mcs/class/System/System.Security.Cryptography.X509Certificates/X509Chain.cs

   1 //
   2 // System.Security.Cryptography.X509Certificates.X509Chain
   3 //
   4 // Author:
   5 //      Sebastien Pouliot  <sebastien@ximian.com>
   6 //
   7 // (C) 2003 Motus Technologies Inc. (http://www.motus.com)
   8 // Copyright (C) 2004-2006 Novell Inc. (http://www.novell.com)
   9 // Copyright (C) 2011 Xamarin Inc. (http://www.xamarin.com)
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining
  12 // a copy of this software and associated documentation files (the
  13 // "Software"), to deal in the Software without restriction, including
  14 // without limitation the rights to use, copy, modify, merge, publish,
  15 // distribute, sublicense, and/or sell copies of the Software, and to
  16 // permit persons to whom the Software is furnished to do so, subject to
  17 // the following conditions:
  18 //
  19 // The above copyright notice and this permission notice shall be
  20 // included in all copies or substantial portions of the Software.
  21 //
  22 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  23 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  24 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  25 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  26 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  27 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  28 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  29 //
  30
  31 #if SECURITY_DEP || MOONLIGHT
  32
  33 using System.Collections;
  34 using System.Text;
  35
  36 using MX = Mono.Security.X509;
  37
  38 namespace System.Security.Cryptography.X509Certificates {
  39
  40         public class X509Chain {
  41
  42                 private StoreLocation location;
  43                 private X509ChainElementCollection elements;
  44                 private X509ChainPolicy policy;
  45                 private X509ChainStatus[] status;
  46
  47                 static X509ChainStatus[] Empty = new X509ChainStatus [0];
  48
  49                 // RFC3280 variables
  50                 private int max_path_length;
  51                 private X500DistinguishedName working_issuer_name;
  52 //              private string working_public_key_algorithm;
  53                 private AsymmetricAlgorithm working_public_key;
  54
  55                 // other flags
  56                 private X509ChainElement bce_restriction;
  57
  58                 // constructors
  59
  60                 public X509Chain ()
  61                         : this (false)
  62                 {
  63                 }
  64
  65                 public X509Chain (bool useMachineContext)
  66                 {
  67                         location = useMachineContext ? StoreLocation.LocalMachine : StoreLocation.CurrentUser;
  68                         elements = new X509ChainElementCollection ();
  69                         policy = new X509ChainPolicy ();
  70                 }
  71
  72                 [MonoTODO ("Mono's X509Chain is fully managed. All handles are invalid.")]
  73                 public X509Chain (IntPtr chainContext)
  74                 {
  75                         // CryptoAPI compatibility (unmanaged handle)
  76                         throw new NotSupportedException ();
  77                 }
  78
  79                 // properties
  80
  81                 [MonoTODO ("Mono's X509Chain is fully managed. Always returns IntPtr.Zero.")]
  82                 public IntPtr ChainContext {
  83                         get { return IntPtr.Zero; }
  84                 }
  85
  86                 public X509ChainElementCollection ChainElements {
  87                         get { return elements; }
  88                 }
  89
  90                 public X509ChainPolicy ChainPolicy {
  91                         get { return policy; }
  92                         set { policy = value; }
  93                 }
  94
  95                 public X509ChainStatus[] ChainStatus {
  96                         get {
  97                                 if (status == null)
  98                                         return Empty;
  99                                 return status;
 100                         }
 101                 }
 102
 103                 // methods
 104
 105                 [MonoTODO ("Not totally RFC3280 compliant, but neither is MS implementation...")]
 106                 public bool Build (X509Certificate2 certificate)
 107                 {
 108                         if (certificate == null)
 109                                 throw new ArgumentException ("certificate");
 110
 111                         Reset ();
 112                         X509ChainStatusFlags flag;
 113                         try {
 114                                 flag = BuildChainFrom (certificate);
 115                                 ValidateChain (flag);
 116                         }
 117                         catch (CryptographicException ce) {
 118                                 throw new ArgumentException ("certificate", ce);
 119                         }
 120
 121                         X509ChainStatusFlags total = X509ChainStatusFlags.NoError;
 122                         ArrayList list = new ArrayList ();
 123                         // build "global" ChainStatus from the ChainStatus of every ChainElements
 124                         foreach (X509ChainElement ce in elements) {
 125                                 foreach (X509ChainStatus cs in ce.ChainElementStatus) {
 126                                         // we MUST avoid duplicates in the "global" list
 127                                         if ((total & cs.Status) != cs.Status) {
 128                                                 list.Add (cs);
 129                                                 total |= cs.Status;
 130                                         }
 131                                 }
 132                         }
 133                         // and if required add some
 134                         if (flag != X509ChainStatusFlags.NoError) {
 135                                 list.Insert (0, new X509ChainStatus (flag));
 136                         }
 137                         status = (X509ChainStatus[]) list.ToArray (typeof (X509ChainStatus));
 138
 139                         // (fast path) this ignore everything we have checked
 140                         if ((status.Length == 0) || (ChainPolicy.VerificationFlags == X509VerificationFlags.AllFlags))
 141                                 return true;
 142
 143                         bool result = true;
 144                         // now check if exclude some verification for the "end result" (boolean)
 145                         foreach (X509ChainStatus cs in status) {
 146                                 switch (cs.Status) {
 147                                 case X509ChainStatusFlags.UntrustedRoot:
 148                                 case X509ChainStatusFlags.PartialChain:
 149                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.AllowUnknownCertificateAuthority) != 0);
 150                                         break;
 151                                 case X509ChainStatusFlags.NotTimeValid:
 152                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeValid) != 0);
 153                                         break;
 154                                 // FIXME - from here we needs new test cases for all cases
 155                                 case X509ChainStatusFlags.NotTimeNested:
 156                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeNested) != 0);
 157                                         break;
 158                                 case X509ChainStatusFlags.InvalidBasicConstraints:
 159                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidBasicConstraints) != 0);
 160                                         break;
 161                                 case X509ChainStatusFlags.InvalidPolicyConstraints:
 162                                 case X509ChainStatusFlags.NoIssuanceChainPolicy:
 163                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidPolicy) != 0);
 164                                         break;
 165                                 case X509ChainStatusFlags.InvalidNameConstraints:
 166                                 case X509ChainStatusFlags.HasNotSupportedNameConstraint:
 167                                 case X509ChainStatusFlags.HasNotPermittedNameConstraint:
 168                                 case X509ChainStatusFlags.HasExcludedNameConstraint:
 169                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidName) != 0);
 170                                         break;
 171                                 case X509ChainStatusFlags.InvalidExtension:
 172                                         // not sure ?!?
 173                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
 174                                         break;
 175                                 //
 176                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreRootRevocationUnknown) != 0)
 177                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreEndRevocationUnknown) != 0)
 178                                 case X509ChainStatusFlags.CtlNotTimeValid:
 179                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlNotTimeValid) != 0);
 180                                         break;
 181                                 case X509ChainStatusFlags.CtlNotSignatureValid:
 182                                         // ?
 183                                         break;
 184                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlSignerRevocationUnknown) != 0);
 185                                 case X509ChainStatusFlags.CtlNotValidForUsage:
 186                                         // FIXME - does IgnoreWrongUsage apply to CTL (it doesn't have Ctl in it's name like the others)
 187                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
 188                                         break;
 189                                 default:
 190                                         result = false;
 191                                         break;
 192                                 }
 193                                 // once we have one failure there's no need to check further
 194                                 if (!result)
 195                                         return false;
 196                         }
 197
 198                         // every "problem" was excluded
 199                         return true;
 200                 }
 201
 202                 public void Reset ()
 203                 {
 204                         // note: this call doesn't Reset the X509ChainPolicy
 205                         if ((status != null) && (status.Length != 0))
 206                                 status = null;
 207                         if (elements.Count > 0)
 208                                 elements.Clear ();
 209                         if (user_root_store != null) {
 210                                 user_root_store.Close ();
 211                                 user_root_store = null;
 212                         }
 213                         if (root_store != null) {
 214                                 root_store.Close ();
 215                                 root_store = null;
 216                         }
 217                         if (user_ca_store != null) {
 218                                 user_ca_store.Close ();
 219                                 user_ca_store = null;
 220                         }
 221                         if (ca_store != null) {
 222                                 ca_store.Close ();
 223                                 ca_store = null;
 224                         }
 225                         roots = null;
 226                         cas = null;
 227                         collection = null;
 228                         bce_restriction = null;
 229                         working_public_key = null;
 230                 }
 231
 232                 // static methods
 233
 234                 public static X509Chain Create ()
 235                 {
 236                         return (X509Chain) CryptoConfig.CreateFromName ("X509Chain");
 237                 }
 238
 239                 // private stuff
 240
 241                 private X509Certificate2Collection roots;
 242                 private X509Certificate2Collection cas;
 243                 private X509Store root_store;
 244                 private X509Store ca_store;
 245                 private X509Store user_root_store;
 246                 private X509Store user_ca_store;
 247
 248                 private X509Certificate2Collection Roots {
 249                         get {
 250                                 if (roots == null) {
 251                                         X509Certificate2Collection c = new X509Certificate2Collection ();
 252                                         X509Store store = LMRootStore;
 253                                         if (location == StoreLocation.CurrentUser)
 254                                                 c.AddRange (UserRootStore.Certificates);
 255                                         c.AddRange (store.Certificates);
 256                                         roots = c;
 257                                 }
 258                                 return roots;
 259                         }
 260                 }
 261
 262                 private X509Certificate2Collection CertificateAuthorities {
 263                         get {
 264                                 if (cas == null) {
 265                                         X509Certificate2Collection c = new X509Certificate2Collection ();
 266                                         X509Store store = LMCAStore;
 267                                         if (location == StoreLocation.CurrentUser)
 268                                                 c.AddRange (UserCAStore.Certificates);
 269                                         c.AddRange (store.Certificates);
 270                                         cas = c;
 271                                 }
 272                                 return cas;
 273                         }
 274                 }
 275
 276                 private X509Store LMRootStore {
 277                         get {
 278                                 if (root_store == null) {
 279                                         root_store = new X509Store (StoreName.Root, StoreLocation.LocalMachine);
 280                                         try {
 281                                                 root_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 282                                         } catch {
 283                                         }
 284                                 }
 285                                 return root_store;
 286                         }
 287                 }
 288
 289                 private X509Store UserRootStore {
 290                         get {
 291                                 if (user_root_store == null) {
 292                                         user_root_store = new X509Store (StoreName.Root, StoreLocation.CurrentUser);
 293                                         try {
 294                                                 user_root_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 295                                         } catch {
 296                                         }
 297                                 }
 298                                 return user_root_store;
 299                         }
 300                 }
 301
 302                 private X509Store LMCAStore {
 303                         get {
 304                                 if (ca_store == null) {
 305                                         ca_store = new X509Store (StoreName.CertificateAuthority, StoreLocation.LocalMachine);
 306                                         try {
 307                                                 ca_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 308                                         } catch {
 309                                         }
 310                                 }
 311                                 return ca_store;
 312                         }
 313                 }
 314
 315                 private X509Store UserCAStore {
 316                         get {
 317                                 if (user_ca_store == null) {
 318                                         user_ca_store = new X509Store (StoreName.CertificateAuthority, StoreLocation.CurrentUser);
 319                                         try {
 320                                                 user_ca_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 321                                         } catch {
 322                                         }
 323                                 }
 324                                 return user_ca_store;
 325                         }
 326                 }
 327                 // *** certificate chain/path building stuff ***
 328
 329                 private X509Certificate2Collection collection;
 330
 331                 // we search local user (default) or machine certificate store
 332                 // and in the extra certificate supplied in ChainPolicy.ExtraStore
 333                 private X509Certificate2Collection CertificateCollection {
 334                         get {
 335                                 if (collection == null) {
 336                                         collection = new X509Certificate2Collection (ChainPolicy.ExtraStore);
 337                                         collection.AddRange (Roots);
 338                                         collection.AddRange (CertificateAuthorities);
 339                                 }
 340                                 return collection;
 341                         }
 342                 }
 343
 344                 // This is a non-recursive chain/path building algorithm.
 345                 //
 346                 // At this stage we only checks for PartialChain, Cyclic and UntrustedRoot errors are they
 347                 // affect the path building (other errors are verification errors).
 348                 //
 349                 // Note that the order match the one we need to match MS and not the one defined in RFC3280,
 350                 // we also include the trusted root certificate (trust anchor in RFC3280) in the list.
 351                 // (this isn't an issue, just keep that in mind if you look at the source and the RFC)
 352                 private X509ChainStatusFlags BuildChainFrom (X509Certificate2 certificate)
 353                 {
 354                         elements.Add (certificate);
 355
 356                         while (!IsChainComplete (certificate)) {
 357                                 certificate = FindParent (certificate);
 358
 359                                 if (certificate == null)
 360                                         return X509ChainStatusFlags.PartialChain;
 361
 362                                 if (elements.Contains (certificate))
 363                                         return X509ChainStatusFlags.Cyclic;
 364
 365                                 elements.Add (certificate);
 366                         }
 367
 368                         // roots may be supplied (e.g. in the ExtraStore) so we need to confirm their
 369                         // trustiness (what a cute word) in the trusted root collection
 370                         if (!Roots.Contains (certificate))
 371                                 elements [elements.Count - 1].StatusFlags |= X509ChainStatusFlags.UntrustedRoot;
 372
 373                         return X509ChainStatusFlags.NoError;
 374                 }
 375
 376
 377                 private X509Certificate2 SelectBestFromCollection (X509Certificate2 child, X509Certificate2Collection c)
 378                 {
 379                         switch (c.Count) {
 380                         case 0:
 381                                 return null;
 382                         case 1:
 383                                 return c [0];
 384                         default:
 385                                 // multiple candidate, keep only the ones that are still valid
 386                                 X509Certificate2Collection time_valid = c.Find (X509FindType.FindByTimeValid, ChainPolicy.VerificationTime, false);
 387                                 switch (time_valid.Count) {
 388                                 case 0:
 389                                         // that's too restrictive, let's revert and try another thing...
 390                                         time_valid = c;
 391                                         break;
 392                                 case 1:
 393                                         return time_valid [0];
 394                                 default:
 395                                         break;
 396                                 }
 397
 398                                 // again multiple candidates, let's find the AKI that match the SKI (if we have one)
 399                                 string aki = GetAuthorityKeyIdentifier (child);
 400                                 if (String.IsNullOrEmpty (aki)) {
 401                                         return time_valid [0]; // FIXME: out of luck, you get the first one
 402                                 }
 403                                 foreach (X509Certificate2 parent in time_valid) {
 404                                         string ski = GetSubjectKeyIdentifier (parent);
 405                                         // if both id are available then they must match
 406                                         if (aki == ski)
 407                                                 return parent;
 408                                 }
 409                                 return time_valid [0]; // FIXME: out of luck, you get the first one
 410                         }
 411                 }
 412
 413                 private X509Certificate2 FindParent (X509Certificate2 certificate)
 414                 {
 415                         X509Certificate2Collection subset = CertificateCollection.Find (X509FindType.FindBySubjectDistinguishedName, certificate.Issuer, false);
 416                         string aki = GetAuthorityKeyIdentifier (certificate);
 417                         if ((aki != null) && (aki.Length > 0)) {
 418                                 subset.AddRange (CertificateCollection.Find (X509FindType.FindBySubjectKeyIdentifier, aki, false));
 419                         }
 420                         X509Certificate2 parent = SelectBestFromCollection (certificate, subset);
 421                         // if parent==certificate we're looping but it's not (probably) a bug and not a true cyclic (over n certs)
 422                         return certificate.Equals (parent) ? null : parent;
 423                 }
 424
 425                 private bool IsChainComplete (X509Certificate2 certificate)
 426                 {
 427                         // the chain is complete if we have a self-signed certificate
 428                         if (!IsSelfIssued (certificate))
 429                                 return false;
 430
 431                         // we're very limited to what we can do without certificate extensions
 432                         if (certificate.Version < 3)
 433                                 return true;
 434
 435                         // check that Authority Key Identifier == Subject Key Identifier
 436                         // e.g. it will be different if a self-signed certificate is part (not the end) of the chain
 437                         string ski = GetSubjectKeyIdentifier (certificate);
 438                         if (String.IsNullOrEmpty (ski))
 439                                 return true;
 440                         string aki = GetAuthorityKeyIdentifier (certificate);
 441                         if (String.IsNullOrEmpty (aki))
 442                                 return true;
 443                         // if both id are available then they must match
 444                         return (aki == ski);
 445                 }
 446
 447                 // check for "self-issued" certificate - without verifying the signature
 448                 // note that self-issued doesn't always mean it's a root certificate!
 449                 private bool IsSelfIssued (X509Certificate2 certificate)
 450                 {
 451                         return (certificate.Issuer == certificate.Subject);
 452                 }
 453
 454
 455                 // *** certificate chain/path validation stuff ***
 456
 457                 // Currently a subset of RFC3280 (hopefully a full implementation someday)
 458                 private void ValidateChain (X509ChainStatusFlags flag)
 459                 {
 460                         // 'n' should be the root certificate...
 461                         int n = elements.Count - 1;
 462                         X509Certificate2 certificate = elements [n].Certificate;
 463
 464                         // ... and, if so, must be treated outside the chain...
 465                         if (((flag & X509ChainStatusFlags.PartialChain) == 0)) {
 466                                 Process (n);
 467                                 // deal with the case where the chain == the root certificate
 468                                 // (which isn't for RFC3280) part of the chain
 469                                 if (n == 0) {
 470                                         elements [0].UncompressFlags ();
 471                                         return;
 472                                 }
 473                                 // skip the root certificate when processing the chain (in 6.1.3)
 474                                 n--;
 475                         }
 476                         // ... unless the chain is a partial one (then we start with that one)
 477
 478                         // 6.1.1 - Inputs
 479                         // 6.1.1.a - a prospective certificate path of length n (i.e. elements)
 480                         // 6.1.1.b - the current date/time (i.e. ChainPolicy.VerificationTime)
 481                         // 6.1.1.c - user-initial-policy-set (i.e. ChainPolicy.CertificatePolicy)
 482                         // 6.1.1.d - the trust anchor information (i.e. certificate, unless it's a partial chain)
 483                         // 6.1.1.e - initial-policy-mapping-inhibit (NOT SUPPORTED BY THE API)
 484                         // 6.1.1.f - initial-explicit-policy (NOT SUPPORTED BY THE API)
 485                         // 6.1.1.g - initial-any-policy-inhibit (NOT SUPPORTED BY THE API)
 486
 487                         // 6.1.2 - Initialization (incomplete)
 488                         // 6.1.2.a-f - policy stuff, some TODO, some not supported
 489                         // 6.1.2.g - working public key algorithm
 490 //                      working_public_key_algorithm = certificate.PublicKey.Oid.Value;
 491                         // 6.1.2.h-i - our key contains both the "working public key" and "working public key parameters" data
 492                         working_public_key = certificate.PublicKey.Key;
 493                         // 6.1.2.j - working issuer name
 494                         working_issuer_name = certificate.IssuerName;
 495                         // 6.1.2.k - this integer is initialized to n, is decremented for each non-self-issued, certificate and
 496                         //           may be reduced to the value in the path length constraint field
 497                         max_path_length = n;
 498
 499                         // 6.1.3 - Basic Certificate Processing
 500                         // note: loop looks reversed (the list is) but we process this part just like RFC3280 does
 501                         for (int i = n; i > 0; i--) {
 502                                 Process (i);
 503                                 // 6.1.4 - preparation for certificate i+1 (for not with i+1, or i-1 in our loop)
 504                                 PrepareForNextCertificate (i);
 505                         }
 506                         Process (0);
 507
 508                         // 6.1.3.a.3 - revocation checks
 509                         CheckRevocationOnChain (flag);
 510
 511                         // 6.1.5 - Wrap-up procedure
 512                         WrapUp ();
 513                 }
 514
 515                 private void Process (int n)
 516                 {
 517                         X509ChainElement element = elements [n];
 518                         X509Certificate2 certificate = element.Certificate;
 519
 520                         // pre-step: DSA certificates may inherit the parameters of their CA
 521                         if ((n != elements.Count - 1) && (certificate.MonoCertificate.KeyAlgorithm == "1.2.840.10040.4.1")) {
 522                                 if (certificate.MonoCertificate.KeyAlgorithmParameters == null) {
 523                                         X509Certificate2 parent = elements [n+1].Certificate;
 524                                         certificate.MonoCertificate.KeyAlgorithmParameters = parent.MonoCertificate.KeyAlgorithmParameters;
 525                                 }
 526                         }
 527
 528                         bool root = (working_public_key == null);
 529                         // 6.1.3.a.1 - check signature (with special case to deal with root certificates)
 530                         if (!IsSignedWith (certificate, root ? certificate.PublicKey.Key : working_public_key)) {
 531                                 // another special case where only an end-entity is available and can't be verified.
 532                                 // In this case we do not report an invalid signature (since this is unknown)
 533                                 if (root || (n != elements.Count - 1) || IsSelfIssued (certificate)) {
 534                                         element.StatusFlags |= X509ChainStatusFlags.NotSignatureValid;
 535                                 }
 536                         }
 537
 538                         // 6.1.3.a.2 - check validity period
 539                         if ((ChainPolicy.VerificationTime < certificate.NotBefore) ||
 540                                 (ChainPolicy.VerificationTime > certificate.NotAfter)) {
 541                                 element.StatusFlags |= X509ChainStatusFlags.NotTimeValid;
 542                         }
 543                         // TODO - for X509ChainStatusFlags.NotTimeNested (needs global structure)
 544
 545                         // note: most of them don't apply to the root certificate
 546                         if (root) {
 547                                 return;
 548                         }
 549
 550                         // 6.1.3.a.3 - revocation check (we're doing at the last stage)
 551                         // note: you revoke a trusted root by removing it from your trusted store (i.e. no CRL can do this job)
 552
 553                         // 6.1.3.a.4 - check certificate issuer name
 554                         if (!X500DistinguishedName.AreEqual (certificate.IssuerName, working_issuer_name)) {
 555                                 // NOTE: this is not the "right" error flag, but it's the closest one defined
 556                                 element.StatusFlags |= X509ChainStatusFlags.InvalidNameConstraints;
 557                         }
 558
 559                         if (!IsSelfIssued (certificate) && (n != 0)) {
 560                                 // TODO 6.1.3.b - subject name in the permitted_subtrees ...
 561                                 // TODO 6.1.3.c - subject name not within excluded_subtrees...
 562
 563                                 // TODO - check for X509ChainStatusFlags.InvalidNameConstraint
 564                                 // TODO - check for X509ChainStatusFlags.HasNotSupportedNameConstraint
 565                                 // TODO - check for X509ChainStatusFlags.HasNotPermittedNameConstraint
 566                                 // TODO - check for X509ChainStatusFlags.HasExcludedNameConstraint
 567                         }
 568
 569                         // TODO 6.1.3.d - check if certificate policies extension is present
 570                         //if (false) {
 571                                 // TODO - for X509ChainStatusFlags.InvalidPolicyConstraints
 572                                 //      using X509ChainPolicy.ApplicationPolicy and X509ChainPolicy.CertificatePolicy
 573
 574                                 // TODO - check for X509ChainStatusFlags.NoIssuanceChainPolicy
 575
 576                         //} else {
 577                                 // TODO 6.1.3.e - set valid_policy_tree to NULL
 578                         //}
 579
 580                         // TODO 6.1.3.f - verify explict_policy > 0 if valid_policy_tree != NULL
 581                 }
 582
 583                 // CTL == Certificate Trust List / NOT SUPPORTED
 584                 // TODO - check for X509ChainStatusFlags.CtlNotTimeValid
 585                 // TODO - check for X509ChainStatusFlags.CtlNotSignatureValid
 586                 // TODO - check for X509ChainStatusFlags.CtlNotValidForUsage
 587
 588                 private void PrepareForNextCertificate (int n)
 589                 {
 590                         X509ChainElement element = elements [n];
 591                         X509Certificate2 certificate = element.Certificate;
 592
 593                         // TODO 6.1.4.a-b
 594
 595                         // 6.1.4.c
 596                         working_issuer_name = certificate.SubjectName;
 597                         // 6.1.4.d-e - our key includes both the public key and it's parameters
 598                         working_public_key = certificate.PublicKey.Key;
 599                         // 6.1.4.f
 600 //                      working_public_key_algorithm = certificate.PublicKey.Oid.Value;
 601
 602                         // TODO 6.1.4.g-j
 603
 604                         // 6.1.4.k - Verify that the certificate is a CA certificate
 605                         X509BasicConstraintsExtension bce = (certificate.Extensions["2.5.29.19"] as X509BasicConstraintsExtension);
 606                         if (bce != null) {
 607                                 if (!bce.CertificateAuthority) {
 608                                         element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 609                                 }
 610                         } else if (certificate.Version >= 3) {
 611                                 // recent (v3+) CA certificates must include BCE
 612                                 element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 613                         }
 614
 615                         // 6.1.4.l - if the certificate isn't self-issued...
 616                         if (!IsSelfIssued (certificate)) {
 617                                 // ... verify that max_path_length > 0
 618                                 if (max_path_length > 0) {
 619                                         max_path_length--;
 620                                 } else {
 621                                         // to match MS the reported status must be against the certificate
 622                                         // with the BCE and not where the path is too long. It also means
 623                                         // that this condition has to be reported only once
 624                                         if (bce_restriction != null) {
 625                                                 bce_restriction.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 626                                         }
 627                                 }
 628                         }
 629
 630                         // 6.1.4.m - if pathLengthConstraint is present...
 631                         if ((bce != null) && (bce.HasPathLengthConstraint)) {
 632                                 // ... and is less that max_path_length, set max_path_length to it's value
 633                                 if (bce.PathLengthConstraint < max_path_length) {
 634                                         max_path_length = bce.PathLengthConstraint;
 635                                         bce_restriction = element;
 636                                 }
 637                         }
 638
 639                         // 6.1.4.n - if key usage extension is present...
 640                         X509KeyUsageExtension kue = (certificate.Extensions["2.5.29.15"] as X509KeyUsageExtension);
 641                         if (kue != null) {
 642                                 // ... verify keyCertSign is set
 643                                 X509KeyUsageFlags success = X509KeyUsageFlags.KeyCertSign;
 644                                 if ((kue.KeyUsages & success) != success)
 645                                         element.StatusFlags |= X509ChainStatusFlags.NotValidForUsage;
 646                         }
 647
 648                         // 6.1.4.o - recognize and process other critical extension present in the certificate
 649                         ProcessCertificateExtensions (element);
 650                 }
 651
 652                 private void WrapUp ()
 653                 {
 654                         X509ChainElement element = elements [0];
 655                         X509Certificate2 certificate = element.Certificate;
 656
 657                         // 6.1.5.a - TODO if certificate n (our 0) wasn't self issued and explicit_policy != 0
 658                         if (IsSelfIssued (certificate)) {
 659                                 // TODO... decrement explicit_policy by 1
 660                         }
 661
 662                         // 6.1.5.b - TODO
 663
 664                         // 6.1.5.c,d,e - not required by the X509Chain implementation
 665
 666                         // 6.1.5.f - recognize and process other critical extension present in the certificate
 667                         ProcessCertificateExtensions (element);
 668
 669                         // 6.1.5.g - TODO
 670
 671                         // uncompressed the flags into several elements
 672                         for (int i = elements.Count - 1; i >= 0; i--) {
 673                                 elements [i].UncompressFlags ();
 674                         }
 675                 }
 676
 677                 private void ProcessCertificateExtensions (X509ChainElement element)
 678                 {
 679                         foreach (X509Extension ext in element.Certificate.Extensions) {
 680                                 if (ext.Critical) {
 681                                         switch (ext.Oid.Value) {
 682                                         case "2.5.29.15": // X509KeyUsageExtension
 683                                         case "2.5.29.19": // X509BasicConstraintsExtension
 684                                                 // we processed this extension
 685                                                 break;
 686                                         default:
 687                                                 // note: Under Windows XP MS implementation seems to ignore
 688                                                 // certificate with unknown critical extensions.
 689                                                 element.StatusFlags |= X509ChainStatusFlags.InvalidExtension;
 690                                                 break;
 691                                         }
 692                                 }
 693                         }
 694                 }
 695
 696                 private bool IsSignedWith (X509Certificate2 signed, AsymmetricAlgorithm pubkey)
 697                 {
 698                         if (pubkey == null)
 699                                 return false;
 700                         // Sadly X509Certificate2 doesn't expose the signature nor the tbs (to be signed) structure
 701                         MX.X509Certificate mx = signed.MonoCertificate;
 702                         return (mx.VerifySignature (pubkey));
 703                 }
 704
 705                 private string GetSubjectKeyIdentifier (X509Certificate2 certificate)
 706                 {
 707                         X509SubjectKeyIdentifierExtension ski = (certificate.Extensions["2.5.29.14"] as X509SubjectKeyIdentifierExtension);
 708                         return (ski == null) ? String.Empty : ski.SubjectKeyIdentifier;
 709                 }
 710
 711                 // System.dll v2 doesn't have a class to deal with the AuthorityKeyIdentifier extension
 712                 static string GetAuthorityKeyIdentifier (X509Certificate2 certificate)
 713                 {
 714                         return GetAuthorityKeyIdentifier (certificate.MonoCertificate.Extensions ["2.5.29.35"]);
 715                 }
 716
 717                 // but anyway System.dll v2 doesn't expose CRL in any way so...
 718                 static string GetAuthorityKeyIdentifier (MX.X509Crl crl)
 719                 {
 720                         return GetAuthorityKeyIdentifier (crl.Extensions ["2.5.29.35"]);
 721                 }
 722
 723                 static string GetAuthorityKeyIdentifier (MX.X509Extension ext)
 724                 {
 725                         if (ext == null)
 726                                 return String.Empty;
 727                         MX.Extensions.AuthorityKeyIdentifierExtension aki = new MX.Extensions.AuthorityKeyIdentifierExtension (ext);
 728                         byte[] id = aki.Identifier;
 729                         if (id == null)
 730                                 return String.Empty;
 731                         StringBuilder sb = new StringBuilder ();
 732                         foreach (byte b in id)
 733                                 sb.Append (b.ToString ("X02"));
 734                         return sb.ToString ();
 735                 }
 736
 737                 // we check the revocation only once we have built the complete chain
 738                 private void CheckRevocationOnChain (X509ChainStatusFlags flag)
 739                 {
 740                         bool partial = ((flag & X509ChainStatusFlags.PartialChain) != 0);
 741                         bool online;
 742
 743                         switch (ChainPolicy.RevocationMode) {
 744                         case X509RevocationMode.Online:
 745                                 // default
 746                                 online = true;
 747                                 break;
 748                         case X509RevocationMode.Offline:
 749                                 online = false;
 750                                 break;
 751                         case X509RevocationMode.NoCheck:
 752                                 return;
 753                         default:
 754                                 throw new InvalidOperationException (Locale.GetText ("Invalid revocation mode."));
 755                         }
 756
 757                         bool unknown = partial;
 758                         // from the root down to the end-entity
 759                         for (int i = elements.Count - 1; i >= 0; i--) {
 760                                 bool check = true;
 761
 762                                 switch (ChainPolicy.RevocationFlag) {
 763                                 case X509RevocationFlag.EndCertificateOnly:
 764                                         check = (i == 0);
 765                                         break;
 766                                 case X509RevocationFlag.EntireChain:
 767                                         check = true;
 768                                         break;
 769                                 case X509RevocationFlag.ExcludeRoot:
 770                                         // default
 771                                         check = (i != (elements.Count - 1));
 772                                         // anyway, who's gonna sign that the root is invalid ?
 773                                         break;
 774                                 }
 775
 776                                 X509ChainElement element = elements [i];
 777
 778                                 // we can't assume the revocation status if the certificate is bad (e.g. invalid signature)
 779                                 if (!unknown)
 780                                         unknown |= ((element.StatusFlags & X509ChainStatusFlags.NotSignatureValid) != 0);
 781
 782                                 if (unknown) {
 783                                         // we can skip the revocation checks as we can't be sure of them anyway
 784                                         element.StatusFlags |= X509ChainStatusFlags.RevocationStatusUnknown;
 785                                         element.StatusFlags |= X509ChainStatusFlags.OfflineRevocation;
 786                                 } else if (check && !partial && !IsSelfIssued (element.Certificate)) {
 787                                         // check for revocation (except for the trusted root and self-issued certs)
 788                                         element.StatusFlags |= CheckRevocation (element.Certificate, i+1, online);
 789                                         // if revoked, then all others following in the chain are unknown...
 790                                         unknown |= ((element.StatusFlags & X509ChainStatusFlags.Revoked) != 0);
 791                                 }
 792                         }
 793                 }
 794
 795                 // This isn't how RFC3280 (section 6.3) deals with CRL, but then we don't (yet) support DP, deltas...
 796                 private X509ChainStatusFlags CheckRevocation (X509Certificate2 certificate, int ca, bool online)
 797                 {
 798                         X509ChainStatusFlags result = X509ChainStatusFlags.RevocationStatusUnknown;
 799                         X509ChainElement element = elements [ca];
 800                         X509Certificate2 ca_cert = element.Certificate;
 801
 802                         // find the CRL from the "right" CA
 803                         while (IsSelfIssued (ca_cert) && (ca < elements.Count - 1)) {
 804                                 // try with this self-issued
 805                                 result = CheckRevocation (certificate, ca_cert, online);
 806                                 if (result != X509ChainStatusFlags.RevocationStatusUnknown)
 807                                         break;
 808                                 ca++;
 809                                 element = elements [ca];
 810                                 ca_cert = element.Certificate;
 811                         }
 812                         if (result == X509ChainStatusFlags.RevocationStatusUnknown)
 813                                 result = CheckRevocation (certificate, ca_cert, online);
 814                         return result;
 815                 }
 816
 817                 private X509ChainStatusFlags CheckRevocation (X509Certificate2 certificate, X509Certificate2 ca_cert, bool online)
 818                 {
 819                         // change this if/when we support OCSP
 820                         X509KeyUsageExtension kue = (ca_cert.Extensions["2.5.29.15"] as X509KeyUsageExtension);
 821                         if (kue != null) {
 822                                 // ... verify CrlSign is set
 823                                 X509KeyUsageFlags success = X509KeyUsageFlags.CrlSign;
 824                                 if ((kue.KeyUsages & success) != success) {
 825                                         // FIXME - we should try to find an alternative CA that has the CrlSign bit
 826                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 827                                 }
 828                         }
 829
 830                         MX.X509Crl crl = FindCrl (ca_cert);
 831
 832                         if ((crl == null) && online) {
 833                                 // FIXME - download and install new CRL
 834                                 // then you get a second chance
 835                                 // crl = FindCrl (ca_cert, ref valid, ref out_of_date);
 836
 837                                 // We need to get the subjectAltName and an URI from there (or use OCSP)
 838                                 // X509KeyUsageExtension subjectAltName = (ca_cert.Extensions["2.5.29.17"] as X509KeyUsageExtension);
 839                         }
 840
 841                         if (crl != null) {
 842                                 // validate the digital signature on the CRL using the CA public key
 843                                 // note #1: we can't use X509Crl.VerifySignature(X509Certificate) because it duplicates
 844                                 // checks and we loose the "why" of the failure
 845                                 // note #2: we do this before other tests as an invalid signature could be a hacked CRL
 846                                 // (so anything within can't be trusted)
 847                                 if (!crl.VerifySignature (ca_cert.PublicKey.Key)) {
 848                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 849                                 }
 850
 851                                 MX.X509Crl.X509CrlEntry entry = crl.GetCrlEntry (certificate.MonoCertificate);
 852                                 if (entry != null) {
 853                                         // We have an entry for this CRL that includes an unknown CRITICAL extension
 854                                         // See [X.509 7.3] NOTE 4
 855                                         if (!ProcessCrlEntryExtensions (entry))
 856                                                 return X509ChainStatusFlags.Revoked;
 857
 858                                         // FIXME - a little more is involved
 859                                         if (entry.RevocationDate <= ChainPolicy.VerificationTime)
 860                                                 return X509ChainStatusFlags.Revoked;
 861                                 }
 862
 863                                 // are we overdue for a CRL update ? if so we can't be sure of any certificate status
 864                                 if (crl.NextUpdate < ChainPolicy.VerificationTime)
 865                                         return X509ChainStatusFlags.RevocationStatusUnknown | X509ChainStatusFlags.OfflineRevocation;
 866
 867                                 // we have a CRL that includes an unknown CRITICAL extension
 868                                 // we put this check at the end so we do not "hide" any Revoked flags
 869                                 if (!ProcessCrlExtensions (crl)) {
 870                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 871                                 }
 872                         } else {
 873                                 return X509ChainStatusFlags.RevocationStatusUnknown;
 874                         }
 875
 876                         return X509ChainStatusFlags.NoError;
 877                 }
 878
 879                 static MX.X509Crl CheckCrls (string subject, string ski, ArrayList crls)
 880                 {
 881                         foreach (MX.X509Crl crl in crls) {
 882                                 if (crl.IssuerName == subject && (ski.Length == 0 || ski == GetAuthorityKeyIdentifier (crl)))
 883                                         return crl;
 884                         }
 885                         return null; // No CRL found
 886                 }
 887
 888                 private MX.X509Crl FindCrl (X509Certificate2 caCertificate)
 889                 {
 890                         string subject = caCertificate.SubjectName.Decode (X500DistinguishedNameFlags.None);
 891                         string ski = GetSubjectKeyIdentifier (caCertificate);
 892
 893                         // consider that the LocalMachine directories could not exists... and cannot be created by the user
 894                         MX.X509Crl result = (LMCAStore.Store == null) ? null : CheckCrls (subject, ski, LMCAStore.Store.Crls);
 895                         if (result != null)
 896                                 return result;
 897                         if (location == StoreLocation.CurrentUser) {
 898                                 result = CheckCrls (subject, ski, UserCAStore.Store.Crls);
 899                                 if (result != null)
 900                                         return result;
 901                         }
 902
 903                         // consider that the LocalMachine directories could not exists... and cannot be created by the user
 904                         result = (LMRootStore.Store == null) ? null : CheckCrls (subject, ski, LMRootStore.Store.Crls);
 905                         if (result != null)
 906                                 return result;
 907                         if (location == StoreLocation.CurrentUser) {
 908                                 result = CheckCrls (subject, ski, UserRootStore.Store.Crls);
 909                                 if (result != null)
 910                                         return result;
 911                         }
 912                         return null;
 913                 }
 914
 915                 private bool ProcessCrlExtensions (MX.X509Crl crl)
 916                 {
 917                         foreach (MX.X509Extension ext in crl.Extensions) {
 918                                 if (ext.Critical) {
 919                                         switch (ext.Oid) {
 920                                         case "2.5.29.20": // cRLNumber
 921                                         case "2.5.29.35": // authorityKeyIdentifier
 922                                                 // we processed/know about this extension
 923                                                 break;
 924                                         default:
 925                                                 return false;
 926                                         }
 927                                 }
 928                         }
 929                         return true;
 930                 }
 931
 932                 private bool ProcessCrlEntryExtensions (MX.X509Crl.X509CrlEntry entry)
 933                 {
 934                         foreach (MX.X509Extension ext in entry.Extensions) {
 935                                 if (ext.Critical) {
 936                                         switch (ext.Oid) {
 937                                         case "2.5.29.21": // cRLReason
 938                                                 // we processed/know about this extension
 939                                                 break;
 940                                         default:
 941                                                 return false;
 942                                         }
 943                                 }
 944                         }
 945                         return true;
 946                 }
 947         }
 948 }
 949 #else
 950 namespace System.Security.Cryptography.X509Certificates {
 951         public class X509Chain {
 952                 public bool Build (X509Certificate2 cert)
 953                 {
 954                         return false;
 955                 }
 956         }
 957 }
 958 #endif
 959