;

	while (l--) {

		if (n == 0) {

			AES_encrypt(ivec, ecount_buf, key);

 			AES_ctr128_inc(ivec);

		}

		*(out++) = *(in++) ^ ecount_buf[n];

		n = (n+1) % AES_BLOCK_SIZE;

	}

	*num=n;

}