/*
 * Copyright (c) 1999 Kungliga Tekniska Högskolan
 * (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"

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_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
_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) {
        ret = ENOMEM;
        goto out;
    }

    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:
    if (buf) {
        memset(buf, 0, len);
        free(buf);
    }
    if (tmp) {
        memset(tmp, 0, maxlen);
        free(tmp);
    }
    return ret;
}