private bool IsChainComplete(BCX509Certificate2 certificate)
{
// the chain is complete if we have a self-signed certificate
if (!IsSelfIssued(certificate))
{
return(false);
}
// we're very limited to what we can do without certificate extensions
//if (certificate.Version < 3)
// return true;
// check that Authority Key Identifier == Subject Key Identifier
// e.g. it will be different if a self-signed certificate is part (not the end) of the chain
string ski = GetSubjectKeyIdentifier(certificate);
if (String.IsNullOrEmpty(ski))
{
return(true);
}
string aki = GetAuthorityKeyIdentifier(certificate);
if (String.IsNullOrEmpty(aki))
{
return(true);
}
// if both id are available then they must match
return(aki == ski);
}
private string GetSubjectKeyIdentifier(BCX509Certificate2 certificate)
{
//SubjectKeyIdentifier ski = (certificate.Extensions["2.5.29.14"] as SubjectKeyIdentifier);
SubjectKeyIdentifier ski = SubjectKeyIdentifier.GetInstance(certificate.CertificateStructure.TbsCertificate.Extensions.GetExtension(X509Extensions.SubjectKeyIdentifier));
return((ski == null) ? String.Empty : Hex.ToHexString(ski.GetKeyIdentifier()));
}
private void WrapUp()
{
X509ChainElement element = elements[0];
BCX509Certificate2 certificate = element.BCCertificate;
// 6.1.5.a - TODO if certificate n (our 0) wasn't self issued and explicit_policy != 0
if (IsSelfIssued(certificate))
{
// TODO... decrement explicit_policy by 1
}
// 6.1.5.b - TODO
// 6.1.5.c,d,e - not required by the X509Chain implementation
// 6.1.5.f - recognize and process other critical extension present in the certificate
ProcessCertificateExtensions(element);
// 6.1.5.g - TODO
// uncompressed the flags into several elements
for (int i = elements.Count - 1; i >= 0; i--)
{
elements[i].UncompressFlags();
}
}
// This is a non-recursive chain/path building algorithm.
//
// At this stage we only checks for PartialChain, Cyclic and UntrustedRoot errors are they
// affect the path building (other errors are verification errors).
//
// Note that the order match the one we need to match MS and not the one defined in RFC3280,
// we also include the trusted root certificate (trust anchor in RFC3280) in the list.
// (this isn't an issue, just keep that in mind if you look at the source and the RFC)
private X509ChainStatusFlags BuildChainFrom(BCX509Certificate2 certificate)
{
elements.Add(certificate);
while (!IsChainComplete(certificate))
{
certificate = FindParent(certificate);
if (certificate == null)
{
return(X509ChainStatusFlags.PartialChain);
}
if (elements.Contains(certificate))
{
return(X509ChainStatusFlags.Cyclic);
}
elements.Add(certificate);
}
// roots may be supplied (e.g. in the ExtraStore) so we need to confirm their
// trustiness (what a cute word) in the trusted root collection
if (!Roots.Contains(certificate))
{
elements[elements.Count - 1].StatusFlags |= X509ChainStatusFlags.UntrustedRoot;
}
return(X509ChainStatusFlags.NoError);
}
// This isn't how RFC3280 (section 6.3) deals with CRL, but then we don't (yet) support DP, deltas...
private X509ChainStatusFlags CheckRevocation(BCX509Certificate2 certificate, int ca, bool online)
{
X509ChainStatusFlags result = X509ChainStatusFlags.RevocationStatusUnknown;
X509ChainElement element = elements[ca];
BCX509Certificate2 ca_cert = element.BCCertificate;
// find the CRL from the "right" CA
while (IsSelfIssued(ca_cert) && (ca < elements.Count - 1))
{
// try with this self-issued
result = CheckRevocation(certificate, ca_cert, online);
if (result != X509ChainStatusFlags.RevocationStatusUnknown)
{
break;
}
ca++;
element = elements[ca];
ca_cert = element.BCCertificate;
}
if (result == X509ChainStatusFlags.RevocationStatusUnknown)
{
result = CheckRevocation(certificate, ca_cert, online);
}
return(result);
}
// *** certificate chain/path validation stuff ***
// Currently a subset of RFC3280 (hopefully a full implementation someday)
private void ValidateChain(X509ChainStatusFlags flag)
{
// 'n' should be the root certificate...
int n = elements.Count - 1;
BCX509Certificate2 certificate = elements[n].BCCertificate;
// ... and, if so, must be treated outside the chain...
if (((flag & X509ChainStatusFlags.PartialChain) == 0))
{
Process(n);
// deal with the case where the chain == the root certificate
// (which isn't for RFC3280) part of the chain
if (n == 0)
{
elements[0].UncompressFlags();
return;
}
// skip the root certificate when processing the chain (in 6.1.3)
n--;
}
// ... unless the chain is a partial one (then we start with that one)
// 6.1.1 - Inputs
// 6.1.1.a - a prospective certificate path of length n (i.e. elements)
// 6.1.1.b - the current date/time (i.e. ChainPolicy.VerificationTime)
// 6.1.1.c - user-initial-policy-set (i.e. ChainPolicy.CertificatePolicy)
// 6.1.1.d - the trust anchor information (i.e. certificate, unless it's a partial chain)
// 6.1.1.e - initial-policy-mapping-inhibit (NOT SUPPORTED BY THE API)
// 6.1.1.f - initial-explicit-policy (NOT SUPPORTED BY THE API)
// 6.1.1.g - initial-any-policy-inhibit (NOT SUPPORTED BY THE API)
// 6.1.2 - Initialization (incomplete)
// 6.1.2.a-f - policy stuff, some TODO, some not supported
// 6.1.2.g - working public key algorithm
// working_public_key_algorithm = certificate.PublicKey.Oid.Value;
// 6.1.2.h-i - our key contains both the "working public key" and "working public key parameters" data
working_public_key = certificate.GetPublicKey();
// 6.1.2.j - working issuer name
working_issuer_name = certificate.IssuerDN;
// 6.1.2.k - this integer is initialized to n, is decremented for each non-self-issued, certificate and
// may be reduced to the value in the path length constraint field
max_path_length = n;
// 6.1.3 - Basic Certificate Processing
// note: loop looks reversed (the list is) but we process this part just like RFC3280 does
for (int i = n; i > 0; i--)
{
Process(i);
// 6.1.4 - preparation for certificate i+1 (for not with i+1, or i-1 in our loop)
PrepareForNextCertificate(i);
}
Process(0);
// 6.1.3.a.3 - revocation checks
CheckRevocationOnChain(flag);
// 6.1.5 - Wrap-up procedure
WrapUp();
}
// System.dll v2 doesn't have a class to deal with the AuthorityKeyIdentifier extension
private static string GetAuthorityKeyIdentifier(BCX509Certificate2 certificate)
{
//return GetAuthorityKeyIdentifier (certificate.Extensions["2.5.29.35"]);
//return GetAuthorityKeyIdentifier (certificate.CertificateStructure.TbsCertificate.Extensions.GetExtension (new Oid ("2.5.29.35")).GetParsedValue () as AuthorityKeyIdentifier);
AuthorityKeyIdentifier ski = AuthorityKeyIdentifier.GetInstance(certificate.CertificateStructure.TbsCertificate.Extensions.GetExtension(X509Extensions.AuthorityKeyIdentifier));
return((ski == null) ? String.Empty : Hex.ToHexString(ski.GetKeyIdentifier()));
}
private BCX509Certificate2 FindParent(BCX509Certificate2 certificate)
{
BCX509CertificateCollection subset = CertificateCollection.Find(BCX509FindType.FindBySubjectDistinguishedName, certificate.IssuerDN, false);
string aki = GetAuthorityKeyIdentifier(certificate);
if ((aki != null) && (aki.Length > 0))
{
subset.AddRange(CertificateCollection.Find(BCX509FindType.FindBySubjectKeyIdentifier, aki, false));
}
BCX509Certificate2 parent = SelectBestFromCollection(certificate, subset);
// if parent==certificate we're looping but it's not (probably) a bug and not a true cyclic (over n certs)
return(certificate.Equals(parent) ? null : parent);
}
private bool IsSignedWith(BCX509Certificate2 signed, AsymmetricAlgorithm pubkey)
{
if (pubkey == null)
{
return(false);
}
try
{
signed.Verify(pubkey);
return(true);
}
catch (Exception)
{
return(false);
}
}
private BCX509Certificate2 SelectBestFromCollection(BCX509Certificate2 child, BCX509CertificateCollection c)
{
switch (c.Count)
{
case 0:
return(null);
case 1:
return(c[0]);
default:
// multiple candidate, keep only the ones that are still valid
BCX509CertificateCollection time_valid = c.Find(BCX509FindType.FindByTimeValid, ChainPolicy.VerificationTime, false);
switch (time_valid.Count)
{
case 0:
// that's too restrictive, let's revert and try another thing...
time_valid = c;
break;
case 1:
return(time_valid[0]);
default:
break;
}
// again multiple candidates, let's find the AKI that match the SKI (if we have one)
string aki = GetAuthorityKeyIdentifier(child);
if (String.IsNullOrEmpty(aki))
{
return(time_valid[0]); // FIXME: out of luck, you get the first one
}
foreach (BCX509Certificate2 parent in time_valid)
{
string ski = GetSubjectKeyIdentifier(parent);
// if both id are available then they must match
if (aki == ski)
{
return(parent);
}
}
return(time_valid[0]); // FIXME: out of luck, you get the first one
}
}
private X509Crl FindCrl(BCX509Certificate2 caCertificate)
{
#if !NETCF
string subject = caCertificate.SubjectDN.Decode(X500DistinguishedNameFlags.None);
string ski = GetSubjectKeyIdentifier(caCertificate);
// consider that the LocalMachine directories could not exists... and cannot be created by the user
X509Crl result = CheckCrls(subject, ski, LMCAStore.Store);
if (result != null)
{
return(result);
}
if (location == StoreLocation.CurrentUser)
{
result = CheckCrls(subject, ski, UserCAStore.Store);
if (result != null)
{
return(result);
}
}
// consider that the LocalMachine directories could not exists... and cannot be created by the user
result = CheckCrls(subject, ski, LMRootStore.Store);
if (result != null)
{
return(result);
}
if (location == StoreLocation.CurrentUser)
{
result = CheckCrls(subject, ski, UserRootStore.Store);
if (result != null)
{
return(result);
}
}
#endif
return(null);
}
// CTL == Certificate Trust List / NOT SUPPORTED
// TODO - check for X509ChainStatusFlags.CtlNotTimeValid
// TODO - check for X509ChainStatusFlags.CtlNotSignatureValid
// TODO - check for X509ChainStatusFlags.CtlNotValidForUsage
private void PrepareForNextCertificate(int n)
{
X509ChainElement element = elements[n];
BCX509Certificate2 certificate = element.BCCertificate;
// TODO 6.1.4.a-b
// 6.1.4.c
working_issuer_name = certificate.SubjectDN;
// 6.1.4.d-e - our key includes both the public key and it's parameters
working_public_key = certificate.GetPublicKey();
// 6.1.4.f
// working_public_key_algorithm = certificate.PublicKey.Oid.Value;
// TODO 6.1.4.g-j
// 6.1.4.k - Verify that the certificate is a CA certificate
//BasicConstraints bce = (certificate.Extensions["2.5.29.19"] as BasicConstraints);
BasicConstraints bce = BasicConstraints.GetInstance(certificate.CertificateStructure.TbsCertificate.Extensions.GetExtension(X509Extensions.BasicConstraints));
if (bce != null)
{
if (!bce.IsCA())
{
element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
}
}
else if (certificate.Version >= 3)
{
// recent (v3+) CA certificates must include BCE
element.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
}
// 6.1.4.l - if the certificate isn't self-issued...
if (!IsSelfIssued(certificate))
{
// ... verify that max_path_length > 0
if (max_path_length > 0)
{
max_path_length--;
}
else
{
// to match MS the reported status must be against the certificate
// with the BCE and not where the path is too long. It also means
// that this condition has to be reported only once
if (bce_restriction != null)
{
bce_restriction.StatusFlags |= X509ChainStatusFlags.InvalidBasicConstraints;
}
}
}
// 6.1.4.m - if pathLengthConstraint is present...
if ((bce != null) && (bce.PathLenConstraint != null))
{
// ... and is less that max_path_length, set max_path_length to it's value
if (bce.PathLenConstraint.IntValue < max_path_length)
{
max_path_length = bce.PathLenConstraint.IntValue;
bce_restriction = element;
}
}
// 6.1.4.n - if key usage extension is present...
//X509KeyUsage kue = (certificate.Extensions["2.5.29.15"] as X509KeyUsage);
KeyUsage kue = KeyUsage.GetInstance(certificate.CertificateStructure.TbsCertificate.Extensions.GetExtension(X509Extensions.KeyUsage));
if (kue != null)
{
// ... verify keyCertSign is set
//KeyUsage success = new KeyUsage(KeyUsage.KeyCertSign);
//if ((kue.KeyUsages & success) != success)
if ((kue.IntValue & KeyUsage.KeyCertSign) != KeyUsage.KeyCertSign)
{
element.StatusFlags |= X509ChainStatusFlags.NotValidForUsage;
}
}
// 6.1.4.o - recognize and process other critical extension present in the certificate
ProcessCertificateExtensions(element);
}
private void Process(int n)
{
X509ChainElement element = elements[n];
BCX509Certificate2 certificate = element.BCCertificate;
// pre-step: DSA certificates may inherit the parameters of their CA
if ((n != elements.Count - 1) && (certificate.SigAlgName == "1.2.840.10040.4.1"))
{
if (certificate.GetPublicKey() == null)
{
BCX509Certificate2 parent = elements[n + 1].BCCertificate;
//certificate.GetPublicKey() = parent.GetPublicKey ();
}
}
bool root = (working_public_key == null);
// 6.1.3.a.1 - check signature (with special case to deal with root certificates)
if (!IsSignedWith(certificate, root ? certificate.GetPublicKey() : working_public_key))
{
// another special case where only an end-entity is available and can't be verified.
// In this case we do not report an invalid signature (since this is unknown)
if (root || (n != elements.Count - 1) || IsSelfIssued(certificate))
{
element.StatusFlags |= X509ChainStatusFlags.NotSignatureValid;
}
}
// 6.1.3.a.2 - check validity period
if ((ChainPolicy.VerificationTime < certificate.NotBefore) || (ChainPolicy.VerificationTime > certificate.NotAfter))
{
element.StatusFlags |= X509ChainStatusFlags.NotTimeValid;
}
// TODO - for X509ChainStatusFlags.NotTimeNested (needs global structure)
// note: most of them don't apply to the root certificate
if (root)
{
return;
}
// 6.1.3.a.3 - revocation check (we're doing at the last stage)
// note: you revoke a trusted root by removing it from your trusted store (i.e. no CRL can do this job)
// 6.1.3.a.4 - check certificate issuer name
if (!certificate.IssuerDN.Equals(working_issuer_name))
{
// NOTE: this is not the "right" error flag, but it's the closest one defined
element.StatusFlags |= X509ChainStatusFlags.InvalidNameConstraints;
}
if (!IsSelfIssued(certificate) && (n != 0))
{
// TODO 6.1.3.b - subject name in the permitted_subtrees ...
// TODO 6.1.3.c - subject name not within excluded_subtrees...
// TODO - check for X509ChainStatusFlags.InvalidNameConstraint
// TODO - check for X509ChainStatusFlags.HasNotSupportedNameConstraint
// TODO - check for X509ChainStatusFlags.HasNotPermittedNameConstraint
// TODO - check for X509ChainStatusFlags.HasExcludedNameConstraint
}
// TODO 6.1.3.d - check if certificate policies extension is present
//if (false) {
// TODO - for X509ChainStatusFlags.InvalidPolicyConstraints
// using X509ChainPolicy.ApplicationPolicy and X509ChainPolicy.CertificatePolicy
// TODO - check for X509ChainStatusFlags.NoIssuanceChainPolicy
//} else {
// TODO 6.1.3.e - set valid_policy_tree to NULL
//}
// TODO 6.1.3.f - verify explict_policy > 0 if valid_policy_tree != NULL
}
// check for "self-issued" certificate - without verifying the signature
// note that self-issued doesn't always mean it's a root certificate!
private bool IsSelfIssued(BCX509Certificate2 certificate)
{
return(certificate.IssuerDN.Equals(certificate.SubjectDN));
}
// methods
public bool Build(BCX509Certificate2 certificate)
{
if (certificate == null)
{
throw new ArgumentException("certificate");
}
Reset();
X509ChainStatusFlags flag;
try
{
flag = BuildChainFrom(certificate);
ValidateChain(flag);
}
catch (CryptographicException ce)
{
throw new ArgumentException("certificate", ce);
}
X509ChainStatusFlags total = X509ChainStatusFlags.NoError;
ArrayList list = new ArrayList();
// build "global" ChainStatus from the ChainStatus of every ChainElements
foreach (X509ChainElement ce in elements)
{
foreach (X509ChainStatus cs in ce.ChainElementStatus)
{
// we MUST avoid duplicates in the "global" list
if ((total & cs.Status) != cs.Status)
{
list.Add(cs);
total |= cs.Status;
}
}
}
// and if required add some
if (flag != X509ChainStatusFlags.NoError)
{
list.Insert(0, new X509ChainStatus(flag));
}
status = (X509ChainStatus[])list.ToArray(typeof(X509ChainStatus));
// (fast path) this ignore everything we have checked
if ((status.Length == 0) || (ChainPolicy.VerificationFlags == X509VerificationFlags.AllFlags))
{
return(true);
}
bool result = true;
// now check if exclude some verification for the "end result" (boolean)
foreach (X509ChainStatus cs in status)
{
switch (cs.Status)
{
case X509ChainStatusFlags.UntrustedRoot:
case X509ChainStatusFlags.PartialChain:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.AllowUnknownCertificateAuthority) != 0);
break;
case X509ChainStatusFlags.NotTimeValid:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeValid) != 0);
break;
// FIXME - from here we needs new test cases for all cases
case X509ChainStatusFlags.NotTimeNested:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreNotTimeNested) != 0);
break;
case X509ChainStatusFlags.InvalidBasicConstraints:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidBasicConstraints) != 0);
break;
case X509ChainStatusFlags.InvalidPolicyConstraints:
case X509ChainStatusFlags.NoIssuanceChainPolicy:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidPolicy) != 0);
break;
case X509ChainStatusFlags.InvalidNameConstraints:
case X509ChainStatusFlags.HasNotSupportedNameConstraint:
case X509ChainStatusFlags.HasNotPermittedNameConstraint:
case X509ChainStatusFlags.HasExcludedNameConstraint:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreInvalidName) != 0);
break;
case X509ChainStatusFlags.InvalidExtension:
// not sure ?!?
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
break;
//
// ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreRootRevocationUnknown) != 0)
// ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreEndRevocationUnknown) != 0)
case X509ChainStatusFlags.CtlNotTimeValid:
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlNotTimeValid) != 0);
break;
case X509ChainStatusFlags.CtlNotSignatureValid:
// ?
break;
// ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreCtlSignerRevocationUnknown) != 0);
case X509ChainStatusFlags.CtlNotValidForUsage:
// FIXME - does IgnoreWrongUsage apply to CTL (it doesn't have Ctl in it's name like the others)
result &= ((ChainPolicy.VerificationFlags & X509VerificationFlags.IgnoreWrongUsage) != 0);
break;
default:
result = false;
break;
}
// once we have one failure there's no need to check further
if (!result)
{
return(false);
}
}
// every "problem" was excluded
return(true);
}
private X509ChainStatusFlags CheckRevocation(BCX509Certificate2 certificate, BCX509Certificate2 ca_cert, bool online)
{
// change this if/when we support OCSP
KeyUsage kue = KeyUsage.GetInstance(ca_cert.CertificateStructure.TbsCertificate.Extensions.GetExtension(X509Extensions.KeyUsage));
if (kue != null)
{
// ... verify CrlSign is set
//KeyUsage success = new KeyUsage(KeyUsage.CrlSign);
if ((kue.IntValue & KeyUsage.CrlSign) != KeyUsage.CrlSign)
{
// FIXME - we should try to find an alternative CA that has the CrlSign bit
return(X509ChainStatusFlags.RevocationStatusUnknown);
}
}
X509Crl crl = FindCrl(ca_cert);
if ((crl == null) && online)
{
// FIXME - download and install new CRL
// then you get a second chance
// crl = FindCrl (ca_cert, ref valid, ref out_of_date);
// We need to get the subjectAltName and an URI from there (or use OCSP)
// X509KeyUsageExtension subjectAltName = (ca_cert.Extensions["2.5.29.17"] as X509KeyUsageExtension);
}
#if !NETCF
if (crl != null)
{
// validate the digital signature on the CRL using the CA public key
// note #1: we can't use X509Crl.VerifySignature(X509Certificate) because it duplicates
// checks and we loose the "why" of the failure
// note #2: we do this before other tests as an invalid signature could be a hacked CRL
// (so anything within can't be trusted)
if (!crl.VerifySignature(ca_cert.GetPublicKey()))
{
return(X509ChainStatusFlags.RevocationStatusUnknown);
}
X509Crl.X509CrlEntry entry = crl.GetCrlEntry(certificate);
if (entry != null)
{
// We have an entry for this CRL that includes an unknown CRITICAL extension
// See [X.509 7.3] NOTE 4
if (!ProcessCrlEntryExtensions(entry))
{
return(X509ChainStatusFlags.Revoked);
}
// FIXME - a little more is involved
if (entry.RevocationDate <= ChainPolicy.VerificationTime)
{
return(X509ChainStatusFlags.Revoked);
}
}
// are we overdue for a CRL update ? if so we can't be sure of any certificate status
if (crl.NextUpdate.Value < ChainPolicy.VerificationTime)
{
return(X509ChainStatusFlags.RevocationStatusUnknown | X509ChainStatusFlags.OfflineRevocation);
}
// we have a CRL that includes an unknown CRITICAL extension
// we put this check at the end so we do not "hide" any Revoked flags
if (!ProcessCrlExtensions(crl))
{
return(X509ChainStatusFlags.RevocationStatusUnknown);
}
}
else
#endif
return(X509ChainStatusFlags.RevocationStatusUnknown);
#if !NETCF
return(X509ChainStatusFlags.NoError);
#endif
}
