xref: /openssl/crypto/ct/ct_vfy.c (revision 3c2bdd7d)
1 /*
2  * Copyright 2016-2021 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 <string.h>
11 
12 #include <openssl/ct.h>
13 #include <openssl/err.h>
14 #include <openssl/evp.h>
15 #include <openssl/x509.h>
16 
17 #include "ct_local.h"
18 
19 typedef enum sct_signature_type_t {
20     SIGNATURE_TYPE_NOT_SET = -1,
21     SIGNATURE_TYPE_CERT_TIMESTAMP,
22     SIGNATURE_TYPE_TREE_HASH
23 } SCT_SIGNATURE_TYPE;
24 
25 /*
26  * Update encoding for SCT signature verification/generation to supplied
27  * EVP_MD_CTX.
28  */
sct_ctx_update(EVP_MD_CTX * ctx,const SCT_CTX * sctx,const SCT * sct)29 static int sct_ctx_update(EVP_MD_CTX *ctx, const SCT_CTX *sctx, const SCT *sct)
30 {
31     unsigned char tmpbuf[12];
32     unsigned char *p, *der;
33     size_t derlen;
34     /*+
35      * digitally-signed struct {
36      *   (1 byte) Version sct_version;
37      *   (1 byte) SignatureType signature_type = certificate_timestamp;
38      *   (8 bytes) uint64 timestamp;
39      *   (2 bytes) LogEntryType entry_type;
40      *   (? bytes) select(entry_type) {
41      *     case x509_entry: ASN.1Cert;
42      *     case precert_entry: PreCert;
43      *   } signed_entry;
44      *   (2 bytes + sct->ext_len) CtExtensions extensions;
45      * }
46      */
47     if (sct->entry_type == CT_LOG_ENTRY_TYPE_NOT_SET)
48         return 0;
49     if (sct->entry_type == CT_LOG_ENTRY_TYPE_PRECERT && sctx->ihash == NULL)
50         return 0;
51 
52     p = tmpbuf;
53     *p++ = sct->version;
54     *p++ = SIGNATURE_TYPE_CERT_TIMESTAMP;
55     l2n8(sct->timestamp, p);
56     s2n(sct->entry_type, p);
57 
58     if (!EVP_DigestUpdate(ctx, tmpbuf, p - tmpbuf))
59         return 0;
60 
61     if (sct->entry_type == CT_LOG_ENTRY_TYPE_X509) {
62         der = sctx->certder;
63         derlen = sctx->certderlen;
64     } else {
65         if (!EVP_DigestUpdate(ctx, sctx->ihash, sctx->ihashlen))
66             return 0;
67         der = sctx->preder;
68         derlen = sctx->prederlen;
69     }
70 
71     /* If no encoding available, fatal error */
72     if (der == NULL)
73         return 0;
74 
75     /* Include length first */
76     p = tmpbuf;
77     l2n3(derlen, p);
78 
79     if (!EVP_DigestUpdate(ctx, tmpbuf, 3))
80         return 0;
81     if (!EVP_DigestUpdate(ctx, der, derlen))
82         return 0;
83 
84     /* Add any extensions */
85     p = tmpbuf;
86     s2n(sct->ext_len, p);
87     if (!EVP_DigestUpdate(ctx, tmpbuf, 2))
88         return 0;
89 
90     if (sct->ext_len && !EVP_DigestUpdate(ctx, sct->ext, sct->ext_len))
91         return 0;
92 
93     return 1;
94 }
95 
SCT_CTX_verify(const SCT_CTX * sctx,const SCT * sct)96 int SCT_CTX_verify(const SCT_CTX *sctx, const SCT *sct)
97 {
98     EVP_MD_CTX *ctx = NULL;
99     int ret = 0;
100 
101     if (!SCT_is_complete(sct) || sctx->pkey == NULL ||
102         sct->entry_type == CT_LOG_ENTRY_TYPE_NOT_SET ||
103         (sct->entry_type == CT_LOG_ENTRY_TYPE_PRECERT && sctx->ihash == NULL)) {
104         ERR_raise(ERR_LIB_CT, CT_R_SCT_NOT_SET);
105         return 0;
106     }
107     if (sct->version != SCT_VERSION_V1) {
108         ERR_raise(ERR_LIB_CT, CT_R_SCT_UNSUPPORTED_VERSION);
109         return 0;
110     }
111     if (sct->log_id_len != sctx->pkeyhashlen ||
112         memcmp(sct->log_id, sctx->pkeyhash, sctx->pkeyhashlen) != 0) {
113         ERR_raise(ERR_LIB_CT, CT_R_SCT_LOG_ID_MISMATCH);
114         return 0;
115     }
116     if (sct->timestamp > sctx->epoch_time_in_ms) {
117         ERR_raise(ERR_LIB_CT, CT_R_SCT_FUTURE_TIMESTAMP);
118         return 0;
119     }
120 
121     ctx = EVP_MD_CTX_new();
122     if (ctx == NULL)
123         goto end;
124 
125     if (!EVP_DigestVerifyInit_ex(ctx, NULL, "SHA2-256", sctx->libctx,
126                                  sctx->propq, sctx->pkey, NULL))
127         goto end;
128 
129     if (!sct_ctx_update(ctx, sctx, sct))
130         goto end;
131 
132     /* Verify signature */
133     ret = EVP_DigestVerifyFinal(ctx, sct->sig, sct->sig_len);
134     /* If ret < 0 some other error: fall through without setting error */
135     if (ret == 0)
136         ERR_raise(ERR_LIB_CT, CT_R_SCT_INVALID_SIGNATURE);
137 
138 end:
139     EVP_MD_CTX_free(ctx);
140     return ret;
141 }
142