Merge GH #454 X.509 name constraints

8 files changed, 630 insertions, 7 deletions

diff --git a/src/lib/cert/x509/cert_status.h b/src/lib/cert/x509/cert_status.h
index 5028af384..6e8635237 100644
--- a/src/lib/cert/x509/cert_status.h
+++ b/src/lib/cert/x509/cert_status.h
@@ -38,6 +38,7 @@ enum class Certificate_Status_Code {
    INVALID_USAGE,
    CERT_CHAIN_TOO_LONG,
    CA_CERT_NOT_FOR_CERT_ISSUER,
+   NAME_CONSTRAINT_ERROR,
 
    // Revocation errors
    CA_CERT_NOT_FOR_CRL_ISSUER,
diff --git a/src/lib/cert/x509/name_constraint.cpp b/src/lib/cert/x509/name_constraint.cpp
new file mode 100644
index 000000000..a1ed19856
--- /dev/null
+++ b/src/lib/cert/x509/name_constraint.cpp
@@ -0,0 +1,273 @@
+/*
+* X.509 Name Constraint
+* (C) 2015 Kai Michaelis
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/name_constraint.h>
+#include <botan/ber_dec.h>
+#include <botan/der_enc.h>
+#include <botan/charset.h>
+#include <botan/loadstor.h>
+#include <botan/x509_dn.h>
+#include <botan/x509cert.h>
+#include <sstream>
+
+namespace Botan {
+
+GeneralName::GeneralName(const std::string& v) : GeneralName()
+   {
+   size_t p = v.find(':');
+
+   if(p != std::string::npos)
+      {
+      m_type = v.substr(0,p);
+      m_name = v.substr(p + 1,std::string::npos);
+      }
+   else
+      {
+      throw Invalid_Argument("Failed to decode Name Constraint");
+      }
+   }
+
+void GeneralName::encode_into(class DER_Encoder&) const
+   {
+   throw Exception("General Name encoding not implemented");
+   }
+
+void GeneralName::decode_from(class BER_Decoder& ber)
+   {
+   BER_Object obj = ber.get_next_object();
+   if((obj.class_tag != CONTEXT_SPECIFIC) &&
+      (obj.class_tag != (CONTEXT_SPECIFIC | CONSTRUCTED)))
+      throw Decoding_Error("Invalid class tag while decoding GeneralName");
+
+   const ASN1_Tag tag = obj.type_tag;
+
+   if(tag == 1 || tag == 2 || tag == 6)
+      {
+      m_name = Charset::transcode(ASN1::to_string(obj),LATIN1_CHARSET,LOCAL_CHARSET);
+
+      if(tag == 1)
+         {
+         m_type = "RFC822";
+         }
+      else if(tag == 2)
+         {
+         m_type = "DNS";
+         }
+      else if(tag == 6)
+         {
+         m_type = "URI";
+         }
+      }
+   else if(tag == 4)
+      {
+      X509_DN dn;
+      std::multimap<std::string, std::string> nam;
+      BER_Decoder dec(obj.value);
+      std::stringstream ss;
+
+      dn.decode_from(dec);
+      ss << dn;
+
+      m_name = ss.str();
+      m_type = "DN";
+      }
+   else if(tag == 7)
+      {
+      if(obj.value.size() == 8)
+         {
+         const std::vector<byte> ip(obj.value.begin(),obj.value.begin() + 4);
+         const std::vector<byte> net(obj.value.begin() + 4,obj.value.end());
+         m_type = "IP";
+         m_name = ipv4_to_string(load_be<u32bit>(ip.data(),0)) + "/" + ipv4_to_string(load_be<u32bit>(net.data(),0));
+         }
+      else if(obj.value.size() == 32)
+         {
+         throw Decoding_Error("Unsupported IPv6 name constraint");
+         }
+      else
+         {
+         throw Decoding_Error("Invalid IP name constraint size " +
+                              std::to_string(obj.value.size()));
+         }
+      }
+   else
+      {
+      throw Decoding_Error("Found unknown GeneralName type");
+      }
+   }
+
+GeneralName::MatchResult GeneralName::matches(const X509_Certificate& cert) const
+   {
+   std::vector<std::string> nam;
+   std::function<bool(const GeneralName*,const std::string&)> match_fn;
+
+   if(type() == "DNS")
+      {
+      match_fn = std::mem_fn(&GeneralName::matches_dns);
+      nam = cert.subject_info("DNS");
+
+      if(nam.empty())
+         {
+         nam = cert.subject_info("CN");
+         }
+      }
+   else if(type() == "DN")
+      {
+      match_fn = std::mem_fn(&GeneralName::matches_dn);
+
+      std::stringstream ss;
+      ss << cert.subject_dn();
+      nam.push_back(ss.str());
+      }
+   else if(type() == "IP")
+      {
+      match_fn = std::mem_fn(&GeneralName::matches_ip);
+      nam = cert.subject_info("IP");
+      }
+   else
+      {
+      return MatchResult::UnknownType;
+      }
+
+   if(nam.empty())
+      {
+      return MatchResult::NotFound;
+      }
+
+   bool some = false;
+   bool all = true;
+
+   for(const std::string& n: nam)
+      {
+      bool m = match_fn(this,n);
+
+      some |= m;
+      all &= m;
+      }
+
+   if(all)
+      {
+      return MatchResult::All;
+      }
+   else if(some)
+      {
+      return MatchResult::Some;
+      }
+   else
+      {
+      return MatchResult::None;
+      }
+   }
+
+bool GeneralName::matches_dns(const std::string& nam) const
+   {
+   if(nam.size() == name().size())
+      {
+      return nam == name();
+      }
+   else if(name().size() > nam.size())
+      {
+      return false;
+      }
+   else // name.size() < nam.size()
+      {
+      std::string constr = name().front() == '.' ? name() : "." + name();
+      // constr is suffix of nam
+      return constr == nam.substr(nam.size() - constr.size(),constr.size());
+      }
+   }
+
+bool GeneralName::matches_dn(const std::string& nam) const
+   {
+   std::stringstream ss(nam);
+   std::stringstream tt(name());
+   X509_DN nam_dn, my_dn;
+
+   ss >> nam_dn;
+   tt >> my_dn;
+
+   auto attr = nam_dn.get_attributes();
+   bool ret = true;
+   int trys = 0;
+
+   for(const std::pair<OID,std::string>& c: my_dn.get_attributes())
+      {
+      auto i = attr.equal_range(c.first);
+
+      if(i.first != i.second)
+         {
+         trys += 1;
+         ret &= i.first->second == c.second;
+         }
+      }
+
+   return trys > 0 && ret;
+   }
+
+bool GeneralName::matches_ip(const std::string& nam) const
+   {
+   u32bit ip = string_to_ipv4(nam);
+   std::vector<std::string> p = split_on(name(),'/');
+
+   if(p.size() != 2)
+      throw Decoding_Error("failed to parse IPv4 address");
+
+   u32bit net = string_to_ipv4(p.at(0));
+   u32bit mask = string_to_ipv4(p.at(1));
+
+   return (ip & mask) == net;
+   }
+
+std::ostream& operator<<(std::ostream& os, const GeneralName& gn)
+   {
+   os << gn.type() << ":" << gn.name();
+   return os;
+   }
+
+GeneralSubtree::GeneralSubtree(const std::string& v) : GeneralSubtree()
+   {
+   size_t p0, p1;
+   size_t min = std::stoull(v, &p0, 10);
+   size_t max = std::stoull(v.substr(p0 + 1), &p1, 10);
+   GeneralName gn(v.substr(p0 + p1 + 2));
+
+   if(p0 > 0 && p1 > 0)
+      {
+      m_minimum = min;
+      m_maximum = max;
+      m_base = gn;
+      }
+   else
+      {
+      throw Invalid_Argument("Failed to decode Name Constraint");
+      }
+   }
+
+void GeneralSubtree::encode_into(class DER_Encoder&) const
+   {
+   throw std::runtime_error("General Subtree encoding not implemented");
+   }
+
+void GeneralSubtree::decode_from(class BER_Decoder& ber)
+   {
+   ber.start_cons(SEQUENCE)
+      .decode(m_base)
+      .decode_optional(m_minimum,ASN1_Tag(0),CONTEXT_SPECIFIC,size_t(0))
+   .end_cons();
+
+   if(m_minimum != 0)
+     throw Decoding_Error("GeneralSubtree minimum must be 0");
+
+   m_maximum = std::numeric_limits<std::size_t>::max();
+   }
+
+std::ostream& operator<<(std::ostream& os, const GeneralSubtree& gs)
+   {
+   os << gs.minimum() << "," << gs.maximum() << "," << gs.base();
+   return os;
+   }
+}
diff --git a/src/lib/cert/x509/name_constraint.h b/src/lib/cert/x509/name_constraint.h
new file mode 100644
index 000000000..345e64ff5
--- /dev/null
+++ b/src/lib/cert/x509/name_constraint.h
@@ -0,0 +1,132 @@
+/*
+* X.509 Name Constraint
+* (C) 2015 Kai Michaelis
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#ifndef BOTAN_NAME_CONSTRAINT_H__
+#define BOTAN_NAME_CONSTRAINT_H__
+
+#include <botan/asn1_obj.h>
+#include <ostream>
+
+namespace Botan {
+
+   class X509_Certificate;
+
+   /**
+    * @brief X.509 GeneralName Type
+    *
+    * Handles parsing GeneralName types in their BER and canonical string
+    * encoding. Allows matching GeneralNames against each other using
+    * the rules laid out in the X.509 4.2.1.10 (Name Contraints).
+    */
+   class BOTAN_DLL GeneralName : public ASN1_Object
+      {
+      public:
+         enum MatchResult : int
+            {
+            All,
+            Some,
+            None,
+            NotFound,
+            UnknownType,
+            };
+
+         GeneralName() : m_type(), m_name() {}
+
+         /// Constructs a new GeneralName for its string format.
+         GeneralName(const std::string& s);
+
+         void encode_into(class DER_Encoder&) const override;
+         void decode_from(class BER_Decoder&) override;
+
+         /// Type of the name. Can be DN, DNS, IP, RFC822, URI.
+         const std::string& type() const { return m_type; }
+
+         /// The name as string. Format depends on type.
+         const std::string& name() const { return m_name; }
+
+         /// Checks whenever a given certificate (partially) matches this name.
+         MatchResult matches(const X509_Certificate&) const;
+
+      private:
+         std::string m_type;
+         std::string m_name;
+
+         bool matches_dns(const std::string&) const;
+         bool matches_dn(const std::string&) const;
+         bool matches_ip(const std::string&) const;
+      };
+
+   std::ostream& operator<<(std::ostream& os, const GeneralName& gn);
+
+   /**
+    * @brief A single Name Constraints
+    *
+    * THe Name Constraint extension adds a minimum and maximum path
+    * length to a GeneralName to form a constraint. The length limits
+    * are currently unused.
+    */
+   class BOTAN_DLL GeneralSubtree : public ASN1_Object
+      {
+      public:
+         GeneralSubtree() : m_base(), m_minimum(0), m_maximum(std::numeric_limits<std::size_t>::max())
+         {}
+
+         /// Constructs a new Name Constraint
+         GeneralSubtree(GeneralName b,size_t min,size_t max)
+         : m_base(b), m_minimum(min), m_maximum(max)
+         {}
+
+         /// Constructs a new GeneralSubtree for its string format.
+         GeneralSubtree(const std::string&);
+
+         void encode_into(class DER_Encoder&) const override;
+         void decode_from(class BER_Decoder&) override;
+
+         /// Name
+         GeneralName base() const { return m_base; }
+
+         // Minimum path length
+         size_t minimum() const { return m_minimum; }
+
+         // Maximum path length
+         size_t maximum() const { return m_maximum; }
+
+      private:
+         GeneralName m_base;
+         size_t m_minimum;
+         size_t m_maximum;
+      };
+
+   std::ostream& operator<<(std::ostream& os, const GeneralSubtree& gs);
+
+   /**
+    * @brief Name Constraints
+    *
+    * Wraps the Name Constraints associated with a certificate.
+    */
+   class BOTAN_DLL NameConstraints
+      {
+      public:
+         NameConstraints() : m_permitted_subtrees(), m_excluded_subtrees() {}
+
+         NameConstraints(std::vector<GeneralSubtree>&& ps, std::vector<GeneralSubtree>&& es)
+         : m_permitted_subtrees(ps), m_excluded_subtrees(es)
+         {}
+
+         /// Permitted names
+         const std::vector<GeneralSubtree>& permitted() const { return m_permitted_subtrees; }
+
+         /// Excluded names
+         const std::vector<GeneralSubtree>& excluded() const { return m_excluded_subtrees; }
+
+      private:
+        std::vector<GeneralSubtree> m_permitted_subtrees;
+        std::vector<GeneralSubtree> m_excluded_subtrees;
+      };
+}
+
+#endif
diff --git a/src/lib/cert/x509/x509_ext.cpp b/src/lib/cert/x509/x509_ext.cpp
index f3a9a7f1c..47fd909eb 100644
--- a/src/lib/cert/x509/x509_ext.cpp
+++ b/src/lib/cert/x509/x509_ext.cpp
@@ -13,6 +13,7 @@
 #include <botan/charset.h>
 #include <botan/internal/bit_ops.h>
 #include <algorithm>
+#include <sstream>
 
 namespace Botan {
 
@@ -32,6 +33,7 @@ Certificate_Extension* Extensions::get_extension(const OID& oid)
    X509_EXTENSION("X509v3.ExtendedKeyUsage", Extended_Key_Usage);
    X509_EXTENSION("X509v3.IssuerAlternativeName", Issuer_Alternative_Name);
    X509_EXTENSION("X509v3.SubjectAlternativeName", Subject_Alternative_Name);
+   X509_EXTENSION("X509v3.NameConstraints", Name_Constraints);
    X509_EXTENSION("X509v3.CertificatePolicies", Certificate_Policies);
    X509_EXTENSION("X509v3.CRLDistributionPoints", CRL_Distribution_Points);
    X509_EXTENSION("PKIX.AuthorityInformationAccess", Authority_Information_Access);
@@ -166,7 +168,10 @@ void Extensions::contents_to(Data_Store& subject_info,
                              Data_Store& issuer_info) const
    {
    for(size_t i = 0; i != m_extensions.size(); ++i)
+      {
       m_extensions[i].first->contents_to(subject_info, issuer_info);
+      subject_info.add(m_extensions[i].first->oid_name() + ".is_critical", (m_extensions[i].second ? 1 : 0));
+      }
    }
 
 
@@ -430,6 +435,71 @@ void Extended_Key_Usage::contents_to(Data_Store& subject, Data_Store&) const
       subject.add("X509v3.ExtendedKeyUsage", m_oids[i].as_string());
    }
 
+/*
+* Encode the extension
+*/
+std::vector<byte> Name_Constraints::encode_inner() const
+   {
+   throw std::runtime_error("Name_Constraints encoding not implemented");
+   }
+
+
+/*
+* Decode the extension
+*/
+void Name_Constraints::decode_inner(const std::vector<byte>& in)
+   {
+   std::vector<GeneralSubtree> permit, exclude;
+   BER_Decoder ber(in);
+   BER_Decoder ext = ber.start_cons(SEQUENCE);
+   BER_Object per = ext.get_next_object();
+
+   ext.push_back(per);
+   if(per.type_tag == 0 && per.class_tag == ASN1_Tag(CONSTRUCTED | CONTEXT_SPECIFIC))
+      {
+      ext.decode_list(permit,ASN1_Tag(0),ASN1_Tag(CONSTRUCTED | CONTEXT_SPECIFIC));
+      if(permit.empty())
+         throw Encoding_Error("Empty Name Contraint list");
+      }
+
+   BER_Object exc = ext.get_next_object();
+   ext.push_back(exc);
+   if(per.type_tag == 1 && per.class_tag == ASN1_Tag(CONSTRUCTED | CONTEXT_SPECIFIC))
+      {
+      ext.decode_list(exclude,ASN1_Tag(1),ASN1_Tag(CONSTRUCTED | CONTEXT_SPECIFIC));
+      if(exclude.empty())
+         throw Encoding_Error("Empty Name Contraint list");
+      }
+
+   ext.end_cons();
+
+   if(permit.empty() && exclude.empty())
+      throw Encoding_Error("Empty Name Contraint extension");
+
+   m_name_constraints = NameConstraints(std::move(permit),std::move(exclude));
+   }
+
+/*
+* Return a textual representation
+*/
+void Name_Constraints::contents_to(Data_Store& subject, Data_Store&) const
+   {
+   std::stringstream ss;
+
+   for(const GeneralSubtree& gs: m_name_constraints.permitted())
+      {
+      ss << gs;
+      subject.add("X509v3.NameConstraints.permitted", ss.str());
+      ss.str(std::string());
+      }
+   for(const GeneralSubtree& gs: m_name_constraints.excluded())
+      {
+      ss << gs;
+      subject.add("X509v3.NameConstraints.excluded", ss.str());
+      ss.str(std::string());
+      }
+   }
+
 namespace {
 
 /*
diff --git a/src/lib/cert/x509/x509_ext.h b/src/lib/cert/x509/x509_ext.h
index 8d2dcb52b..ac456b998 100644
--- a/src/lib/cert/x509/x509_ext.h
+++ b/src/lib/cert/x509/x509_ext.h
@@ -260,6 +260,29 @@ class BOTAN_DLL Extended_Key_Usage final : public Certificate_Extension
    };
 
 /**
+* Name Constraints
+*/
+class BOTAN_DLL Name_Constraints : public Certificate_Extension
+   {
+   public:
+      Name_Constraints* copy() const override
+         { return new Name_Constraints(m_name_constraints); }
+
+      Name_Constraints() {}
+      Name_Constraints(const NameConstraints &nc) : m_name_constraints(nc) {}
+   private:
+      std::string oid_name() const override
+         { return "X509v3.NameConstraints"; }
+
+      bool should_encode() const override { return true; }
+      std::vector<byte> encode_inner() const override;
+      void decode_inner(const std::vector<byte>&) override;
+      void contents_to(Data_Store&, Data_Store&) const override;
+
+      NameConstraints m_name_constraints;
+   };
+
+/**
 * Certificate Policies Extension
 */
 class BOTAN_DLL Certificate_Policies final : public Certificate_Extension
diff --git a/src/lib/cert/x509/x509cert.cpp b/src/lib/cert/x509/x509cert.cpp
index 8d6d9a70a..959cddb53 100644
--- a/src/lib/cert/x509/x509cert.cpp
+++ b/src/lib/cert/x509/x509cert.cpp
@@ -280,6 +280,14 @@ u32bit X509_Certificate::path_limit() const
    }
 
 /*
+* Return if a certificate extension is marked critical
+*/
+bool X509_Certificate::is_critical(const std::string& ex_name) const
+   {
+   return !!m_subject.get1_u32bit(ex_name + ".is_critical",0);
+   }
+
+/*
 * Return the key usage constraints
 */
 Key_Constraints X509_Certificate::constraints() const
@@ -297,6 +305,26 @@ std::vector<std::string> X509_Certificate::ex_constraints() const
    }
 
 /*
+* Return the name constraints
+*/
+NameConstraints X509_Certificate::name_constraints() const
+   {
+   std::vector<GeneralSubtree> permit, exclude;
+
+   for(const std::string& v: m_subject.get("X509v3.NameConstraints.permitted"))
+      {
+      permit.push_back(GeneralSubtree(v));
+      }
+
+   for(const std::string& v: m_subject.get("X509v3.NameConstraints.excluded"))
+      {
+      exclude.push_back(GeneralSubtree(v));
+      }
+
+   return NameConstraints(std::move(permit),std::move(exclude));
+   }
+
+/*
 * Return the list of certificate policies
 */
 std::vector<std::string> X509_Certificate::policies() const
@@ -514,6 +542,33 @@ std::string X509_Certificate::to_string() const
          out << "   " << ex_constraints[i] << "\n";
       }
 
+   NameConstraints name_constraints = this->name_constraints();
+   if(!name_constraints.permitted().empty() ||
+         !name_constraints.excluded().empty())
+      {
+      out << "Name Constraints:\n";
+
+      if(!name_constraints.permitted().empty())
+         {
+         out << "   Permit";
+         for(auto st: name_constraints.permitted())
+            {
+            out << " " << st.base();
+            }
+         out << "\n";
+         }
+
+      if(!name_constraints.excluded().empty())
+         {
+         out << "   Exclude";
+         for(auto st: name_constraints.excluded())
+            {
+            out << " " << st.base();
+            }
+         out << "\n";
+         }
+      }
+
    if(!ocsp_responder().empty())
       out << "OCSP responder " << ocsp_responder() << "\n";
    if(!crl_distribution_point().empty())
diff --git a/src/lib/cert/x509/x509cert.h b/src/lib/cert/x509/x509cert.h
index 32f2bba9f..54d82b1b4 100644
--- a/src/lib/cert/x509/x509cert.h
+++ b/src/lib/cert/x509/x509cert.h
@@ -14,6 +14,7 @@
 #include <botan/asn1_alt_name.h>
 #include <botan/datastor.h>
 #include <botan/key_constraint.h>
+#include <botan/name_constraint.h>
 #include <map>
 
 namespace Botan {
@@ -64,9 +65,9 @@ class BOTAN_DLL X509_Certificate final : public X509_Object
       * "X509.Certificate.start", "X509.Certificate.end",
       * "X509.Certificate.v2.key_id", "X509.Certificate.public_key",
       * "X509v3.BasicConstraints.path_constraint",
-      * "X509v3.BasicConstraints.is_ca", "X509v3.ExtendedKeyUsage",
-      * "X509v3.CertificatePolicies", "X509v3.SubjectKeyIdentifier" or
-      * "X509.Certificate.serial".
+      * "X509v3.BasicConstraints.is_ca", "X509v3.NameConstraints",
+      * "X509v3.ExtendedKeyUsage", "X509v3.CertificatePolicies",
+      * "X509v3.SubjectKeyIdentifier" or "X509.Certificate.serial".
       * @return value(s) of the specified parameter
       */
       std::vector<std::string> subject_info(const std::string& name) const;
@@ -156,6 +157,12 @@ class BOTAN_DLL X509_Certificate final : public X509_Object
       u32bit path_limit() const;
 
       /**
+      * Check whenever a given X509 Extension is marked critical in this
+      * certificate.
+      */
+      bool is_critical(const std::string& ex_name) const;
+
+      /**
       * Get the key constraints as defined in the KeyUsage extension of this
       * certificate.
       * @return key constraints
@@ -164,13 +171,19 @@ class BOTAN_DLL X509_Certificate final : public X509_Object
 
       /**
       * Get the key constraints as defined in the ExtendedKeyUsage
-      * extension of this
-      * certificate.
+      * extension of this certificate.
       * @return key constraints
       */
       std::vector<std::string> ex_constraints() const;
 
       /**
+      * Get the name constraints as defined in the NameConstraints
+      * extension of this certificate.
+      * @return name constraints
+      */
+      NameConstraints name_constraints() const;
+
+      /**
       * Get the policies as defined in the CertificatePolicies extension
       * of this certificate.
       * @return certificate policies
diff --git a/src/lib/cert/x509/x509path.cpp b/src/lib/cert/x509/x509path.cpp
index 71c025280..dd9df6f51 100644
--- a/src/lib/cert/x509/x509path.cpp
+++ b/src/lib/cert/x509/x509path.cpp
@@ -16,8 +16,6 @@
 #include <vector>
 #include <set>
 
-#include <iostream>
-
 namespace Botan {
 
 namespace {
@@ -143,6 +141,62 @@ check_chain(const std::vector<X509_Certificate>& cert_path,
          if(!trusted_hashes.count(subject.hash_used_for_signature()))
             status.insert(Certificate_Status_Code::UNTRUSTED_HASH);
          }
+
+      const NameConstraints& name_constr = issuer.name_constraints();
+
+      if(!name_constr.permitted().empty() || !name_constr.excluded().empty())
+         {
+         if(!issuer.is_CA_cert() || !issuer.is_critical("X509v3.NameConstraints"))
+            cert_status.at(i).insert(Certificate_Status_Code::NAME_CONSTRAINT_ERROR);
+
+         // Check that all subordinate certs pass the name constraint
+         for(size_t j = 0; j <= i; ++j)
+            {
+            if(i == j && at_self_signed_root)
+               continue;
+
+            bool permitted = name_constr.permitted().empty();
+            bool failed = false;
+
+            for(auto c: name_constr.permitted())
+               {
+               switch(c.base().matches(cert_path.at(j)))
+                  {
+                  case GeneralName::MatchResult::NotFound:
+                  case GeneralName::MatchResult::All:
+                     permitted = true;
+                     break;
+                  case GeneralName::MatchResult::UnknownType:
+                     failed = issuer.is_critical("X509v3.NameConstraints");
+                     permitted = true;
+                     break;
+                  default:
+                     break;
+                  }
+               }
+
+            for(auto c: name_constr.excluded())
+               {
+               switch(c.base().matches(cert_path.at(j)))
+                  {
+                  case GeneralName::MatchResult::All:
+                  case GeneralName::MatchResult::Some:
+                     failed = true;
+                     break;
+                  case GeneralName::MatchResult::UnknownType:
+                     failed = issuer.is_critical("X509v3.NameConstraints");
+                     break;
+                  default:
+                     break;
+                  }
+               }
+
+            if(failed || !permitted)
+               {
+               cert_status.at(j).insert(Certificate_Status_Code::NAME_CONSTRAINT_ERROR);
+               }
+            }
+         }
       }
 
    for(size_t i = 0; i != cert_path.size() - 1; ++i)
@@ -416,6 +470,8 @@ const char* Path_Validation_Result::status_string(Certificate_Status_Code code)
          return "OCSP bad status";
       case Certificate_Status_Code::CERT_NAME_NOMATCH:
          return "Certificate does not match provided name";
+      case Certificate_Status_Code::NAME_CONSTRAINT_ERROR:
+         return "Certificate does not pass name constraint";
 
       case Certificate_Status_Code::CERT_IS_REVOKED:
          return "Certificate is revoked";