1/*
2 * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (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
19typedef 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 */
29static 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
96int 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        CTerr(CT_F_SCT_CTX_VERIFY, CT_R_SCT_NOT_SET);
105        return 0;
106    }
107    if (sct->version != SCT_VERSION_V1) {
108        CTerr(CT_F_SCT_CTX_VERIFY, 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        CTerr(CT_F_SCT_CTX_VERIFY, CT_R_SCT_LOG_ID_MISMATCH);
114        return 0;
115    }
116    if (sct->timestamp > sctx->epoch_time_in_ms) {
117        CTerr(CT_F_SCT_CTX_VERIFY, 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(ctx, NULL, EVP_sha256(), NULL, sctx->pkey))
126        goto end;
127
128    if (!sct_ctx_update(ctx, sctx, sct))
129        goto end;
130
131    /* Verify signature */
132    ret = EVP_DigestVerifyFinal(ctx, sct->sig, sct->sig_len);
133    /* If ret < 0 some other error: fall through without setting error */
134    if (ret == 0)
135        CTerr(CT_F_SCT_CTX_VERIFY, CT_R_SCT_INVALID_SIGNATURE);
136
137end:
138    EVP_MD_CTX_free(ctx);
139    return ret;
140}
141