openssl/crypto/aes/aes_ctr.c

/* crypto/aes/aes_ctr.c -*- mode:C; c-file-style: "eay" -*- */
/* ====================================================================
 * Copyright (c) 1998-2002 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
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 *    notice, this list of conditions and the following disclaimer. 
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 *    distribution.
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 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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 *    openssl-core@openssl.org.
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 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
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 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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 */

#include <assert.h>
#include <openssl/aes.h>
#include "aes_locl.h"

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

/* increment counter (128-bit int) by 2^64 */
static void AES_ctr128_inc(unsigned char *counter) {
	unsigned long c;

	/* Grab 3rd dword of counter and increment */
#ifdef L_ENDIAN
	c = GETU32(counter + 8);
	c++;
	PUTU32(counter + 8, c);
#else
	c = GETU32(counter + 4);
	c++;
	PUTU32(counter + 4, c);
#endif

	/* if no overflow, we're done */
	if (c)
		return;

	/* Grab top dword of counter and increment */
#ifdef L_ENDIAN
	c = GETU32(counter + 12);
	c++;
	PUTU32(counter + 12, c);
#else
	c = GETU32(counter +  0);
	c++;
	PUTU32(counter +  0, c);
#endif

}

/* 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;
 */
void AES_ctr128_encrypt(const unsigned char *in, unsigned char *out,
	const unsigned long length, const AES_KEY *key,
	unsigned char *counter, unsigned int *num) {

	unsigned int n;
	unsigned long l=length;
	unsigned char tmp[AES_BLOCK_SIZE];

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

	n = *num;

	while (l--) {
		if (n == 0) {
			AES_encrypt(counter, tmp, key);
			AES_ctr128_inc(counter);
		}
		*(out++) = *(in++) ^ tmp[n];
		n = (n+1) % AES_BLOCK_SIZE;
	}

	*num=n;
}