n-fold.c

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/*
 * Copyright (c) 1999 Kungliga Tekniska H鰃skolan
 * (Royal Institute of Technology, Stockholm, Sweden). 
 * All rights reserved. 
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met: 
 *
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in the 
 *    documentation and/or other materials provided with the distribution. 
 *
 * 3. Neither the name of KTH nor the names of its contributors may be
 *    used to endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY KTH AND ITS CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KTH OR ITS CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */

#include "krb5_locl.h"

RCSID("$Id: n-fold.c 22190 2007-12-06 16:24:22Z lha $");

static krb5_error_code
rr13(unsigned char *buf, size_t len)
{
    unsigned char *tmp;
    int bytes = (len + 7) / 8;
    int i;
    if(len == 0)
	return 0;
    {
	const int bits = 13 % len;
	const int lbit = len % 8;
    
	tmp = malloc(bytes);
	if (tmp == NULL)
	    return ENOMEM;
	memcpy(tmp, buf, bytes);
	if(lbit) {
	    /* pad final byte with inital bits */
	    tmp[bytes - 1] &= 0xff << (8 - lbit);
	    for(i = lbit; i < 8; i += len)
		tmp[bytes - 1] |= buf[0] >> i;
	}
	for(i = 0; i < bytes; i++) {
	    int bb;
	    int b1, s1, b2, s2;
	    /* calculate first bit position of this byte */
	    bb = 8 * i - bits;
	    while(bb < 0)
		bb += len;
	    /* byte offset and shift count */
	    b1 = bb / 8;
	    s1 = bb % 8;
	
	    if(bb + 8 > bytes * 8) 
		/* watch for wraparound */
		s2 = (len + 8 - s1) % 8;
	    else 
		s2 = 8 - s1;
	    b2 = (b1 + 1) % bytes;
	    buf[i] = (tmp[b1] << s1) | (tmp[b2] >> s2);
	}
	free(tmp);
    }
    return 0;
}

/* Add `b' to `a', both being one's complement numbers. */
static void
add1(unsigned char *a, unsigned char *b, size_t len)
{
    int i;
    int carry = 0;
    for(i = len - 1; i >= 0; i--){
	int x = a[i] + b[i] + carry;
	carry = x > 0xff;
	a[i] = x & 0xff;
    }
    for(i = len - 1; carry && i >= 0; i--){
	int x = a[i] + carry;
	carry = x > 0xff;
	a[i] = x & 0xff;
    }
}

krb5_error_code KRB5_LIB_FUNCTION
_krb5_n_fold(const void *str, size_t len, void *key, size_t size)
{
    /* if len < size we need at most N * len bytes, ie < 2 * size;
       if len > size we need at most 2 * len */
    krb5_error_code ret = 0;
    size_t maxlen = 2 * max(size, len);
    size_t l = 0;
    unsigned char *tmp = malloc(maxlen);
    unsigned char *buf = malloc(len);
    
    if (tmp == NULL || buf == NULL) 
	return ENOMEM;

    memcpy(buf, str, len);
    memset(key, 0, size);
    do {
	memcpy(tmp + l, buf, len);
	l += len;
	ret = rr13(buf, len * 8);
	if (ret)
	    goto out;
	while(l >= size) {
	    add1(key, tmp, size);
	    l -= size;
	    if(l == 0)
		break;
	    memmove(tmp, tmp + size, l);
	}
    } while(l != 0);
out:
    memset(buf, 0, len);
    free(buf);
    memset(tmp, 0, maxlen);
    free(tmp);
    return ret;
}