crypto/ct/ct_vfy.c

   1 /*
   2  * Copyright 2016 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 ||
 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
 137 end:
 138     EVP_MD_CTX_free(ctx);
 139     return ret;
 140 }