ofb128.c

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/* ====================================================================
 * 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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 *
 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in
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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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 *    "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>

/* The input and output encrypted as though 128bit ofb 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_ofb128_encrypt(const unsigned char *in, unsigned char *out,
            size_t len, const void *key,
            unsigned char ivec[16], int *num,
            block128_f block)
{
    unsigned int n;
    size_t l=0;

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

    n = *num;

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

    *num=n;
}