xref: /openssl/crypto/der_writer.c (revision 59196250)
1 /*
2  * Copyright 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 <stdlib.h>
11 #include <string.h>
12 #include "internal/cryptlib.h"
13 #include "internal/der.h"
14 #include "crypto/bn.h"
15 
int_start_context(WPACKET * pkt,int tag)16 static int int_start_context(WPACKET *pkt, int tag)
17 {
18     if (tag < 0)
19         return 1;
20     if (!ossl_assert(tag <= 30))
21         return 0;
22     return WPACKET_start_sub_packet(pkt);
23 }
24 
int_end_context(WPACKET * pkt,int tag)25 static int int_end_context(WPACKET *pkt, int tag)
26 {
27     /*
28      * If someone set the flag WPACKET_FLAGS_ABANDON_ON_ZERO_LENGTH on this
29      * sub-packet and this sub-packet has nothing written to it, the DER length
30      * will not be written, and the total written size will be unchanged before
31      * and after WPACKET_close().  We use size1 and size2 to determine if
32      * anything was written, and only write our tag if it has.
33      *
34      */
35     size_t size1, size2;
36 
37     if (tag < 0)
38         return 1;
39     if (!ossl_assert(tag <= 30))
40         return 0;
41 
42     /* Context specific are normally (?) constructed */
43     tag |= DER_F_CONSTRUCTED | DER_C_CONTEXT;
44 
45     return WPACKET_get_total_written(pkt, &size1)
46         && WPACKET_close(pkt)
47         && WPACKET_get_total_written(pkt, &size2)
48         && (size1 == size2 || WPACKET_put_bytes_u8(pkt, tag));
49 }
50 
ossl_DER_w_precompiled(WPACKET * pkt,int tag,const unsigned char * precompiled,size_t precompiled_n)51 int ossl_DER_w_precompiled(WPACKET *pkt, int tag,
52                            const unsigned char *precompiled,
53                            size_t precompiled_n)
54 {
55     return int_start_context(pkt, tag)
56         && WPACKET_memcpy(pkt, precompiled, precompiled_n)
57         && int_end_context(pkt, tag);
58 }
59 
ossl_DER_w_boolean(WPACKET * pkt,int tag,int b)60 int ossl_DER_w_boolean(WPACKET *pkt, int tag, int b)
61 {
62     return int_start_context(pkt, tag)
63         && WPACKET_start_sub_packet(pkt)
64         && (!b || WPACKET_put_bytes_u8(pkt, 0xFF))
65         && !WPACKET_close(pkt)
66         && !WPACKET_put_bytes_u8(pkt, DER_P_BOOLEAN)
67         && int_end_context(pkt, tag);
68 }
69 
ossl_DER_w_octet_string(WPACKET * pkt,int tag,const unsigned char * data,size_t data_n)70 int ossl_DER_w_octet_string(WPACKET *pkt, int tag,
71                             const unsigned char *data, size_t data_n)
72 {
73     return int_start_context(pkt, tag)
74         && WPACKET_start_sub_packet(pkt)
75         && WPACKET_memcpy(pkt, data, data_n)
76         && WPACKET_close(pkt)
77         && WPACKET_put_bytes_u8(pkt, DER_P_OCTET_STRING)
78         && int_end_context(pkt, tag);
79 }
80 
ossl_DER_w_octet_string_uint32(WPACKET * pkt,int tag,uint32_t value)81 int ossl_DER_w_octet_string_uint32(WPACKET *pkt, int tag, uint32_t value)
82 {
83     unsigned char tmp[4] = { 0, 0, 0, 0 };
84     unsigned char *pbuf = tmp + (sizeof(tmp) - 1);
85 
86     while (value > 0) {
87         *pbuf-- = (value & 0xFF);
88         value >>= 8;
89     }
90     return ossl_DER_w_octet_string(pkt, tag, tmp, sizeof(tmp));
91 }
92 
int_der_w_integer(WPACKET * pkt,int tag,int (* put_bytes)(WPACKET * pkt,const void * v,unsigned int * top_byte),const void * v)93 static int int_der_w_integer(WPACKET *pkt, int tag,
94                              int (*put_bytes)(WPACKET *pkt, const void *v,
95                                               unsigned int *top_byte),
96                              const void *v)
97 {
98     unsigned int top_byte = 0;
99 
100     return int_start_context(pkt, tag)
101         && WPACKET_start_sub_packet(pkt)
102         && put_bytes(pkt, v, &top_byte)
103         && ((top_byte & 0x80) == 0 || WPACKET_put_bytes_u8(pkt, 0))
104         && WPACKET_close(pkt)
105         && WPACKET_put_bytes_u8(pkt, DER_P_INTEGER)
106         && int_end_context(pkt, tag);
107 }
108 
int_put_bytes_uint32(WPACKET * pkt,const void * v,unsigned int * top_byte)109 static int int_put_bytes_uint32(WPACKET *pkt, const void *v,
110                                unsigned int *top_byte)
111 {
112     const uint32_t *value = v;
113     uint32_t tmp = *value;
114     size_t n = 0;
115 
116     while (tmp != 0) {
117         n++;
118         *top_byte = (tmp & 0xFF);
119         tmp >>= 8;
120     }
121     if (n == 0)
122         n = 1;
123 
124     return WPACKET_put_bytes__(pkt, *value, n);
125 }
126 
127 /* For integers, we only support unsigned values for now */
ossl_DER_w_uint32(WPACKET * pkt,int tag,uint32_t v)128 int ossl_DER_w_uint32(WPACKET *pkt, int tag, uint32_t v)
129 {
130     return int_der_w_integer(pkt, tag, int_put_bytes_uint32, &v);
131 }
132 
int_put_bytes_bn(WPACKET * pkt,const void * v,unsigned int * top_byte)133 static int int_put_bytes_bn(WPACKET *pkt, const void *v,
134                             unsigned int *top_byte)
135 {
136     unsigned char *p = NULL;
137     size_t n = BN_num_bytes(v);
138 
139     /* The BIGNUM limbs are in LE order */
140     *top_byte =
141         ((bn_get_words(v) [(n - 1) / BN_BYTES]) >> (8 * ((n - 1) % BN_BYTES)))
142         & 0xFF;
143 
144     if (!WPACKET_allocate_bytes(pkt, n, &p))
145         return 0;
146     if (p != NULL)
147         BN_bn2bin(v, p);
148     return 1;
149 }
150 
ossl_DER_w_bn(WPACKET * pkt,int tag,const BIGNUM * v)151 int ossl_DER_w_bn(WPACKET *pkt, int tag, const BIGNUM *v)
152 {
153     if (v == NULL || BN_is_negative(v))
154         return 0;
155     if (BN_is_zero(v))
156         return ossl_DER_w_uint32(pkt, tag, 0);
157 
158     return int_der_w_integer(pkt, tag, int_put_bytes_bn, v);
159 }
160 
ossl_DER_w_null(WPACKET * pkt,int tag)161 int ossl_DER_w_null(WPACKET *pkt, int tag)
162 {
163     return int_start_context(pkt, tag)
164         && WPACKET_start_sub_packet(pkt)
165         && WPACKET_close(pkt)
166         && WPACKET_put_bytes_u8(pkt, DER_P_NULL)
167         && int_end_context(pkt, tag);
168 }
169 
170 /* Constructed things need a start and an end */
ossl_DER_w_begin_sequence(WPACKET * pkt,int tag)171 int ossl_DER_w_begin_sequence(WPACKET *pkt, int tag)
172 {
173     return int_start_context(pkt, tag)
174         && WPACKET_start_sub_packet(pkt);
175 }
176 
ossl_DER_w_end_sequence(WPACKET * pkt,int tag)177 int ossl_DER_w_end_sequence(WPACKET *pkt, int tag)
178 {
179     /*
180      * If someone set the flag WPACKET_FLAGS_ABANDON_ON_ZERO_LENGTH on this
181      * sub-packet and this sub-packet has nothing written to it, the DER length
182      * will not be written, and the total written size will be unchanged before
183      * and after WPACKET_close().  We use size1 and size2 to determine if
184      * anything was written, and only write our tag if it has.
185      *
186      * Because we know that int_end_context() needs to do the same check,
187      * we reproduce this flag if the written length was unchanged, or we will
188      * have an erroneous context tag.
189      */
190     size_t size1, size2;
191 
192     return WPACKET_get_total_written(pkt, &size1)
193         && WPACKET_close(pkt)
194         && WPACKET_get_total_written(pkt, &size2)
195         && (size1 == size2
196             ? WPACKET_set_flags(pkt, WPACKET_FLAGS_ABANDON_ON_ZERO_LENGTH)
197             : WPACKET_put_bytes_u8(pkt, DER_F_CONSTRUCTED | DER_P_SEQUENCE))
198         && int_end_context(pkt, tag);
199 }
200