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      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  */
     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 
     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 || sct->entry_type == CT_LOG_ENTRY_TYPE_NOT_SET || (sct->entry_type == CT_LOG_ENTRY_TYPE_PRECERT && sctx->ihash == NULL)) {
    102         ERR_raise(ERR_LIB_CT, CT_R_SCT_NOT_SET);
    103         return 0;
    104     }
    105     if (sct->version != SCT_VERSION_V1) {
    106         ERR_raise(ERR_LIB_CT, CT_R_SCT_UNSUPPORTED_VERSION);
    107         return 0;
    108     }
    109     if (sct->log_id_len != sctx->pkeyhashlen || memcmp(sct->log_id, sctx->pkeyhash, sctx->pkeyhashlen) != 0) {
    110         ERR_raise(ERR_LIB_CT, CT_R_SCT_LOG_ID_MISMATCH);
    111         return 0;
    112     }
    113     if (sct->timestamp > sctx->epoch_time_in_ms) {
    114         ERR_raise(ERR_LIB_CT, CT_R_SCT_FUTURE_TIMESTAMP);
    115         return 0;
    116     }
    117 
    118     ctx = EVP_MD_CTX_new();
    119     if (ctx == NULL)
    120         goto end;
    121 
    122     if (!EVP_DigestVerifyInit_ex(ctx, NULL, "SHA2-256", sctx->libctx,
    123             sctx->propq, sctx->pkey, NULL))
    124         goto end;
    125 
    126     if (!sct_ctx_update(ctx, sctx, sct))
    127         goto end;
    128 
    129     /* Verify signature */
    130     ret = EVP_DigestVerifyFinal(ctx, sct->sig, sct->sig_len);
    131     /* If ret < 0 some other error: fall through without setting error */
    132     if (ret == 0)
    133         ERR_raise(ERR_LIB_CT, CT_R_SCT_INVALID_SIGNATURE);
    134 
    135 end:
    136     EVP_MD_CTX_free(ctx);
    137     return ret;
    138 }
    139