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      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         ERR_raise(ERR_LIB_BN, 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         ERR_raise(ERR_LIB_BN, 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 }
     87