xref: /openssl/crypto/bn/bn_mpi.c (revision 9311d0c4)
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 
BN_bn2mpi(const BIGNUM * a,unsigned char * d)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 
BN_mpi2bn(const unsigned char * d,int n,BIGNUM * ain)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