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
  32
  33 extern alias MonoSecurity;
  34
  35 using System.Collections;
  36 using System.Text;
  37
  38 using MX = MonoSecurity::Mono.Security.X509;
  39
  40 namespace System.Security.Cryptography.X509Certificates {
  41
  42         public class X509Chain {
  43
  44                 private StoreLocation location;
  45                 private X509ChainElementCollection elements;
  46                 private X509ChainPolicy policy;
  47                 private X509ChainStatus[] status;
  48
  49                 static X509ChainStatus[] Empty = new X509ChainStatus [0];
  50
  51                 // RFC3280 variables
  52                 private int max_path_length;
  53                 private X500DistinguishedName working_issuer_name;
  54 //              private string working_public_key_algorithm;
  55                 private AsymmetricAlgorithm working_public_key;
  56
  57                 // other flags
  58                 private X509ChainElement bce_restriction;
  59
  60                 // constructors
  61
  62                 public X509Chain ()
  63                         : this (false)
  64                 {
  65                 }
  66
  67                 public X509Chain (bool useMachineContext)
  68                 {
  69                         location = useMachineContext ? StoreLocation.LocalMachine : StoreLocation.CurrentUser;
  70                         elements = new X509ChainElementCollection ();
  71                         policy = new X509ChainPolicy ();
  72                 }
  73
  74                 [MonoTODO ("Mono's X509Chain is fully managed. All handles are invalid.")]
  75                 public X509Chain (IntPtr chainContext)
  76                 {
  77                         // CryptoAPI compatibility (unmanaged handle)
  78                         throw new NotSupportedException ();
  79                 }
  80
  81                 // properties
  82
  83                 [MonoTODO ("Mono's X509Chain is fully managed. Always returns IntPtr.Zero.")]
  84                 public IntPtr ChainContext {
  85                         get { return IntPtr.Zero; }
  86                 }
  87
  88                 public X509ChainElementCollection ChainElements {
  89                         get { return elements; }
  90                 }
  91
  92                 public X509ChainPolicy ChainPolicy {
  93                         get { return policy; }
  94                         set { policy = value; }
  95                 }
  96
  97                 public X509ChainStatus[] ChainStatus {
  98                         get {
  99                                 if (status == null)
 100                                         return Empty;
 101                                 return status;
 102                         }
 103                 }
 104
 105                 // methods
 106
 107                 [MonoTODO ("Not totally RFC3280 compliant, but neither is MS implementation...")]
 108                 public bool Build (X509Certificate2 certificate)
 109                 {
 110                         if (certificate == null)
 111                                 throw new ArgumentException ("certificate");
 112
 113                         Reset ();
 114                         X509ChainStatusFlags flag;
 115                         try {
 116                                 flag = BuildChainFrom (certificate);
 117                                 ValidateChain (flag);
 118                         }
 119                         catch (CryptographicException ce) {
 120                                 throw new ArgumentException ("certificate", ce);
 121                         }
 122
 123                         X509ChainStatusFlags total = X509ChainStatusFlags.NoError;
 124                         ArrayList list = new ArrayList ();
 125                         // build "global" ChainStatus from the ChainStatus of every ChainElements
 126                         foreach (X509ChainElement ce in elements) {
 127                                 foreach (X509ChainStatus cs in ce.ChainElementStatus) {
 128                                         // we MUST avoid duplicates in the "global" list
 129                                         if ((total & cs.Status) != cs.Status) {
 130                                                 list.Add (cs);
 131                                                 total |= cs.Status;
 132                                         }
 133                                 }
 134                         }
 135                         // and if required add some
 136                         if (flag != X509ChainStatusFlags.NoError) {
 137                                 list.Insert (0, new X509ChainStatus (flag));
 138                         }
 139                         status = (X509ChainStatus[]) list.ToArray (typeof (X509ChainStatus));
 140
 141                         // (fast path) this ignore everything we have checked
 142                         if ((status.Length == 0) || (ChainPolicy.VerificationFlags == X509VerificationFlags.AllFlags))
 143                                 return true;
 144
 145                         bool result = true;
 146                         // now check if exclude some verification for the "end result" (boolean)
 147                         foreach (X509ChainStatus cs in status) {
 148                                 switch (cs.Status) {
 149                                 case X509ChainStatusFlags.UntrustedRoot:
 150                                 case X509ChainStatusFlags.PartialChain:
 151                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.AllowUnknownCertificateAuthority) != 0);
 152                                         break;
 153                                 case X509ChainStatusFlags.NotTimeValid:
 154                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeValid) != 0);
 155                                         break;
 156                                 // FIXME - from here we needs new test cases for all cases
 157                                 case X509ChainStatusFlags.NotTimeNested:
 158                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeNested) != 0);
 159                                         break;
 160                                 case X509ChainStatusFlags.InvalidBasicConstraints:
 161                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidBasicConstraints) != 0);
 162                                         break;
 163                                 case X509ChainStatusFlags.InvalidPolicyConstraints:
 164                                 case X509ChainStatusFlags.NoIssuanceChainPolicy:
 165                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidPolicy) != 0);
 166                                         break;
 167                                 case X509ChainStatusFlags.InvalidNameConstraints:
 168                                 case X509ChainStatusFlags.HasNotSupportedNameConstraint:
 169                                 case X509ChainStatusFlags.HasNotPermittedNameConstraint:
 170                                 case X509ChainStatusFlags.HasExcludedNameConstraint:
 171                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidName) != 0);
 172                                         break;
 173                                 case X509ChainStatusFlags.InvalidExtension:
 174                                         // not sure ?!?
 175                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
 176                                         break;
 177                                 //
 178                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreRootRevocationUnknown) != 0)
 179                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreEndRevocationUnknown) != 0)
 180                                 case X509ChainStatusFlags.CtlNotTimeValid:
 181                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlNotTimeValid) != 0);
 182                                         break;
 183                                 case X509ChainStatusFlags.CtlNotSignatureValid:
 184                                         // ?
 185                                         break;
 186                                 //      ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlSignerRevocationUnknown) != 0);
 187                                 case X509ChainStatusFlags.CtlNotValidForUsage:
 188                                         // FIXME - does IgnoreWrongUsage apply to CTL (it doesn't have Ctl in it's name like the others)
 189                                         result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
 190                                         break;
 191                                 default:
 192                                         result = false;
 193                                         break;
 194                                 }
 195                                 // once we have one failure there's no need to check further
 196                                 if (!result)
 197                                         return false;
 198                         }
 199
 200                         // every "problem" was excluded
 201                         return true;
 202                 }
 203
 204                 public void Reset ()
 205                 {
 206                         // note: this call doesn't Reset the X509ChainPolicy
 207                         if ((status != null) && (status.Length != 0))
 208                                 status = null;
 209                         if (elements.Count > 0)
 210                                 elements.Clear ();
 211                         if (user_root_store != null) {
 212                                 user_root_store.Close ();
 213                                 user_root_store = null;
 214                         }
 215                         if (root_store != null) {
 216                                 root_store.Close ();
 217                                 root_store = null;
 218                         }
 219                         if (user_ca_store != null) {
 220                                 user_ca_store.Close ();
 221                                 user_ca_store = null;
 222                         }
 223                         if (ca_store != null) {
 224                                 ca_store.Close ();
 225                                 ca_store = null;
 226                         }
 227                         roots = null;
 228                         cas = null;
 229                         collection = null;
 230                         bce_restriction = null;
 231                         working_public_key = null;
 232                 }
 233
 234                 // static methods
 235
 236                 public static X509Chain Create ()
 237                 {
 238                         return (X509Chain) CryptoConfig.CreateFromName ("X509Chain");
 239                 }
 240
 241                 // private stuff
 242
 243                 private X509Certificate2Collection roots;
 244                 private X509Certificate2Collection cas;
 245                 private X509Store root_store;
 246                 private X509Store ca_store;
 247                 private X509Store user_root_store;
 248                 private X509Store user_ca_store;
 249
 250                 private X509Certificate2Collection Roots {
 251                         get {
 252                                 if (roots == null) {
 253                                         X509Certificate2Collection c = new X509Certificate2Collection ();
 254                                         X509Store store = LMRootStore;
 255                                         if (location == StoreLocation.CurrentUser)
 256                                                 c.AddRange (UserRootStore.Certificates);
 257                                         c.AddRange (store.Certificates);
 258                                         roots = c;
 259                                 }
 260                                 return roots;
 261                         }
 262                 }
 263
 264                 private X509Certificate2Collection CertificateAuthorities {
 265                         get {
 266                                 if (cas == null) {
 267                                         X509Certificate2Collection c = new X509Certificate2Collection ();
 268                                         X509Store store = LMCAStore;
 269                                         if (location == StoreLocation.CurrentUser)
 270                                                 c.AddRange (UserCAStore.Certificates);
 271                                         c.AddRange (store.Certificates);
 272                                         cas = c;
 273                                 }
 274                                 return cas;
 275                         }
 276                 }
 277
 278                 private X509Store LMRootStore {
 279                         get {
 280                                 if (root_store == null) {
 281                                         root_store = new X509Store (StoreName.Root, StoreLocation.LocalMachine);
 282                                         try {
 283                                                 root_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 284                                         } catch {
 285                                         }
 286                                 }
 287                                 return root_store;
 288                         }
 289                 }
 290
 291                 private X509Store UserRootStore {
 292                         get {
 293                                 if (user_root_store == null) {
 294                                         user_root_store = new X509Store (StoreName.Root, StoreLocation.CurrentUser);
 295                                         try {
 296                                                 user_root_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 297                                         } catch {
 298                                         }
 299                                 }
 300                                 return user_root_store;
 301                         }
 302                 }
 303
 304                 private X509Store LMCAStore {
 305                         get {
 306                                 if (ca_store == null) {
 307                                         ca_store = new X509Store (StoreName.CertificateAuthority, StoreLocation.LocalMachine);
 308                                         try {
 309                                                 ca_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 310                                         } catch {
 311                                         }
 312                                 }
 313                                 return ca_store;
 314                         }
 315                 }
 316
 317                 private X509Store UserCAStore {
 318                         get {
 319                                 if (user_ca_store == null) {
 320                                         user_ca_store = new X509Store (StoreName.CertificateAuthority, StoreLocation.CurrentUser);
 321                                         try {
 322                                                 user_ca_store.Open (OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);
 323                                         } catch {
 324                                         }
 325                                 }
 326                                 return user_ca_store;
 327                         }
 328                 }
 329                 // *** certificate chain/path building stuff ***
 330
 331                 private X509Certificate2Collection collection;
 332
 333                 // we search local user (default) or machine certificate store
 334                 // and in the extra certificate supplied in ChainPolicy.ExtraStore
 335                 private X509Certificate2Collection CertificateCollection {
 336                         get {
 337                                 if (collection == null) {
 338                                         collection = new X509Certificate2Collection (ChainPolicy.ExtraStore);
 339                                         collection.AddRange (Roots);
 340                                         collection.AddRange (CertificateAuthorities);
 341                                 }
 342                                 return collection;
 343                         }
 344                 }
 345
 346                 // This is a non-recursive chain/path building algorithm.
 347                 //
 348                 // At this stage we only checks for PartialChain, Cyclic and UntrustedRoot errors are they
 349                 // affect the path building (other errors are verification errors).
 350                 //
 351                 // Note that the order match the one we need to match MS and not the one defined in RFC3280,
 352                 // we also include the trusted root certificate (trust anchor in RFC3280) in the list.
 353                 // (this isn't an issue, just keep that in mind if you look at the source and the RFC)
 354                 private X509ChainStatusFlags BuildChainFrom (X509Certificate2 certificate)
 355                 {
 356                         elements.Add (certificate);
 357
 358                         while (!IsChainComplete (certificate)) {
 359                                 certificate = FindParent (certificate);
 360
 361                                 if (certificate == null)
 362                                         return X509ChainStatusFlags.PartialChain;
 363
 364                                 if (elements.Contains (certificate))
 365                                         return X509ChainStatusFlags.Cyclic;
 366
 367                                 elements.Add (certificate);
 368                         }
 369
 370                         // roots may be supplied (e.g. in the ExtraStore) so we need to confirm their
 371                         // trustiness (what a cute word) in the trusted root collection
 372                         if (!Roots.Contains (certificate))
 373                                 elements [elements.Count - 1].StatusFlags |= X509ChainStatusFlags.UntrustedRoot;
 374
 375                         return X509ChainStatusFlags.NoError;
 376                 }
 377
 378
 379                 private X509Certificate2 SelectBestFromCollection (X509Certificate2 child, X509Certificate2Collection c)
 380                 {
 381                         switch (c.Count) {
 382                         case 0:
 383                                 return null;
 384                         case 1:
 385                                 return c [0];
 386                         default:
 387                                 // multiple candidate, keep only the ones that are still valid
 388                                 X509Certificate2Collection time_valid = c.Find (X509FindType.FindByTimeValid, ChainPolicy.VerificationTime, false);
 389                                 switch (time_valid.Count) {
 390                                 case 0:
 391                                         // that's too restrictive, let's revert and try another thing...
 392                                         time_valid = c;
 393                                         break;
 394                                 case 1:
 395                                         return time_valid [0];
 396                                 default:
 397                                         break;
 398                                 }
 399
 400                                 // again multiple candidates, let's find the AKI that match the SKI (if we have one)
 401                                 string aki = GetAuthorityKeyIdentifier (child);
 402                                 if (String.IsNullOrEmpty (aki)) {
 403                                         return time_valid [0]; // FIXME: out of luck, you get the first one
 404                                 }
 405                                 foreach (X509Certificate2 parent in time_valid) {
 406                                         string ski = GetSubjectKeyIdentifier (parent);
 407                                         // if both id are available then they must match
 408                                         if (aki == ski)
 409                                                 return parent;
 410                                 }
 411                                 return time_valid [0]; // FIXME: out of luck, you get the first one
 412                         }
 413                 }
 414
 415                 private X509Certificate2 FindParent (X509Certificate2 certificate)
 416                 {
 417                         X509Certificate2Collection subset = CertificateCollection.Find (X509FindType.FindBySubjectDistinguishedName, certificate.Issuer, false);
 418                         string aki = GetAuthorityKeyIdentifier (certificate);
 419                         if ((aki != null) && (aki.Length > 0)) {
 420                                 subset.AddRange (CertificateCollection.Find (X509FindType.FindBySubjectKeyIdentifier, aki, false));
 421                         }
 422                         X509Certificate2 parent = SelectBestFromCollection (certificate, subset);
 423                         // if parent==certificate we're looping but it's not (probably) a bug and not a true cyclic (over n certs)
 424                         return certificate.Equals (parent) ? null : parent;
 425                 }
 426
 427                 private bool IsChainComplete (X509Certificate2 certificate)
 428                 {
 429                         // the chain is complete if we have a self-signed certificate
 430                         if (!IsSelfIssued (certificate))
 431                                 return false;
 432
 433                         // we're very limited to what we can do without certificate extensions
 434                         if (certificate.Version < 3)
 435                                 return true;
 436
 437                         // check that Authority Key Identifier == Subject Key Identifier
 438                         // e.g. it will be different if a self-signed certificate is part (not the end) of the chain
 439                         string ski = GetSubjectKeyIdentifier (certificate);
 440                         if (String.IsNullOrEmpty (ski))
 441                                 return true;
 442                         string aki = GetAuthorityKeyIdentifier (certificate);
 443                         if (String.IsNullOrEmpty (aki))
 444                                 return true;
 445                         // if both id are available then they must match
 446                         return (aki == ski);
 447                 }
 448
 449                 // check for "self-issued" certificate - without verifying the signature
 450                 // note that self-issued doesn't always mean it's a root certificate!
 451                 private bool IsSelfIssued (X509Certificate2 certificate)
 452                 {
 453                         return (certificate.Issuer == certificate.Subject);
 454                 }
 455
 456
 457                 // *** certificate chain/path validation stuff ***
 458
 459                 // Currently a subset of RFC3280 (hopefully a full implementation someday)
 460                 private void ValidateChain (X509ChainStatusFlags flag)
 461                 {
 462                         // 'n' should be the root certificate...
 463                         int n = elements.Count - 1;
 464                         X509Certificate2 certificate = elements [n].Certificate;
 465
 466                         // ... and, if so, must be treated outside the chain...
 467                         if (((flag & X509ChainStatusFlags.PartialChain) == 0)) {
 468                                 Process (n);
 469                                 // deal with the case where the chain == the root certificate
 470                                 // (which isn't for RFC3280) part of the chain
 471                                 if (n == 0) {
 472                                         elements [0].UncompressFlags ();
 473                                         return;
 474                                 }
 475                                 // skip the root certificate when processing the chain (in 6.1.3)
 476                                 n--;
 477                         }
 478                         // ... unless the chain is a partial one (then we start with that one)
 479
 480                         // 6.1.1 - Inputs
 481                         // 6.1.1.a - a prospective certificate path of length n (i.e. elements)
 482                         // 6.1.1.b - the current date/time (i.e. ChainPolicy.VerificationTime)
 483                         // 6.1.1.c - user-initial-policy-set (i.e. ChainPolicy.CertificatePolicy)
 484                         // 6.1.1.d - the trust anchor information (i.e. certificate, unless it's a partial chain)
 485                         // 6.1.1.e - initial-policy-mapping-inhibit (NOT SUPPORTED BY THE API)
 486                         // 6.1.1.f - initial-explicit-policy (NOT SUPPORTED BY THE API)
 487                         // 6.1.1.g - initial-any-policy-inhibit (NOT SUPPORTED BY THE API)
 488
 489                         // 6.1.2 - Initialization (incomplete)
 490                         // 6.1.2.a-f - policy stuff, some TODO, some not supported
 491                         // 6.1.2.g - working public key algorithm
 492 //                      working_public_key_algorithm = certificate.PublicKey.Oid.Value;
 493                         // 6.1.2.h-i - our key contains both the "working public key" and "working public key parameters" data
 494                         working_public_key = certificate.PublicKey.Key;
 495                         // 6.1.2.j - working issuer name
 496                         working_issuer_name = certificate.IssuerName;
 497                         // 6.1.2.k - this integer is initialized to n, is decremented for each non-self-issued, certificate and
 498                         //           may be reduced to the value in the path length constraint field
 499                         max_path_length = n;
 500
 501                         // 6.1.3 - Basic Certificate Processing
 502                         // note: loop looks reversed (the list is) but we process this part just like RFC3280 does
 503                         for (int i = n; i > 0; i--) {
 504                                 Process (i);
 505                                 // 6.1.4 - preparation for certificate i+1 (for not with i+1, or i-1 in our loop)
 506                                 PrepareForNextCertificate (i);
 507                         }
 508                         Process (0);
 509
 510                         // 6.1.3.a.3 - revocation checks
 511                         CheckRevocationOnChain (flag);
 512
 513                         // 6.1.5 - Wrap-up procedure
 514                         WrapUp ();
 515                 }
 516
 517                 private void Process (int n)
 518                 {
 519                         X509ChainElement element = elements [n];
 520                         X509Certificate2 certificate = element.Certificate;
 521
 522                         // pre-step: DSA certificates may inherit the parameters of their CA
 523                         if ((n != elements.Count - 1) && (certificate.MonoCertificate.KeyAlgorithm == "1.2.840.10040.4.1")) {
 524                                 if (certificate.MonoCertificate.KeyAlgorithmParameters == null) {
 525                                         X509Certificate2 parent = elements [n+1].Certificate;
 526                                         certificate.MonoCertificate.KeyAlgorithmParameters = parent.MonoCertificate.KeyAlgorithmParameters;
 527                                 }
 528                         }
 529
 530                         bool root = (working_public_key == null);
 531                         // 6.1.3.a.1 - check signature (with special case to deal with root certificates)
 532                         if (!IsSignedWith (certificate, root ? certificate.PublicKey.Key : working_public_key)) {
 533                                 // another special case where only an end-entity is available and can't be verified.
 534                                 // In this case we do not report an invalid signature (since this is unknown)
 535                                 if (root || (n != elements.Count - 1) || IsSelfIssued (certificate)) {
 536                                         element.StatusFlags |= X509ChainStatusFlags.NotSignatureValid;
 537                                 }
 538                         }
 539
 540                         // 6.1.3.a.2 - check validity period
 541                         if ((ChainPolicy.VerificationTime < certificate.NotBefore) ||
 542                                 (ChainPolicy.VerificationTime > certificate.NotAfter)) {
 543                                 element.StatusFlags |= X509ChainStatusFlags.NotTimeValid;
 544                         }
 545                         // TODO - for X509ChainStatusFlags.NotTimeNested (needs global structure)
 546
 547                         // note: most of them don't apply to the root certificate
 548                         if (root) {
 549                                 return;
 550                         }
 551
 552                         // 6.1.3.a.3 - revocation check (we're doing at the last stage)
 553                         // note: you revoke a trusted root by removing it from your trusted store (i.e. no CRL can do this job)
 554
 555                         // 6.1.3.a.4 - check certificate issuer name
 556                         if (!X500DistinguishedName.AreEqual (certificate.IssuerName, working_issuer_name)) {
 557                                 // NOTE: this is not the "right" error flag, but it's the closest one defined
 558                                 element.StatusFlags |= X509ChainStatusFlags.InvalidNameConstraints;
 559                         }
 560
 561                         if (!IsSelfIssued (certificate) && (n != 0)) {
 562                                 // TODO 6.1.3.b - subject name in the permitted_subtrees ...
 563                                 // TODO 6.1.3.c - subject name not within excluded_subtrees...
 564
 565                                 // TODO - check for X509ChainStatusFlags.InvalidNameConstraint
 566                                 // TODO - check for X509ChainStatusFlags.HasNotSupportedNameConstraint
 567                                 // TODO - check for X509ChainStatusFlags.HasNotPermittedNameConstraint
 568                                 // TODO - check for X509ChainStatusFlags.HasExcludedNameConstraint
 569                         }
 570
 571                         // TODO 6.1.3.d - check if certificate policies extension is present
 572                         //if (false) {
 573                                 // TODO - for X509ChainStatusFlags.InvalidPolicyConstraints
 574                                 //      using X509ChainPolicy.ApplicationPolicy and X509ChainPolicy.CertificatePolicy
 575
 576                                 // TODO - check for X509ChainStatusFlags.NoIssuanceChainPolicy
 577
 578                         //} else {
 579                                 // TODO 6.1.3.e - set valid_policy_tree to NULL
 580                         //}
 581
 582                         // TODO 6.1.3.f - verify explict_policy > 0 if valid_policy_tree != NULL
 583                 }
 584
 585                 // CTL == Certificate Trust List / NOT SUPPORTED
 586                 // TODO - check for X509ChainStatusFlags.CtlNotTimeValid
 587                 // TODO - check for X509ChainStatusFlags.CtlNotSignatureValid
 588                 // TODO - check for X509ChainStatusFlags.CtlNotValidForUsage
 589
 590                 private void PrepareForNextCertificate (int n)
 591                 {
 592                         X509ChainElement element = elements [n];
 593                         X509Certificate2 certificate = element.Certificate;
 594
 595                         // TODO 6.1.4.a-b
 596
 597                         // 6.1.4.c
 598                         working_issuer_name = certificate.SubjectName;
 599                         // 6.1.4.d-e - our key includes both the public key and it's parameters
 600                         working_public_key = certificate.PublicKey.Key;
 601                         // 6.1.4.f
 602 //                      working_public_key_algorithm = certificate.PublicKey.Oid.Value;
 603
 604                         // TODO 6.1.4.g-j
 605
 606                         // 6.1.4.k - Verify that the certificate is a CA certificate
 607                         X509BasicConstraintsExtension bce = (certificate.Extensions["2.5.29.19"] as X509BasicConstraintsExtension);
 608                         if (bce != null) {
 609                                 if (!bce.CertificateAuthority) {
 610                                         element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 611                                 }
 612                         } else if (certificate.Version >= 3) {
 613                                 // recent (v3+) CA certificates must include BCE
 614                                 element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 615                         }
 616
 617                         // 6.1.4.l - if the certificate isn't self-issued...
 618                         if (!IsSelfIssued (certificate)) {
 619                                 // ... verify that max_path_length > 0
 620                                 if (max_path_length > 0) {
 621                                         max_path_length--;
 622                                 } else {
 623                                         // to match MS the reported status must be against the certificate
 624                                         // with the BCE and not where the path is too long. It also means
 625                                         // that this condition has to be reported only once
 626                                         if (bce_restriction != null) {
 627                                                 bce_restriction.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
 628                                         }
 629                                 }
 630                         }
 631
 632                         // 6.1.4.m - if pathLengthConstraint is present...
 633                         if ((bce != null) && (bce.HasPathLengthConstraint)) {
 634                                 // ... and is less that max_path_length, set max_path_length to it's value
 635                                 if (bce.PathLengthConstraint < max_path_length) {
 636                                         max_path_length = bce.PathLengthConstraint;
 637                                         bce_restriction = element;
 638                                 }
 639                         }
 640
 641                         // 6.1.4.n - if key usage extension is present...
 642                         X509KeyUsageExtension kue = (certificate.Extensions["2.5.29.15"] as X509KeyUsageExtension);
 643                         if (kue != null) {
 644                                 // ... verify keyCertSign is set
 645                                 X509KeyUsageFlags success = X509KeyUsageFlags.KeyCertSign;
 646                                 if ((kue.KeyUsages & success) != success)
 647                                         element.StatusFlags |= X509ChainStatusFlags.NotValidForUsage;
 648                         }
 649
 650                         // 6.1.4.o - recognize and process other critical extension present in the certificate
 651                         ProcessCertificateExtensions (element);
 652                 }
 653
 654                 private void WrapUp ()
 655                 {
 656                         X509ChainElement element = elements [0];
 657                         X509Certificate2 certificate = element.Certificate;
 658
 659                         // 6.1.5.a - TODO if certificate n (our 0) wasn't self issued and explicit_policy != 0
 660                         if (IsSelfIssued (certificate)) {
 661                                 // TODO... decrement explicit_policy by 1
 662                         }
 663
 664                         // 6.1.5.b - TODO
 665
 666                         // 6.1.5.c,d,e - not required by the X509Chain implementation
 667
 668                         // 6.1.5.f - recognize and process other critical extension present in the certificate
 669                         ProcessCertificateExtensions (element);
 670
 671                         // 6.1.5.g - TODO
 672
 673                         // uncompressed the flags into several elements
 674                         for (int i = elements.Count - 1; i >= 0; i--) {
 675                                 elements [i].UncompressFlags ();
 676                         }
 677                 }
 678
 679                 private void ProcessCertificateExtensions (X509ChainElement element)
 680                 {
 681                         foreach (X509Extension ext in element.Certificate.Extensions) {
 682                                 if (ext.Critical) {
 683                                         switch (ext.Oid.Value) {
 684                                         case "2.5.29.15": // X509KeyUsageExtension
 685                                         case "2.5.29.19": // X509BasicConstraintsExtension
 686                                                 // we processed this extension
 687                                                 break;
 688                                         default:
 689                                                 // note: Under Windows XP MS implementation seems to ignore
 690                                                 // certificate with unknown critical extensions.
 691                                                 element.StatusFlags |= X509ChainStatusFlags.InvalidExtension;
 692                                                 break;
 693                                         }
 694                                 }
 695                         }
 696                 }
 697
 698                 private bool IsSignedWith (X509Certificate2 signed, AsymmetricAlgorithm pubkey)
 699                 {
 700                         if (pubkey == null)
 701                                 return false;
 702                         // Sadly X509Certificate2 doesn't expose the signature nor the tbs (to be signed) structure
 703                         MX.X509Certificate mx = signed.MonoCertificate;
 704                         return (mx.VerifySignature (pubkey));
 705                 }
 706
 707                 private string GetSubjectKeyIdentifier (X509Certificate2 certificate)
 708                 {
 709                         X509SubjectKeyIdentifierExtension ski = (certificate.Extensions["2.5.29.14"] as X509SubjectKeyIdentifierExtension);
 710                         return (ski == null) ? String.Empty : ski.SubjectKeyIdentifier;
 711                 }
 712
 713                 // System.dll v2 doesn't have a class to deal with the AuthorityKeyIdentifier extension
 714                 static string GetAuthorityKeyIdentifier (X509Certificate2 certificate)
 715                 {
 716                         return GetAuthorityKeyIdentifier (certificate.MonoCertificate.Extensions ["2.5.29.35"]);
 717                 }
 718
 719                 // but anyway System.dll v2 doesn't expose CRL in any way so...
 720                 static string GetAuthorityKeyIdentifier (MX.X509Crl crl)
 721                 {
 722                         return GetAuthorityKeyIdentifier (crl.Extensions ["2.5.29.35"]);
 723                 }
 724
 725                 static string GetAuthorityKeyIdentifier (MX.X509Extension ext)
 726                 {
 727                         if (ext == null)
 728                                 return String.Empty;
 729                         MX.Extensions.AuthorityKeyIdentifierExtension aki = new MX.Extensions.AuthorityKeyIdentifierExtension (ext);
 730                         byte[] id = aki.Identifier;
 731                         if (id == null)
 732                                 return String.Empty;
 733                         StringBuilder sb = new StringBuilder ();
 734                         foreach (byte b in id)
 735                                 sb.Append (b.ToString ("X02"));
 736                         return sb.ToString ();
 737                 }
 738
 739                 // we check the revocation only once we have built the complete chain
 740                 private void CheckRevocationOnChain (X509ChainStatusFlags flag)
 741                 {
 742                         bool partial = ((flag & X509ChainStatusFlags.PartialChain) != 0);
 743                         bool online;
 744
 745                         switch (ChainPolicy.RevocationMode) {
 746                         case X509RevocationMode.Online:
 747                                 // default
 748                                 online = true;
 749                                 break;
 750                         case X509RevocationMode.Offline:
 751                                 online = false;
 752                                 break;
 753                         case X509RevocationMode.NoCheck:
 754                                 return;
 755                         default:
 756                                 throw new InvalidOperationException (Locale.GetText ("Invalid revocation mode."));
 757                         }
 758
 759                         bool unknown = partial;
 760                         // from the root down to the end-entity
 761                         for (int i = elements.Count - 1; i >= 0; i--) {
 762                                 bool check = true;
 763
 764                                 switch (ChainPolicy.RevocationFlag) {
 765                                 case X509RevocationFlag.EndCertificateOnly:
 766                                         check = (i == 0);
 767                                         break;
 768                                 case X509RevocationFlag.EntireChain:
 769                                         check = true;
 770                                         break;
 771                                 case X509RevocationFlag.ExcludeRoot:
 772                                         // default
 773                                         check = (i != (elements.Count - 1));
 774                                         // anyway, who's gonna sign that the root is invalid ?
 775                                         break;
 776                                 }
 777
 778                                 X509ChainElement element = elements [i];
 779
 780                                 // we can't assume the revocation status if the certificate is bad (e.g. invalid signature)
 781                                 if (!unknown)
 782                                         unknown |= ((element.StatusFlags & X509ChainStatusFlags.NotSignatureValid) != 0);
 783
 784                                 if (unknown) {
 785                                         // we can skip the revocation checks as we can't be sure of them anyway
 786                                         element.StatusFlags |= X509ChainStatusFlags.RevocationStatusUnknown;
 787                                         element.StatusFlags |= X509ChainStatusFlags.OfflineRevocation;
 788                                 } else if (check && !partial && !IsSelfIssued (element.Certificate)) {
 789                                         // check for revocation (except for the trusted root and self-issued certs)
 790                                         element.StatusFlags |= CheckRevocation (element.Certificate, i+1, online);
 791                                         // if revoked, then all others following in the chain are unknown...
 792                                         unknown |= ((element.StatusFlags & X509ChainStatusFlags.Revoked) != 0);
 793                                 }
 794                         }
 795                 }
 796
 797                 // This isn't how RFC3280 (section 6.3) deals with CRL, but then we don't (yet) support DP, deltas...
 798                 private X509ChainStatusFlags CheckRevocation (X509Certificate2 certificate, int ca, bool online)
 799                 {
 800                         X509ChainStatusFlags result = X509ChainStatusFlags.RevocationStatusUnknown;
 801                         X509ChainElement element = elements [ca];
 802                         X509Certificate2 ca_cert = element.Certificate;
 803
 804                         // find the CRL from the "right" CA
 805                         while (IsSelfIssued (ca_cert) && (ca < elements.Count - 1)) {
 806                                 // try with this self-issued
 807                                 result = CheckRevocation (certificate, ca_cert, online);
 808                                 if (result != X509ChainStatusFlags.RevocationStatusUnknown)
 809                                         break;
 810                                 ca++;
 811                                 element = elements [ca];
 812                                 ca_cert = element.Certificate;
 813                         }
 814                         if (result == X509ChainStatusFlags.RevocationStatusUnknown)
 815                                 result = CheckRevocation (certificate, ca_cert, online);
 816                         return result;
 817                 }
 818
 819                 private X509ChainStatusFlags CheckRevocation (X509Certificate2 certificate, X509Certificate2 ca_cert, bool online)
 820                 {
 821                         // change this if/when we support OCSP
 822                         X509KeyUsageExtension kue = (ca_cert.Extensions["2.5.29.15"] as X509KeyUsageExtension);
 823                         if (kue != null) {
 824                                 // ... verify CrlSign is set
 825                                 X509KeyUsageFlags success = X509KeyUsageFlags.CrlSign;
 826                                 if ((kue.KeyUsages & success) != success) {
 827                                         // FIXME - we should try to find an alternative CA that has the CrlSign bit
 828                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 829                                 }
 830                         }
 831
 832                         MX.X509Crl crl = FindCrl (ca_cert);
 833
 834                         if ((crl == null) && online) {
 835                                 // FIXME - download and install new CRL
 836                                 // then you get a second chance
 837                                 // crl = FindCrl (ca_cert, ref valid, ref out_of_date);
 838
 839                                 // We need to get the subjectAltName and an URI from there (or use OCSP)
 840                                 // X509KeyUsageExtension subjectAltName = (ca_cert.Extensions["2.5.29.17"] as X509KeyUsageExtension);
 841                         }
 842
 843                         if (crl != null) {
 844                                 // validate the digital signature on the CRL using the CA public key
 845                                 // note #1: we can't use X509Crl.VerifySignature(X509Certificate) because it duplicates
 846                                 // checks and we loose the "why" of the failure
 847                                 // note #2: we do this before other tests as an invalid signature could be a hacked CRL
 848                                 // (so anything within can't be trusted)
 849                                 if (!crl.VerifySignature (ca_cert.PublicKey.Key)) {
 850                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 851                                 }
 852
 853                                 MX.X509Crl.X509CrlEntry entry = crl.GetCrlEntry (certificate.MonoCertificate);
 854                                 if (entry != null) {
 855                                         // We have an entry for this CRL that includes an unknown CRITICAL extension
 856                                         // See [X.509 7.3] NOTE 4
 857                                         if (!ProcessCrlEntryExtensions (entry))
 858                                                 return X509ChainStatusFlags.Revoked;
 859
 860                                         // FIXME - a little more is involved
 861                                         if (entry.RevocationDate <= ChainPolicy.VerificationTime)
 862                                                 return X509ChainStatusFlags.Revoked;
 863                                 }
 864
 865                                 // are we overdue for a CRL update ? if so we can't be sure of any certificate status
 866                                 if (crl.NextUpdate < ChainPolicy.VerificationTime)
 867                                         return X509ChainStatusFlags.RevocationStatusUnknown | X509ChainStatusFlags.OfflineRevocation;
 868
 869                                 // we have a CRL that includes an unknown CRITICAL extension
 870                                 // we put this check at the end so we do not "hide" any Revoked flags
 871                                 if (!ProcessCrlExtensions (crl)) {
 872                                         return X509ChainStatusFlags.RevocationStatusUnknown;
 873                                 }
 874                         } else {
 875                                 return X509ChainStatusFlags.RevocationStatusUnknown;
 876                         }
 877
 878                         return X509ChainStatusFlags.NoError;
 879                 }
 880
 881                 static MX.X509Crl CheckCrls (string subject, string ski, MX.X509Store store)
 882                 {
 883                         if (store == null)
 884                                 return null;
 885
 886                         var crls = store.Crls;
 887                         foreach (MX.X509Crl crl in crls) {
 888                                 if (crl.IssuerName == subject && (ski.Length == 0 || ski == GetAuthorityKeyIdentifier (crl)))
 889                                         return crl;
 890                         }
 891                         return null; // No CRL found
 892                 }
 893
 894                 private MX.X509Crl FindCrl (X509Certificate2 caCertificate)
 895                 {
 896                         string subject = caCertificate.SubjectName.Decode (X500DistinguishedNameFlags.None);
 897                         string ski = GetSubjectKeyIdentifier (caCertificate);
 898
 899                         // consider that the LocalMachine directories could not exists... and cannot be created by the user
 900                         MX.X509Crl result = CheckCrls (subject, ski, LMCAStore.Store);
 901                         if (result != null)
 902                                 return result;
 903                         if (location == StoreLocation.CurrentUser) {
 904                                 result = CheckCrls (subject, ski, UserCAStore.Store);
 905                                 if (result != null)
 906                                         return result;
 907                         }
 908
 909                         // consider that the LocalMachine directories could not exists... and cannot be created by the user
 910                         result = CheckCrls (subject, ski, LMRootStore.Store);
 911                         if (result != null)
 912                                 return result;
 913                         if (location == StoreLocation.CurrentUser) {
 914                                 result = CheckCrls (subject, ski, UserRootStore.Store);
 915                                 if (result != null)
 916                                         return result;
 917                         }
 918                         return null;
 919                 }
 920
 921                 private bool ProcessCrlExtensions (MX.X509Crl crl)
 922                 {
 923                         foreach (MX.X509Extension ext in crl.Extensions) {
 924                                 if (ext.Critical) {
 925                                         switch (ext.Oid) {
 926                                         case "2.5.29.20": // cRLNumber
 927                                         case "2.5.29.35": // authorityKeyIdentifier
 928                                                 // we processed/know about this extension
 929                                                 break;
 930                                         default:
 931                                                 return false;
 932                                         }
 933                                 }
 934                         }
 935                         return true;
 936                 }
 937
 938                 private bool ProcessCrlEntryExtensions (MX.X509Crl.X509CrlEntry entry)
 939                 {
 940                         foreach (MX.X509Extension ext in entry.Extensions) {
 941                                 if (ext.Critical) {
 942                                         switch (ext.Oid) {
 943                                         case "2.5.29.21": // cRLReason
 944                                                 // we processed/know about this extension
 945                                                 break;
 946                                         default:
 947                                                 return false;
 948                                         }
 949                                 }
 950                         }
 951                         return true;
 952                 }
 953         }
 954 }
 955 #else
 956 namespace System.Security.Cryptography.X509Certificates {
 957         public class X509Chain {
 958                 public bool Build (X509Certificate2 cert)
 959                 {
 960                         return false;
 961                 }
 962         }
 963 }
 964 #endif
 965