net/cert/asn1_util.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/cert/asn1_util.h"
   6
   7 namespace net {
   8
   9 namespace asn1 {
  10
  11 bool ParseElement(base::StringPiece* in,
  12                   unsigned tag_value,
  13                   base::StringPiece* out,
  14                   unsigned *out_header_len) {
  15   const uint8_t* data = reinterpret_cast<const uint8_t*>(in->data());
  16
  17   // We don't support kAny and kOptional at the same time.
  18   if ((tag_value & kAny) && (tag_value & kOptional))
  19     return false;
  20
  21   if (in->empty() && (tag_value & kOptional)) {
  22     if (out_header_len)
  23       *out_header_len = 0;
  24     if (out)
  25       *out = base::StringPiece();
  26     return true;
  27   }
  28
  29   if (in->size() < 2)
  30     return false;
  31
  32   if (tag_value != kAny &&
  33       static_cast<unsigned char>(data[0]) != (tag_value & 0xff)) {
  34     if (tag_value & kOptional) {
  35       if (out_header_len)
  36         *out_header_len = 0;
  37       if (out)
  38         *out = base::StringPiece();
  39       return true;
  40     }
  41     return false;
  42   }
  43
  44   size_t len = 0;
  45   if ((data[1] & 0x80) == 0) {
  46     // short form length
  47     if (out_header_len)
  48       *out_header_len = 2;
  49     len = static_cast<size_t>(data[1]) + 2;
  50   } else {
  51     // long form length
  52     const unsigned num_bytes = data[1] & 0x7f;
  53     if (num_bytes == 0 || num_bytes > 2)
  54       return false;
  55     if (in->size() < 2 + num_bytes)
  56       return false;
  57     len = data[2];
  58     if (num_bytes == 2) {
  59       if (len == 0) {
  60         // the length encoding must be minimal.
  61         return false;
  62       }
  63       len <<= 8;
  64       len += data[3];
  65     }
  66     if (len < 128) {
  67       // the length should have been encoded in short form. This distinguishes
  68       // DER from BER encoding.
  69       return false;
  70     }
  71     if (out_header_len)
  72       *out_header_len = 2 + num_bytes;
  73     len += 2 + num_bytes;
  74   }
  75
  76   if (in->size() < len)
  77     return false;
  78   if (out)
  79     *out = base::StringPiece(in->data(), len);
  80   in->remove_prefix(len);
  81   return true;
  82 }
  83
  84 bool GetElement(base::StringPiece* in,
  85                 unsigned tag_value,
  86                 base::StringPiece* out) {
  87   unsigned header_len;
  88   if (!ParseElement(in, tag_value, out, &header_len))
  89     return false;
  90   if (out)
  91     out->remove_prefix(header_len);
  92   return true;
  93 }
  94
  95 // SeekToSPKI changes |cert| so that it points to a suffix of the
  96 // TBSCertificate where the suffix begins at the start of the ASN.1
  97 // SubjectPublicKeyInfo value.
  98 static bool SeekToSPKI(base::StringPiece* cert) {
  99   // From RFC 5280, section 4.1
 100   //    Certificate  ::=  SEQUENCE  {
 101   //      tbsCertificate       TBSCertificate,
 102   //      signatureAlgorithm   AlgorithmIdentifier,
 103   //      signatureValue       BIT STRING  }
 104
 105   // TBSCertificate  ::=  SEQUENCE  {
 106   //      version         [0]  EXPLICIT Version DEFAULT v1,
 107   //      serialNumber         CertificateSerialNumber,
 108   //      signature            AlgorithmIdentifier,
 109   //      issuer               Name,
 110   //      validity             Validity,
 111   //      subject              Name,
 112   //      subjectPublicKeyInfo SubjectPublicKeyInfo,
 113
 114   base::StringPiece certificate;
 115   if (!GetElement(cert, kSEQUENCE, &certificate))
 116     return false;
 117
 118   // We don't allow junk after the certificate.
 119   if (!cert->empty())
 120     return false;
 121
 122   base::StringPiece tbs_certificate;
 123   if (!GetElement(&certificate, kSEQUENCE, &tbs_certificate))
 124     return false;
 125
 126   if (!GetElement(&tbs_certificate,
 127                   kOptional | kConstructed | kContextSpecific | 0,
 128                   NULL)) {
 129     return false;
 130   }
 131
 132   // serialNumber
 133   if (!GetElement(&tbs_certificate, kINTEGER, NULL))
 134     return false;
 135   // signature
 136   if (!GetElement(&tbs_certificate, kSEQUENCE, NULL))
 137     return false;
 138   // issuer
 139   if (!GetElement(&tbs_certificate, kSEQUENCE, NULL))
 140     return false;
 141   // validity
 142   if (!GetElement(&tbs_certificate, kSEQUENCE, NULL))
 143     return false;
 144   // subject
 145   if (!GetElement(&tbs_certificate, kSEQUENCE, NULL))
 146     return false;
 147   *cert = tbs_certificate;
 148   return true;
 149 }
 150
 151 bool ExtractSPKIFromDERCert(base::StringPiece cert,
 152                             base::StringPiece* spki_out) {
 153   if (!SeekToSPKI(&cert))
 154     return false;
 155   if (!ParseElement(&cert, kSEQUENCE, spki_out, NULL))
 156     return false;
 157   return true;
 158 }
 159
 160 bool ExtractSubjectPublicKeyFromSPKI(base::StringPiece spki,
 161                                      base::StringPiece* spk_out) {
 162   // From RFC 5280, Section 4.1
 163   //   SubjectPublicKeyInfo  ::=  SEQUENCE  {
 164   //     algorithm            AlgorithmIdentifier,
 165   //     subjectPublicKey     BIT STRING  }
 166   //
 167   //   AlgorithmIdentifier  ::=  SEQUENCE  {
 168   //     algorithm               OBJECT IDENTIFIER,
 169   //     parameters              ANY DEFINED BY algorithm OPTIONAL  }
 170
 171   // Step into SubjectPublicKeyInfo sequence.
 172   base::StringPiece spki_contents;
 173   if (!asn1::GetElement(&spki, asn1::kSEQUENCE, &spki_contents))
 174     return false;
 175
 176   // Step over algorithm field (a SEQUENCE).
 177   base::StringPiece algorithm;
 178   if (!asn1::GetElement(&spki_contents, asn1::kSEQUENCE, &algorithm))
 179     return false;
 180
 181   // Extract the subjectPublicKey field.
 182   if (!asn1::GetElement(&spki_contents, asn1::kBITSTRING, spk_out))
 183     return false;
 184   return true;
 185 }
 186
 187
 188 bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
 189                                std::vector<base::StringPiece>* urls_out) {
 190   urls_out->clear();
 191   std::vector<base::StringPiece> tmp_urls_out;
 192
 193   if (!SeekToSPKI(&cert))
 194     return false;
 195
 196   // From RFC 5280, section 4.1
 197   // TBSCertificate  ::=  SEQUENCE  {
 198   //      ...
 199   //      subjectPublicKeyInfo SubjectPublicKeyInfo,
 200   //      issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
 201   //      subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
 202   //      extensions      [3]  EXPLICIT Extensions OPTIONAL
 203
 204   // subjectPublicKeyInfo
 205   if (!GetElement(&cert, kSEQUENCE, NULL))
 206     return false;
 207   // issuerUniqueID
 208   if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 1, NULL))
 209     return false;
 210   // subjectUniqueID
 211   if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 2, NULL))
 212     return false;
 213
 214   base::StringPiece extensions_seq;
 215   if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 3,
 216                   &extensions_seq)) {
 217     return false;
 218   }
 219
 220   if (extensions_seq.empty())
 221     return true;
 222
 223   // Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
 224   // Extension   ::=  SEQUENCE  {
 225   //      extnID      OBJECT IDENTIFIER,
 226   //      critical    BOOLEAN DEFAULT FALSE,
 227   //      extnValue   OCTET STRING
 228
 229   // |extensions_seq| was EXPLICITly tagged, so we still need to remove the
 230   // ASN.1 SEQUENCE header.
 231   base::StringPiece extensions;
 232   if (!GetElement(&extensions_seq, kSEQUENCE, &extensions))
 233     return false;
 234
 235   while (extensions.size() > 0) {
 236     base::StringPiece extension;
 237     if (!GetElement(&extensions, kSEQUENCE, &extension))
 238       return false;
 239
 240     base::StringPiece oid;
 241     if (!GetElement(&extension, kOID, &oid))
 242       return false;
 243
 244     // kCRLDistributionPointsOID is the DER encoding of the OID for the X.509
 245     // CRL Distribution Points extension.
 246     static const uint8_t kCRLDistributionPointsOID[] = {0x55, 0x1d, 0x1f};
 247
 248     if (oid.size() != sizeof(kCRLDistributionPointsOID) ||
 249         memcmp(oid.data(), kCRLDistributionPointsOID, oid.size()) != 0) {
 250       continue;
 251     }
 252
 253     // critical
 254     GetElement(&extension, kBOOLEAN, NULL);
 255
 256     // extnValue
 257     base::StringPiece extension_value;
 258     if (!GetElement(&extension, kOCTETSTRING, &extension_value))
 259       return false;
 260
 261     // RFC 5280, section 4.2.1.13.
 262     //
 263     // CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
 264     //
 265     // DistributionPoint ::= SEQUENCE {
 266     //  distributionPoint       [0]     DistributionPointName OPTIONAL,
 267     //  reasons                 [1]     ReasonFlags OPTIONAL,
 268     //  cRLIssuer               [2]     GeneralNames OPTIONAL }
 269
 270     base::StringPiece distribution_points;
 271     if (!GetElement(&extension_value, kSEQUENCE, &distribution_points))
 272       return false;
 273
 274     while (distribution_points.size() > 0) {
 275       base::StringPiece distrib_point;
 276       if (!GetElement(&distribution_points, kSEQUENCE, &distrib_point))
 277         return false;
 278
 279       base::StringPiece name;
 280       if (!GetElement(&distrib_point, kContextSpecific | kConstructed | 0,
 281                       &name)) {
 282         // If it doesn't contain a name then we skip it.
 283         continue;
 284       }
 285
 286       if (GetElement(&distrib_point, kContextSpecific | 1, NULL)) {
 287         // If it contains a subset of reasons then we skip it. We aren't
 288         // interested in subsets of CRLs and the RFC states that there MUST be
 289         // a CRL that covers all reasons.
 290         continue;
 291       }
 292
 293       if (GetElement(&distrib_point,
 294                      kContextSpecific | kConstructed | 2, NULL)) {
 295         // If it contains a alternative issuer, then we skip it.
 296         continue;
 297       }
 298
 299       // DistributionPointName ::= CHOICE {
 300       //   fullName                [0]     GeneralNames,
 301       //   nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
 302       base::StringPiece general_names;
 303       if (!GetElement(&name,
 304                       kContextSpecific | kConstructed | 0, &general_names)) {
 305         continue;
 306       }
 307
 308       // GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
 309       // GeneralName ::= CHOICE {
 310       //   ...
 311       //   uniformResourceIdentifier [6]  IA5String,
 312       //   ...
 313       while (general_names.size() > 0) {
 314         base::StringPiece url;
 315         if (GetElement(&general_names, kContextSpecific | 6, &url)) {
 316           tmp_urls_out.push_back(url);
 317         } else {
 318           if (!GetElement(&general_names, kAny, NULL))
 319             return false;
 320         }
 321       }
 322     }
 323   }
 324
 325   urls_out->swap(tmp_urls_out);
 326   return true;
 327 }
 328
 329 } // namespace asn1
 330
 331 } // namespace net