Applied OpenSSL: CTR Mode in File Encryption

/* ====================================================================
 * Copyright (c) 2008 The OpenSSL Project.  All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
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 *    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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#include "openssl\modes.h"
#include <string.h>

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

#define STRICT_ALIGNMENT
#if defined(__i386) || defined(__i386__) || \
    defined(__x86_64) || defined(__x86_64__) || \
    defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64) || \
    defined(__s390__) || defined(__s390x__)
#  undef STRICT_ALIGNMENT
#endif

/* The input and output encrypted as though 128bit cfb mode is being
 * used.  The extra state information to record how much of the
 * 128bit block we have used is contained in *num;
 */
void CRYPTO_cfb128_encrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], int *num,
			int enc, block128_f block)
{
    unsigned int n;
    size_t l = 0;

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

    n = *num;

    if (enc) {
#if !defined(OPENSSL_SMALL_FOOTPRINT)
	if (16%sizeof(size_t) == 0) do {	/* always true actually */
		while (n && len) {
			*(out++) = ivec[n] ^= *(in++);
			--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, ivec, key);
			for (; n<16; n+=sizeof(size_t)) {
				*(size_t*)(out+n) =
				*(size_t*)(ivec+n) ^= *(size_t*)(in+n);
			}
			len -= 16;
			out += 16;
			in  += 16;
			n = 0;
		}
		if (len) {
			(*block)(ivec, ivec, key);
			while (len--) {
				out[n] = ivec[n] ^= in[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, ivec, key);
		}
		out[l] = ivec[n] ^= in[l];
		++l;
		n = (n+1) % 16;
	}
	*num = n;
    } else {
#if !defined(OPENSSL_SMALL_FOOTPRINT)
	if (16%sizeof(size_t) == 0) do {	/* always true actually */
		while (n && len) {
			unsigned char c;
			*(out++) = ivec[n] ^ (c = *(in++)); ivec[n] = c;
			--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, ivec, key);
			for (; n<16; n+=sizeof(size_t)) {
				size_t t = *(size_t*)(in+n);
				*(size_t*)(out+n) = *(size_t*)(ivec+n) ^ t;
				*(size_t*)(ivec+n) = t;
			}
			len -= 16;
			out += 16;
			in  += 16;
			n = 0;
		}
		if (len) {
			(*block)(ivec, ivec, key);
			while (len--) {
				unsigned char c;
				out[n] = ivec[n] ^ (c = in[n]); ivec[n] = c;
				++n;
			}
 		}
		*num = n;
		return;
	} while (0);
	/* the rest would be commonly eliminated by x86* compiler */
#endif
	while (l<len) {
		unsigned char c;
		if (n == 0) {
			(*block)(ivec, ivec, key);
		}
		out[l] = ivec[n] ^ (c = in[l]); ivec[n] = c;
		++l;
		n = (n+1) % 16;
	}
	*num=n;
    }
}

/* This expects a single block of size nbits for both in and out. Note that
   it corrupts any extra bits in the last byte of out */
static void cfbr_encrypt_block(const unsigned char *in,unsigned char *out,
			    int nbits,const void *key,
			    unsigned char ivec[16],int enc,
			    block128_f block)
{
    int n,rem,num;
    unsigned char ovec[16*2 + 1];  /* +1 because we dererefence (but don't use) one byte off the end */

    if (nbits<=0 || nbits>128) return;

	/* fill in the first half of the new IV with the current IV */
	memcpy(ovec,ivec,16);
	/* construct the new IV */
	(*block)(ivec,ivec,key);
	num = (nbits+7)/8;
	if (enc)	/* encrypt the input */
	    for(n=0 ; n < num ; ++n)
		out[n] = (ovec[16+n] = in[n] ^ ivec[n]);
	else		/* decrypt the input */
	    for(n=0 ; n < num ; ++n)
		out[n] = (ovec[16+n] = in[n]) ^ ivec[n];
	/* shift ovec left... */
	rem = nbits%8;
	num = nbits/8;
	if(rem==0)
	    memcpy(ivec,ovec+num,16);
	else
	    for(n=0 ; n < 16 ; ++n)
		ivec[n] = ovec[n+num]<<rem | ovec[n+num+1]>>(8-rem);

    /* it is not necessary to cleanse ovec, since the IV is not secret */
}

/* N.B. This expects the input to be packed, MS bit first */
void CRYPTO_cfb128_1_encrypt(const unsigned char *in, unsigned char *out,
		 	size_t bits, const void *key,
			unsigned char ivec[16], int *num,
			int enc, block128_f block)
{
    size_t n;
    unsigned char c[1],d[1];

    assert(in && out && key && ivec && num);
    assert(*num == 0);

    for(n=0 ; n<bits ; ++n)
	{
	c[0]=(in[n/8]&(1 << (7-n%8))) ? 0x80 : 0;
	cfbr_encrypt_block(c,d,1,key,ivec,enc,block);
	out[n/8]=(out[n/8]&~(1 << (unsigned int)(7-n%8))) |
		 ((d[0]&0x80) >> (unsigned int)(n%8));
	}
}

void CRYPTO_cfb128_8_encrypt(const unsigned char *in, unsigned char *out,
			size_t length, const void *key,
			unsigned char ivec[16], int *num,
			int enc, block128_f block)
{
    size_t n;

    assert(in && out && key && ivec && num);
    assert(*num == 0);

    for(n=0 ; n<length ; ++n)
	cfbr_encrypt_block(&in[n],&out[n],8,key,ivec,enc,block);
}