ctr128.c

/* ====================================================================
 * Copyright (c) 2008 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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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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 * 5. Products derived from this software may not be called "OpenSSL"
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 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
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#include <openssl/crypto.h>
#include "modes_lcl.h"
#include <string.h>

#ifndef MODES_DEBUG
# ifndef NDEBUG
#  define NDEBUG
# endif
#endif
#include <assert.h>

/* NOTE: the IV/counter CTR mode is big-endian.  The code itself
 * is endian-neutral. */

/* increment counter (128-bit int) by 1 */
static void ctr128_inc(unsigned char *counter) {
	u32 n=16;
	u8  c;

	do {
		--n;
		c = counter[n];
		++c;
		counter[n] = c;
		if (c) return;
	} while (n);
}

#if !defined(OPENSSL_SMALL_FOOTPRINT)
static void ctr128_inc_aligned(unsigned char *counter) {
	size_t *data,c,n;
	const union { long one; char little; } is_endian = {1};

	if (is_endian.little) {
		ctr128_inc(counter);
		return;
	}

	data = (size_t *)counter;
	n = 16/sizeof(size_t);
	do {
		--n;
		c = data[n];
		++c;
		data[n] = c;
		if (c) return;
	} while (n);
}
#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, and the
 * encrypted counter is kept in ecount_buf.  Both *num and
 * ecount_buf must be initialised with zeros before the first
 * call to CRYPTO_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.
 */
void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], unsigned char ecount_buf[16],
			unsigned int *num, block128_f block)
{
	unsigned int n;
	size_t l=0;

	assert(in && out && key && ecount_buf && num);
	assert(*num < 16);

	n = *num;

#if !defined(OPENSSL_SMALL_FOOTPRINT)
	if (16%sizeof(size_t) == 0) do { /* always true actually */
		while (n && len) {
			*(out++) = *(in++) ^ ecount_buf[n];
			--len;
			n = (n+1) % 16;
		}

#if defined(STRICT_ALIGNMENT)
		if (((size_t)in|(size_t)out|(size_t)ivec)%sizeof(size_t) != 0)
			break;
#endif
		while (len>=16) {
			(*block)(ivec, ecount_buf, key);
			ctr128_inc_aligned(ivec);
			for (; n<16; n+=sizeof(size_t))
				*(size_t *)(out+n) =
				*(size_t *)(in+n) ^ *(size_t *)(ecount_buf+n);
			len -= 16;
			out += 16;
			in  += 16;
			n = 0;
		}
		if (len) {
			(*block)(ivec, ecount_buf, key);
 			ctr128_inc_aligned(ivec);
			while (len--) {
				out[n] = in[n] ^ ecount_buf[n];
				++n;
			}
		}
		*num = n;
		return;
	} while(0);
	/* the rest would be commonly eliminated by x86* compiler */
#endif
	while (l<len) {
		if (n==0) {
			(*block)(ivec, ecount_buf, key);
 			ctr128_inc(ivec);
		}
		out[l] = in[l] ^ ecount_buf[n];
		++l;
		n = (n+1) % 16;
	}

	*num=n;
}

/* increment upper 96 bits of 128-bit counter by 1 */
static void ctr96_inc(unsigned char *counter) {
	u32 n=12;
	u8  c;

	do {
		--n;
		c = counter[n];
		++c;
		counter[n] = c;
		if (c) return;
	} while (n);
}

void CRYPTO_ctr128_encrypt_ctr32(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], unsigned char ecount_buf[16],
			unsigned int *num, ctr128_f func)
{
	unsigned int n,ctr32;

	assert(in && out && key && ecount_buf && num);
	assert(*num < 16);

	n = *num;

	while (n && len) {
		*(out++) = *(in++) ^ ecount_buf[n];
		--len;
		n = (n+1) % 16;
	}

	ctr32 = GETU32(ivec+12);
	while (len>=16) {
		size_t blocks = len/16;
		/*
		 * 1<<28 is just a not-so-small yet not-so-large number...
		 * Below condition is practically never met, but it has to
		 * be checked for code correctness.
		 */
		if (sizeof(size_t)>sizeof(unsigned int) && blocks>(1U<<28))
			blocks = (1U<<28);
		/*
		 * As (*func) operates on 32-bit counter, caller
		 * has to handle overflow. 'if' below detects the
		 * overflow, which is then handled by limiting the
		 * amount of blocks to the exact overflow point...
		 */
		ctr32 += (u32)blocks;
		if (ctr32 < blocks) {
			blocks -= ctr32;
			ctr32   = 0;
		}
		(*func)(in,out,blocks,key,ivec);
		/* (*ctr) does not update ivec, caller does: */
		PUTU32(ivec+12,ctr32);
		/* ... overflow was detected, propogate carry. */
		if (ctr32 == 0)	ctr96_inc(ivec);
		blocks *= 16;
		len -= blocks;
		out += blocks;
		in  += blocks;
	}
	if (len) {
		memset(ecount_buf,0,16);
		(*func)(ecount_buf,ecount_buf,1,key,ivec);
		++ctr32;
		PUTU32(ivec+12,ctr32);
		if (ctr32 == 0)	ctr96_inc(ivec);
		while (len--) {
			out[n] = in[n] ^ ecount_buf[n];
			++n;
		}
	}

	*num=n;
}