crypto/bn/bn_mpi.c

   1 /*
   2  * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include <stdio.h>
  11 #include "internal/cryptlib.h"
  12 #include "bn_local.h"
  13
  14 int BN_bn2mpi(const BIGNUM *a, unsigned char *d)
  15 {
  16     int bits;
  17     int num = 0;
  18     int ext = 0;
  19     long l;
  20
  21     bits = BN_num_bits(a);
  22     num = (bits + 7) / 8;
  23     if (bits > 0) {
  24         ext = ((bits & 0x07) == 0);
  25     }
  26     if (d == NULL)
  27         return (num + 4 + ext);
  28
  29     l = num + ext;
  30     d[0] = (unsigned char)(l >> 24) & 0xff;
  31     d[1] = (unsigned char)(l >> 16) & 0xff;
  32     d[2] = (unsigned char)(l >> 8) & 0xff;
  33     d[3] = (unsigned char)(l) & 0xff;
  34     if (ext)
  35         d[4] = 0;
  36     num = BN_bn2bin(a, &(d[4 + ext]));
  37     if (a->neg)
  38         d[4] |= 0x80;
  39     return (num + 4 + ext);
  40 }
  41
  42 BIGNUM *BN_mpi2bn(const unsigned char *d, int n, BIGNUM *ain)
  43 {
  44     long len;
  45     int neg = 0;
  46     BIGNUM *a = NULL;
  47
  48     if (n < 4 || (d[0] & 0x80) != 0) {
  49         BNerr(BN_F_BN_MPI2BN, BN_R_INVALID_LENGTH);
  50         return NULL;
  51     }
  52     len = ((long)d[0] << 24) | ((long)d[1] << 16) | ((int)d[2] << 8) | (int)
  53         d[3];
  54     if ((len + 4) != n) {
  55         BNerr(BN_F_BN_MPI2BN, BN_R_ENCODING_ERROR);
  56         return NULL;
  57     }
  58
  59     if (ain == NULL)
  60         a = BN_new();
  61     else
  62         a = ain;
  63
  64     if (a == NULL)
  65         return NULL;
  66
  67     if (len == 0) {
  68         a->neg = 0;
  69         a->top = 0;
  70         return a;
  71     }
  72     d += 4;
  73     if ((*d) & 0x80)
  74         neg = 1;
  75     if (BN_bin2bn(d, (int)len, a) == NULL) {
  76         if (ain == NULL)
  77             BN_free(a);
  78         return NULL;
  79     }
  80     a->neg = neg;
  81     if (neg) {
  82         BN_clear_bit(a, BN_num_bits(a) - 1);
  83     }
  84     bn_check_top(a);
  85     return a;
  86 }