Fix various x509 path validation bugs + path building with ambiguous DNs

Signed-off-by: Fabian Weissberg <[email protected]>

19 files changed, 686 insertions, 49 deletions

diff --git a/src/lib/asn1/oids.cpp b/src/lib/asn1/oids.cpp
index 3e5d02a7b..2c97f1d29 100644
--- a/src/lib/asn1/oids.cpp
+++ b/src/lib/asn1/oids.cpp
@@ -1,7 +1,7 @@
 /*
 * OID maps
 *
-* This file was automatically generated by .\src\scripts\oids.py on 2017-10-19
+* This file was automatically generated by ./src/scripts/oids.py on 2017-12-05
 *
 * All manual edits to this file will be lost. Edit the script
 * then regenerate this source file.
@@ -192,6 +192,7 @@ std::string lookup(const OID& oid)
    if(oid_str == "2.5.29.21") return "X509v3.ReasonCode";
    if(oid_str == "2.5.29.23") return "X509v3.HoldInstructionCode";
    if(oid_str == "2.5.29.24") return "X509v3.InvalidityDate";
+   if(oid_str == "2.5.29.28") return "X509v3.CRLIssuingDistributionPoint";
    if(oid_str == "2.5.29.30") return "X509v3.NameConstraints";
    if(oid_str == "2.5.29.31") return "X509v3.CRLDistributionPoints";
    if(oid_str == "2.5.29.32") return "X509v3.CertificatePolicies";
@@ -364,6 +365,7 @@ OID lookup(const std::string& name)
    if(name == "X509v3.AuthorityKeyIdentifier") return OID("2.5.29.35");
    if(name == "X509v3.BasicConstraints") return OID("2.5.29.19");
    if(name == "X509v3.CRLDistributionPoints") return OID("2.5.29.31");
+   if(name == "X509v3.CRLIssuingDistributionPoint") return OID("2.5.29.28");
    if(name == "X509v3.CRLNumber") return OID("2.5.29.20");
    if(name == "X509v3.CertificatePolicies") return OID("2.5.29.32");
    if(name == "X509v3.ExtendedKeyUsage") return OID("2.5.29.37");
diff --git a/src/lib/x509/asn1_alt_name.cpp b/src/lib/x509/asn1_alt_name.cpp
index 6b3eda917..c9f7c780b 100644
--- a/src/lib/x509/asn1_alt_name.cpp
+++ b/src/lib/x509/asn1_alt_name.cpp
@@ -13,6 +13,9 @@
 #include <botan/internal/stl_util.h>
 #include <botan/parsing.h>
 #include <botan/loadstor.h>
+#include <botan/x509_dn.h>
+
+#include <sstream>
 
 namespace Botan {
 
@@ -131,6 +134,13 @@ void encode_entries(DER_Encoder& encoder,
          store_be(ip, ip_buf);
          encoder.add_object(tagging, CONTEXT_SPECIFIC, ip_buf, 4);
          }
+      else if (type == "DN")
+         {
+         std::stringstream ss(i->second);
+         X509_DN dn;
+         ss >> dn;
+         encoder.encode(dn);
+         }
       }
    }
 
@@ -145,6 +155,7 @@ void AlternativeName::encode_into(DER_Encoder& der) const
 
    encode_entries(der, m_alt_info, "RFC822", ASN1_Tag(1));
    encode_entries(der, m_alt_info, "DNS", ASN1_Tag(2));
+   encode_entries(der, m_alt_info, "DN", ASN1_Tag(4));
    encode_entries(der, m_alt_info, "URI", ASN1_Tag(6));
    encode_entries(der, m_alt_info, "IP", ASN1_Tag(7));
 
@@ -213,6 +224,17 @@ void AlternativeName::decode_from(BER_Decoder& source)
          if(tag == 2) add_attribute("DNS", ASN1::to_string(obj));
          if(tag == 6) add_attribute("URI", ASN1::to_string(obj));
          }
+      else if(tag == 4)
+         {
+         BER_Decoder dec(obj.value);
+         X509_DN dn;
+         std::stringstream ss;
+
+         dec.decode(dn);
+         ss << dn;
+
+         add_attribute("DN", ss.str());
+         }
       else if(tag == 7)
          {
          if(obj.value.size() == 4)
diff --git a/src/lib/x509/cert_status.cpp b/src/lib/x509/cert_status.cpp
index 9561cae57..2c0e74d36 100644
--- a/src/lib/x509/cert_status.cpp
+++ b/src/lib/x509/cert_status.cpp
@@ -22,6 +22,11 @@ const char* to_string(Certificate_Status_Code code)
       case Certificate_Status_Code::VALID_CRL_CHECKED:
          return "Valid CRL examined";
 
+      case Certificate_Status_Code::CERT_SERIAL_NEGATIVE:
+         return "Certificate serial number is negative";
+      case Certificate_Status_Code::DN_TOO_LONG:
+         return "Distinguished name too long";
+
       case Certificate_Status_Code::NO_REVOCATION_DATA:
          return "No revocation data";
       case Certificate_Status_Code::SIGNATURE_METHOD_TOO_WEAK:
@@ -55,6 +60,8 @@ const char* to_string(Certificate_Status_Code code)
 
       case Certificate_Status_Code::POLICY_ERROR:
          return "Certificate policy error";
+      case Certificate_Status_Code::DUPLICATE_CERT_POLICY:
+         return "Certificate contains duplicate policy";
       case Certificate_Status_Code::INVALID_USAGE:
          return "Certificate does not allow the requested usage";
       case Certificate_Status_Code::CERT_CHAIN_TOO_LONG:
@@ -63,6 +70,8 @@ const char* to_string(Certificate_Status_Code code)
          return "CA certificate not allowed to issue certs";
       case Certificate_Status_Code::CA_CERT_NOT_FOR_CRL_ISSUER:
          return "CA certificate not allowed to issue CRLs";
+      case Certificate_Status_Code::NO_MATCHING_CRLDP:
+         return "No CRL with matching distribution point for certificate";
       case Certificate_Status_Code::OCSP_CERT_NOT_LISTED:
          return "OCSP cert not listed";
       case Certificate_Status_Code::OCSP_BAD_STATUS:
@@ -73,6 +82,10 @@ const char* to_string(Certificate_Status_Code code)
          return "Certificate does not pass name constraint";
       case Certificate_Status_Code::UNKNOWN_CRITICAL_EXTENSION:
          return "Unknown critical extension encountered";
+      case Certificate_Status_Code::DUPLICATE_CERT_EXTENSION:
+         return "Duplicate certificate extension encountered";
+      case Certificate_Status_Code::EXT_IN_V1_V2_CERT:
+         return "Encountered extension in certificate with version < 3";
       case Certificate_Status_Code::OCSP_SIGNATURE_ERROR:
          return "OCSP signature error";
       case Certificate_Status_Code::OCSP_ISSUER_NOT_FOUND:
diff --git a/src/lib/x509/cert_status.h b/src/lib/x509/cert_status.h
index 0dd9f7b84..76dc9252b 100644
--- a/src/lib/x509/cert_status.h
+++ b/src/lib/x509/cert_status.h
@@ -25,12 +25,18 @@ enum class Certificate_Status_Code {
    VALID_CRL_CHECKED = 3,
    OCSP_NO_HTTP = 4,
 
+   // Warnings
+   FIRST_WARNING_STATUS = 500,
+   CERT_SERIAL_NEGATIVE = 500,
+   DN_TOO_LONG = 501,
+
    // Errors
    FIRST_ERROR_STATUS = 1000,
 
    SIGNATURE_METHOD_TOO_WEAK = 1000,
    UNTRUSTED_HASH = 1001,
    NO_REVOCATION_DATA = 1002,
+   NO_MATCHING_CRLDP = 1003,
 
    // Time problems
    CERT_NOT_YET_VALID = 2000,
@@ -62,10 +68,13 @@ enum class Certificate_Status_Code {
    // Other problems
    CERT_NAME_NOMATCH = 4008,
    UNKNOWN_CRITICAL_EXTENSION = 4009,
+   DUPLICATE_CERT_EXTENSION = 4010,
    OCSP_SIGNATURE_ERROR = 4501,
    OCSP_ISSUER_NOT_FOUND = 4502,
    OCSP_RESPONSE_MISSING_KEYUSAGE = 4503,
    OCSP_RESPONSE_INVALID = 4504,
+   EXT_IN_V1_V2_CERT = 4505,
+   DUPLICATE_CERT_POLICY = 4506,
 
    // Hard failures
    CERT_IS_REVOKED = 5000,
diff --git a/src/lib/x509/certstor.cpp b/src/lib/x509/certstor.cpp
index df4fc3365..23e8185c4 100644
--- a/src/lib/x509/certstor.cpp
+++ b/src/lib/x509/certstor.cpp
@@ -1,6 +1,7 @@
 /*
 * Certificate Store
 * (C) 1999-2010,2013 Jack Lloyd
+* (C) 2017 Fabian Weissberg, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -64,6 +65,28 @@ Certificate_Store_In_Memory::find_cert(const X509_DN& subject_dn,
    return nullptr;
    }
 
+std::vector<std::shared_ptr<const X509_Certificate>> Certificate_Store_In_Memory::find_all_certs(
+      const X509_DN& subject_dn,
+      const std::vector<uint8_t>& key_id) const
+   {
+   std::vector<std::shared_ptr<const X509_Certificate>> matches;
+
+   for(const auto& cert : m_certs)
+      {
+      if(key_id.size())
+         {
+         std::vector<uint8_t> skid = cert->subject_key_id();
+
+         if(skid.size() && skid != key_id) // no match
+            continue;
+         }
+
+      if(cert->subject_dn() == subject_dn)
+         matches.push_back(cert);
+      }
+
+   return matches;
+   }
 
 std::shared_ptr<const X509_Certificate>
 Certificate_Store_In_Memory::find_cert_by_pubkey_sha1(const std::vector<uint8_t>& key_hash) const
diff --git a/src/lib/x509/certstor.h b/src/lib/x509/certstor.h
index f08e03bae..36d2e4abd 100644
--- a/src/lib/x509/certstor.h
+++ b/src/lib/x509/certstor.h
@@ -31,6 +31,14 @@ class BOTAN_PUBLIC_API(2,0) Certificate_Store
          find_cert(const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const = 0;
 
       /**
+      * Find all certificates with a given Subject DN.
+      * Subject DN and even the key identifier might not be unique.
+      */
+      virtual std::vector<std::shared_ptr<const X509_Certificate>> find_all_certs(
+         const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const = 0;
+
+
+      /**
       * Find a certificate by searching for one with a matching SHA-1 hash of
       * public key. Used for OCSP.
       * @param key_hash SHA-1 hash of the subject's public key
@@ -121,11 +129,19 @@ class BOTAN_PUBLIC_API(2,0) Certificate_Store_In_Memory final : public Certifica
 
       /*
       * Find a certificate by Subject DN and (optionally) key identifier
+      * @return the first certificate that matches
       */
       std::shared_ptr<const X509_Certificate> find_cert(
          const X509_DN& subject_dn,
          const std::vector<uint8_t>& key_id) const override;
 
+      /*
+      * Find all certificates with a given Subject DN.
+      * Subject DN and even the key identifier might not be unique.
+      */
+      std::vector<std::shared_ptr<const X509_Certificate>> find_all_certs(
+         const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const override;
+
       std::shared_ptr<const X509_Certificate>
          find_cert_by_pubkey_sha1(const std::vector<uint8_t>& key_hash) const override;
 
diff --git a/src/lib/x509/certstor_sql/certstor_sql.cpp b/src/lib/x509/certstor_sql/certstor_sql.cpp
index 6acfed060..d2991a019 100644
--- a/src/lib/x509/certstor_sql/certstor_sql.cpp
+++ b/src/lib/x509/certstor_sql/certstor_sql.cpp
@@ -76,6 +76,40 @@ Certificate_Store_In_SQL::find_cert(const X509_DN& subject_dn, const std::vector
    return cert;
    }
 
+std::vector<std::shared_ptr<const X509_Certificate>>
+Certificate_Store_In_SQL::find_all_certs(const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const
+   {
+   std::vector<std::shared_ptr<const X509_Certificate>> certs;
+
+   DER_Encoder enc;
+   std::shared_ptr<SQL_Database::Statement> stmt;
+
+   subject_dn.encode_into(enc);
+
+   if(key_id.empty())
+      {
+      stmt = m_database->new_statement("SELECT certificate FROM " + m_prefix + "certificates WHERE subject_dn == ?1");
+      stmt->bind(1,enc.get_contents_unlocked());
+      }
+   else
+      {
+      stmt = m_database->new_statement("SELECT certificate FROM " + m_prefix + "certificates WHERE\
+                                        subject_dn == ?1 AND (key_id == NULL OR key_id == ?2)");
+      stmt->bind(1,enc.get_contents_unlocked());
+      stmt->bind(2,key_id);
+      }
+
+   std::shared_ptr<const X509_Certificate> cert;
+   while(stmt->step())
+      {
+      auto blob = stmt->get_blob(0);
+      certs.push_back(std::make_shared<X509_Certificate>(
+            std::vector<uint8_t>(blob.first,blob.first + blob.second)));
+      }
+
+   return certs;
+   }
+
 std::shared_ptr<const X509_Certificate>
 Certificate_Store_In_SQL::find_cert_by_pubkey_sha1(const std::vector<uint8_t>& /*key_hash*/) const
    {
@@ -123,9 +157,6 @@ std::vector<X509_DN> Certificate_Store_In_SQL::all_subjects() const
 
 bool Certificate_Store_In_SQL::insert_cert(const X509_Certificate& cert)
    {
-   if(find_cert(cert.subject_dn(),cert.subject_key_id()))
-      return false;
-
    DER_Encoder enc;
    auto stmt = m_database->new_statement("INSERT OR REPLACE INTO " +
                                      m_prefix + "certificates (\
diff --git a/src/lib/x509/certstor_sql/certstor_sql.h b/src/lib/x509/certstor_sql/certstor_sql.h
index 88e3968bf..fd80eb191 100644
--- a/src/lib/x509/certstor_sql/certstor_sql.h
+++ b/src/lib/x509/certstor_sql/certstor_sql.h
@@ -43,6 +43,13 @@ class BOTAN_PUBLIC_API(2,0) Certificate_Store_In_SQL : public Certificate_Store
       std::shared_ptr<const X509_Certificate>
          find_cert(const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const override;
 
+      /*
+      * Find all certificates with a given Subject DN.
+      * Subject DN and even the key identifier might not be unique.
+      */
+      std::vector<std::shared_ptr<const X509_Certificate>> find_all_certs(
+         const X509_DN& subject_dn, const std::vector<uint8_t>& key_id) const override;
+
       std::shared_ptr<const X509_Certificate>
          find_cert_by_pubkey_sha1(const std::vector<uint8_t>& key_hash) const override;
 
diff --git a/src/lib/x509/x509_crl.cpp b/src/lib/x509/x509_crl.cpp
index a739d2f60..c6449baf8 100644
--- a/src/lib/x509/x509_crl.cpp
+++ b/src/lib/x509/x509_crl.cpp
@@ -10,6 +10,8 @@
 #include <botan/x509cert.h>
 #include <botan/ber_dec.h>
 
+#include <sstream>
+
 namespace Botan {
 
 struct CRL_Data
@@ -23,6 +25,7 @@ struct CRL_Data
    // cached values from extensions
    size_t m_crl_number = 0;
    std::vector<uint8_t> m_auth_key_id;
+   std::string m_issuing_distribution_point;
    };
 
 std::string X509_CRL::PEM_label() const
@@ -164,6 +167,26 @@ std::unique_ptr<CRL_Data> decode_crl_body(const std::vector<uint8_t>& body,
 
    tbs_crl.verify_end();
 
+   // Now cache some fields from the extensions
+   if(auto ext = data->m_extensions.get_extension_object_as<Cert_Extension::CRL_Number>())
+      {
+      data->m_crl_number = ext->get_crl_number();
+      }
+   if(auto ext = data->m_extensions.get_extension_object_as<Cert_Extension::Authority_Key_ID>())
+      {
+      data->m_auth_key_id = ext->get_key_id();
+      }
+   if(auto ext = data->m_extensions.get_extension_object_as<Cert_Extension::CRL_Issuing_Distribution_Point>())
+      {
+      std::stringstream ss;
+
+      for(const auto& pair : ext->get_point().contents())
+         {
+         ss << pair.first << ": " << pair.second << " ";
+         }
+      data->m_issuing_distribution_point = ss.str();
+      }
+
    return data;
    }
 
@@ -236,4 +259,11 @@ const X509_Time& X509_CRL::next_update() const
    return data().m_next_update;
    }
 
+/*
+* Return the CRL's distribution point
+*/
+std::string X509_CRL::crl_issuing_distribution_point() const
+   {
+   return data().m_issuing_distribution_point;
+   }
 }
diff --git a/src/lib/x509/x509_crl.h b/src/lib/x509/x509_crl.h
index fb8307d5a..89925aa04 100644
--- a/src/lib/x509/x509_crl.h
+++ b/src/lib/x509/x509_crl.h
@@ -83,6 +83,12 @@ class BOTAN_PUBLIC_API(2,0) X509_CRL final : public X509_Object
       const X509_Time& next_update() const;
 
       /**
+      * Get the CRL's distribution point
+      * @return CRL.IssuingDistributionPoint from the CRL's Data_Store
+      */
+      std::string crl_issuing_distribution_point() const;
+
+      /**
       * Create an uninitialized CRL object. Any attempts to access
       * this object will throw an exception.
       */
diff --git a/src/lib/x509/x509_dn.cpp b/src/lib/x509/x509_dn.cpp
index d07344aae..1561a10f9 100644
--- a/src/lib/x509/x509_dn.cpp
+++ b/src/lib/x509/x509_dn.cpp
@@ -11,6 +11,7 @@
 #include <botan/parsing.h>
 #include <botan/internal/stl_util.h>
 #include <botan/oids.h>
+#include <botan/x509_dn_ub.h>
 #include <ostream>
 #include <cctype>
 
diff --git a/src/lib/x509/x509_dn_ub.cpp b/src/lib/x509/x509_dn_ub.cpp
new file mode 100644
index 000000000..20c88d97e
--- /dev/null
+++ b/src/lib/x509/x509_dn_ub.cpp
@@ -0,0 +1,58 @@
+/*
+* DN_UB maps: Upper bounds on the length of DN strings
+*
+* This file was automatically generated by ./src/scripts/oids.py on 2017-12-20
+*
+* All manual edits to this file will be lost. Edit the script
+* then regenerate this source file.
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/asn1_oid.h>
+#include <botan/x509_dn_ub.h>
+#include <map>
+#include <stdint.h>
+
+namespace {
+/**
+ * Upper bounds for the length of distinguished name fields as given in RFC 5280, Appendix A.
+ * Only OIDS recognized by botan are considered, so far.
+ * Maps OID string representations instead of human readable strings in order
+ * to avoid an additional lookup.
+ */
+static const std::map<Botan::OID, size_t> DN_UB =
+   {
+   { Botan::OID("2.5.4.10"), 64 }, // X520.Organization
+   { Botan::OID("2.5.4.11"), 64 }, // X520.OrganizationalUnit
+   { Botan::OID("2.5.4.12"), 64 }, // X520.Title
+   { Botan::OID("2.5.4.3"), 64 }, // X520.CommonName
+   { Botan::OID("2.5.4.4"), 40 }, // X520.Surname
+   { Botan::OID("2.5.4.42"), 32768 }, // X520.GivenName
+   { Botan::OID("2.5.4.43"), 32768 }, // X520.Initials
+   { Botan::OID("2.5.4.44"), 32768 }, // X520.GenerationalQualifier
+   { Botan::OID("2.5.4.46"), 64 }, // X520.DNQualifier
+   { Botan::OID("2.5.4.5"), 64 }, // X520.SerialNumber
+   { Botan::OID("2.5.4.6"), 3 }, // X520.Country
+   { Botan::OID("2.5.4.65"), 128 }, // X520.Pseudonym
+   { Botan::OID("2.5.4.7"), 128 }, // X520.Locality
+   { Botan::OID("2.5.4.8"), 128 } // X520.State
+   };
+}
+
+namespace Botan {
+
+size_t lookup_ub(const OID& oid)
+   {
+   auto ub_entry = DN_UB.find(oid);
+   if(ub_entry != DN_UB.end())
+      {
+      return ub_entry->second;
+      }
+   else
+      {
+      return SIZE_MAX;
+      }
+   }
+}
+
diff --git a/src/lib/x509/x509_dn_ub.h b/src/lib/x509/x509_dn_ub.h
new file mode 100644
index 000000000..b4433eb53
--- /dev/null
+++ b/src/lib/x509/x509_dn_ub.h
@@ -0,0 +1,24 @@
+/*
+* (C) 2017 Fabian Weissberg, Rohde & Schwarz Cybersecurity
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+#ifndef BOTAN_X509_DN_UB_H_
+#define BOTAN_X509_DN_UB_H_
+
+#include <botan/asn1_oid.h>
+
+namespace Botan {
+
+/**
+* Lookup upper bounds in characters for the length of distinguished name fields
+* as given in RFC 5280, Appendix A.
+*
+* @param oid the oid of the DN to lookup
+* @return the upper bound, or SIZE_MAX if no ub is known to Botan
+*/
+size_t lookup_ub(const OID& oid);
+
+}
+
+#endif
diff --git a/src/lib/x509/x509_ext.cpp b/src/lib/x509/x509_ext.cpp
index 1b13d36e1..d98818a4c 100644
--- a/src/lib/x509/x509_ext.cpp
+++ b/src/lib/x509/x509_ext.cpp
@@ -2,6 +2,7 @@
 * X.509 Certificate Extensions
 * (C) 1999-2010,2012 Jack Lloyd
 * (C) 2016 René Korthaus, Rohde & Schwarz Cybersecurity
+* (C) 2017 Fabian Weissberg, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -15,6 +16,7 @@
 #include <botan/hash.h>
 #include <botan/internal/bit_ops.h>
 #include <algorithm>
+#include <set>
 #include <sstream>
 
 namespace Botan {
@@ -71,6 +73,10 @@ Extensions::create_extn_obj(const OID& oid,
       {
       extn.reset(new Cert_Extension::CRL_Distribution_Points);
       }
+   else if(oid == Cert_Extension::CRL_Issuing_Distribution_Point::static_oid())
+      {
+      extn.reset(new Cert_Extension::CRL_Issuing_Distribution_Point);
+      }
    else if(oid == Cert_Extension::Certificate_Policies::static_oid())
       {
       extn.reset(new Cert_Extension::Certificate_Policies);
@@ -708,7 +714,6 @@ void Certificate_Policies::decode_inner(const std::vector<uint8_t>& in)
    std::vector<Policy_Information> policies;
 
    BER_Decoder(in).decode_list(policies);
-
    m_oids.clear();
    for(size_t i = 0; i != policies.size(); ++i)
       m_oids.push_back(policies[i].oid());
@@ -723,6 +728,18 @@ void Certificate_Policies::contents_to(Data_Store& info, Data_Store&) const
       info.add("X509v3.CertificatePolicies", m_oids[i].as_string());
    }
 
+void Certificate_Policies::validate(const X509_Certificate& subject, const X509_Certificate& issuer,
+            const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
+            std::vector<std::set<Certificate_Status_Code>>& cert_status,
+            size_t pos)
+   {
+   std::set<OID> oid_set(m_oids.begin(), m_oids.end());
+   if(oid_set.size() != m_oids.size())
+      {
+      cert_status.at(pos).insert(Certificate_Status_Code::DUPLICATE_CERT_POLICY);
+      }
+   }
+
 std::vector<uint8_t> Authority_Information_Access::encode_inner() const
    {
    ASN1_String url(m_ocsp_responder, IA5_STRING);
@@ -801,6 +818,7 @@ std::vector<uint8_t> CRL_Number::encode_inner() const
 void CRL_Number::decode_inner(const std::vector<uint8_t>& in)
    {
    BER_Decoder(in).decode(m_crl_number);
+   m_has_value = true;
    }
 
 /*
@@ -850,14 +868,19 @@ void CRL_Distribution_Points::decode_inner(const std::vector<uint8_t>& buf)
       .decode_list(m_distribution_points)
       .verify_end();
 
+   std::stringstream ss;
+
    for(size_t i = 0; i != m_distribution_points.size(); ++i)
       {
-      auto point = m_distribution_points[i].point().contents();
+      auto contents = m_distribution_points[i].point().contents();
 
-      auto uris = point.equal_range("URI");
-      for(auto uri = uris.first; uri != uris.second; ++uri)
-         m_crl_distribution_urls.push_back(uri->second);
+      for(const auto& pair : contents)
+         {
+         ss << pair.first << ": " << pair.second << " ";
+         }
       }
+
+   m_crl_distribution_urls.push_back(ss.str());
    }
 
 void CRL_Distribution_Points::contents_to(Data_Store& subject, Data_Store&) const
@@ -881,6 +904,29 @@ void CRL_Distribution_Points::Distribution_Point::decode_from(class BER_Decoder&
       .end_cons().end_cons();
    }
 
+std::vector<uint8_t> CRL_Issuing_Distribution_Point::encode_inner() const
+   {
+   throw Not_Implemented("CRL_Issuing_Distribution_Point encoding");
+   }
+
+void CRL_Issuing_Distribution_Point::decode_inner(const std::vector<uint8_t>& buf)
+   {
+   BER_Decoder(buf).decode(m_distribution_point).verify_end();
+   }
+
+void CRL_Issuing_Distribution_Point::contents_to(Data_Store& info, Data_Store&) const
+   {
+   auto contents = m_distribution_point.point().contents();
+   std::stringstream ss;
+
+   for(const auto& pair : contents)
+      {
+      ss << pair.first << ": " << pair.second << " ";
+      }
+
+   info.add("X509v3.CRLIssuingDistributionPoint", ss.str());
+   }
+
 std::vector<uint8_t> Unknown_Extension::encode_inner() const
    {
    return m_bytes;
diff --git a/src/lib/x509/x509_ext.h b/src/lib/x509/x509_ext.h
index 1680bd9dd..235496cbd 100644
--- a/src/lib/x509/x509_ext.h
+++ b/src/lib/x509/x509_ext.h
@@ -528,6 +528,10 @@ class BOTAN_PUBLIC_API(2,0) Certificate_Policies final : public Certificate_Exte
       static OID static_oid() { return OID("2.5.29.32"); }
       OID oid_of() const override { return static_oid(); }
 
+      void validate(const X509_Certificate& subject, const X509_Certificate& issuer,
+            const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
+            std::vector<std::set<Certificate_Status_Code>>& cert_status,
+            size_t pos) override;
    private:
       std::string oid_name() const override
          { return "X509v3.CertificatePolicies"; }
@@ -627,6 +631,7 @@ class BOTAN_PUBLIC_API(2,0) CRL_ReasonCode final : public Certificate_Extension
 
 /**
 * CRL Distribution Points Extension
+* todo enforce restrictions from RFC 5280 4.2.1.13
 */
 class BOTAN_PUBLIC_API(2,0) CRL_Distribution_Points final : public Certificate_Extension
    {
@@ -675,6 +680,39 @@ class BOTAN_PUBLIC_API(2,0) CRL_Distribution_Points final : public Certificate_E
    };
 
 /**
+* CRL Issuing Distribution Point Extension
+* todo enforce restrictions from RFC 5280 5.2.5
+*/
+class CRL_Issuing_Distribution_Point final : public Certificate_Extension
+   {
+   public:
+      CRL_Issuing_Distribution_Point() = default;
+
+      explicit CRL_Issuing_Distribution_Point(const CRL_Distribution_Points::Distribution_Point& distribution_point) :
+         m_distribution_point(distribution_point) {}
+
+      CRL_Issuing_Distribution_Point* copy() const override
+         { return new CRL_Issuing_Distribution_Point(m_distribution_point); }
+
+      const AlternativeName& get_point() const
+         { return m_distribution_point.point(); }
+
+      static OID static_oid() { return OID("2.5.29.28"); }
+      OID oid_of() const override { return static_oid(); }
+
+   private:
+      std::string oid_name() const override
+         { return "X509v3.CRLIssuingDistributionPoint"; }
+
+      bool should_encode() const override { return true; }
+      std::vector<uint8_t> encode_inner() const override;
+      void decode_inner(const std::vector<uint8_t>&) override;
+      void contents_to(Data_Store&, Data_Store&) const override;
+
+      CRL_Distribution_Points::Distribution_Point m_distribution_point;
+   };
+
+/**
 * An unknown X.509 extension
 * Will add a failure to the path validation result, if critical
 */
diff --git a/src/lib/x509/x509cert.cpp b/src/lib/x509/x509cert.cpp
index b1229679c..5a5521e37 100644
--- a/src/lib/x509/x509cert.cpp
+++ b/src/lib/x509/x509cert.cpp
@@ -25,6 +25,7 @@ struct X509_Certificate_Data
    {
    size_t m_version = 0;
    std::vector<uint8_t> m_serial;
+   bool m_serial_negative;
    AlgorithmIdentifier m_sig_algo_inner;
    X509_DN m_issuer_dn;
    X509_DN m_subject_dn;
@@ -113,6 +114,8 @@ std::unique_ptr<X509_Certificate_Data> parse_x509_cert_body(const X509_Object& o
       throw Decoding_Error("Unknown X.509 cert version " + std::to_string(data->m_version));
    if(obj.signature_algorithm() != data->m_sig_algo_inner)
       throw Decoding_Error("X.509 Certificate had differing algorithm identifers in inner and outer ID fields");
+   // crude method to save the serial's sign; will get lost during decoding, otherwise
+   data->m_serial_negative = serial_bn.is_negative();
 
    // for general sanity convert wire version (0 based) to standards version (v1 .. v3)
    data->m_version += 1;
@@ -384,6 +387,12 @@ const std::vector<uint8_t>& X509_Certificate::serial_number() const
    return data().m_serial;
    }
 
+bool X509_Certificate::is_serial_negative() const
+   {
+   return data().m_serial_negative;
+   }
+
+
 const X509_DN& X509_Certificate::issuer_dn() const
    {
    return data().m_issuer_dn;
diff --git a/src/lib/x509/x509cert.h b/src/lib/x509/x509cert.h
index dc32e70c1..9ee3d4eb8 100644
--- a/src/lib/x509/x509cert.h
+++ b/src/lib/x509/x509cert.h
@@ -186,6 +186,12 @@ class BOTAN_PUBLIC_API(2,0) X509_Certificate : public X509_Object
       const std::vector<uint8_t>& serial_number() const;
 
       /**
+      * Get the serial number's sign
+      * @return 1 iff the serial is negative.
+      */
+      bool is_serial_negative() const;
+
+      /**
       * Get the DER encoded AuthorityKeyIdentifier of this certificate.
       * @return DER encoded AuthorityKeyIdentifier
       */
diff --git a/src/lib/x509/x509path.cpp b/src/lib/x509/x509path.cpp
index c2a22e7f4..88fd578b2 100644
--- a/src/lib/x509/x509path.cpp
+++ b/src/lib/x509/x509path.cpp
@@ -1,18 +1,23 @@
 /*
 * X.509 Certificate Path Validation
 * (C) 2010,2011,2012,2014,2016 Jack Lloyd
+* (C) 2017 Fabian Weissberg, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
 
 #include <botan/x509path.h>
 #include <botan/x509_ext.h>
+#include <botan/x509_dn_ub.h>
 #include <botan/pk_keys.h>
 #include <botan/ocsp.h>
+#include <botan/oids.h>
 #include <algorithm>
 #include <chrono>
 #include <vector>
 #include <set>
+#include <string>
+#include <sstream>
 
 #if defined(BOTAN_HAS_ONLINE_REVOCATION_CHECKS)
   #include <future>
@@ -81,6 +86,22 @@ PKIX::check_chain(const std::vector<std::shared_ptr<const X509_Certificate>>& ce
          status.insert(Certificate_Status_Code::CHAIN_NAME_MISMATCH);
          }
 
+      // Check the serial number
+      if(subject->is_serial_negative())
+         {
+         status.insert(Certificate_Status_Code::CERT_SERIAL_NEGATIVE);
+         }
+
+      // Check the subject's DN components' length
+      for(const auto& dn_pair : subject->subject_dn().get_attributes())
+         {
+         // dn_pair = <OID,str>
+         if(lookup_ub(dn_pair.first) < dn_pair.second.size())
+            {
+            status.insert(Certificate_Status_Code::DN_TOO_LONG);
+            }
+         }
+
       // Check all certs for valid time range
       if(validation_time < subject->not_before())
          status.insert(Certificate_Status_Code::CERT_NOT_YET_VALID);
@@ -94,34 +115,52 @@ PKIX::check_chain(const std::vector<std::shared_ptr<const X509_Certificate>>& ce
 
       std::unique_ptr<Public_Key> issuer_key(issuer->subject_public_key());
 
-      if(!issuer_key)
+      // Check the signature algorithm
+      if(OIDS::lookup(subject->signature_algorithm().oid).empty())
          {
-         status.insert(Certificate_Status_Code::CERT_PUBKEY_INVALID);
+         status.insert(Certificate_Status_Code::SIGNATURE_ALGO_UNKNOWN);
          }
+      // only perform the following checks if the signature algorithm is known
       else
          {
-         const Certificate_Status_Code sig_status = subject->verify_signature(*issuer_key);
+         if(!issuer_key)
+            {
+            status.insert(Certificate_Status_Code::CERT_PUBKEY_INVALID);
+            }
+         else
+            {
+            const Certificate_Status_Code sig_status = subject->verify_signature(*issuer_key);
 
-         if(sig_status != Certificate_Status_Code::VERIFIED)
-            status.insert(sig_status);
+            if(sig_status != Certificate_Status_Code::VERIFIED)
+               status.insert(sig_status);
 
-         if(issuer_key->estimated_strength() < min_signature_algo_strength)
-            status.insert(Certificate_Status_Code::SIGNATURE_METHOD_TOO_WEAK);
-         }
+            if(issuer_key->estimated_strength() < min_signature_algo_strength)
+               status.insert(Certificate_Status_Code::SIGNATURE_METHOD_TOO_WEAK);
+            }
 
-      // Ignore untrusted hashes on self-signed roots
-      if(trusted_hashes.size() > 0 && !at_self_signed_root)
-         {
-         if(trusted_hashes.count(subject->hash_used_for_signature()) == 0)
-            status.insert(Certificate_Status_Code::UNTRUSTED_HASH);
+         // Ignore untrusted hashes on self-signed roots
+         if(trusted_hashes.size() > 0 && !at_self_signed_root)
+            {
+            if(trusted_hashes.count(subject->hash_used_for_signature()) == 0)
+               status.insert(Certificate_Status_Code::UNTRUSTED_HASH);
+            }
          }
 
       // Check cert extensions
       Extensions extensions = subject->v3_extensions();
-      for(auto& extension : extensions.extensions())
+      const auto& extensions_vec = extensions.extensions();
+      if(subject->x509_version() < 3 && !extensions_vec.empty())
+         {
+         status.insert(Certificate_Status_Code::EXT_IN_V1_V2_CERT);
+         }
+      for(auto& extension : extensions_vec)
          {
          extension.first->validate(*subject, *issuer, cert_path, cert_status, i);
          }
+      if(extensions.extensions().size() != extensions.get_extension_oids().size())
+         {
+         status.insert(Certificate_Status_Code::DUPLICATE_CERT_EXTENSION);
+         }
       }
 
    // path len check
@@ -245,6 +284,28 @@ PKIX::check_crl(const std::vector<std::shared_ptr<const X509_Certificate>>& cert
 
          if(crls[i]->is_revoked(*subject))
             status.insert(Certificate_Status_Code::CERT_IS_REVOKED);
+
+         std::string dp = subject->crl_distribution_point();
+         if(!dp.empty())
+            {
+            if(dp != crls[i]->crl_issuing_distribution_point())
+               {
+               status.insert(Certificate_Status_Code::NO_MATCHING_CRLDP);
+               }
+            }
+
+         for(const auto& extension : crls[i]->extensions().extensions())
+            {
+            // is the extension critical and unknown?
+            if(extension.second && OIDS::lookup(extension.first->oid_of()) == "")
+               {
+               /* NIST Certificate Path Valiadation Testing document: "When an implementation does not recognize a critical extension in the
+                * crlExtensions field, it shall assume that identified certificates have been revoked and are no longer valid"
+                */
+               status.insert(Certificate_Status_Code::CERT_IS_REVOKED);
+               }
+            }
+
          }
       }
 
@@ -514,6 +575,176 @@ PKIX::build_certificate_path(std::vector<std::shared_ptr<const X509_Certificate>
       }
    }
 
+/**
+ * utilities for PKIX::build_all_certificate_paths
+ */
+namespace
+{
+// <certificate, trusted?>
+using cert_maybe_trusted = std::pair<std::shared_ptr<const X509_Certificate>,bool>;
+}
+
+/**
+ * Build all possible certificate paths from the end certificate to self-signed trusted roots.
+ *
+ * All potentially valid paths are put into the cert_paths vector. If no potentially valid paths are found,
+ * one of the encountered errors is returned arbitrarily.
+ *
+ * todo add a path building function that returns detailed information on errors encountered while building
+ * the potentially numerous path candidates.
+ *
+ * Basically, a DFS is performed starting from the end certificate. A stack (vector) serves to control the DFS.
+ * At the beginning of each iteration, a pair is popped from the stack that contains (1) the next certificate
+ * to add to the path (2) a bool that indicates if the certificate is part of a trusted certstore. Ideally, we
+ * follow the unique issuer of the current certificate until a trusted root is reached. However, the issuer DN +
+ * authority key id need not be unique among the certificates used for building the path. In such a case,
+ * we consider all the matching issuers by pushing <IssuerCert, trusted?> on the stack for each of them.
+ *
+ */
+Certificate_Status_Code
+PKIX::build_all_certificate_paths(std::vector<std::vector<std::shared_ptr<const X509_Certificate>>>& cert_paths_out,
+                                  const std::vector<Certificate_Store*>& trusted_certstores,
+                                  const std::shared_ptr<const X509_Certificate>& end_entity,
+                                  const std::vector<std::shared_ptr<const X509_Certificate>>& end_entity_extra)
+   {
+   if(!cert_paths_out.empty())
+      {
+      throw Invalid_Argument("PKIX::build_all_certificate_paths: cert_paths_out must be empty");
+      }
+
+   if(end_entity->is_self_signed())
+      {
+      return Certificate_Status_Code::CANNOT_ESTABLISH_TRUST;
+      }
+
+   /*
+    * Pile up error messages
+    */
+   std::vector<Certificate_Status_Code> stats;
+
+   Certificate_Store_In_Memory ee_extras;
+   for(size_t i = 0; i != end_entity_extra.size(); ++i)
+      {
+      ee_extras.add_certificate(end_entity_extra[i]);
+      }
+
+   /*
+   * This is an inelegant but functional way of preventing path loops
+   * (where C1 -> C2 -> C3 -> C1). We store a set of all the certificate
+   * fingerprints in the path. If there is a duplicate, we error out.
+   * TODO: save fingerprints in result struct? Maybe useful for blacklists, etc.
+   */
+   std::set<std::string> certs_seen;
+
+   // new certs are added and removed from the path during the DFS
+   // it is copied into cert_paths_out when we encounter a trusted root
+   std::vector<std::shared_ptr<const X509_Certificate>> path_so_far;
+
+   // todo can we assume that the end certificate is not trusted?
+   std::vector<cert_maybe_trusted> stack = { {end_entity, false} };
+
+   while(!stack.empty())
+      {
+      // found a deletion marker that guides the DFS, backtracing
+      if(stack.back().first == nullptr)
+         {
+         stack.pop_back();
+         std::string fprint = path_so_far.back()->fingerprint("SHA-256");
+         certs_seen.erase(fprint);
+         path_so_far.pop_back();
+         }
+      // process next cert on the path
+      else
+         {
+         std::shared_ptr<const X509_Certificate> last = stack.back().first;
+         bool trusted = stack.back().second;
+         stack.pop_back();
+
+         // certificate already seen?
+         const std::string fprint = last->fingerprint("SHA-256");
+         if(certs_seen.count(fprint) == 1)
+            {
+            stats.push_back(Certificate_Status_Code::CERT_CHAIN_LOOP);
+            // the current path ended in a loop
+            continue;
+            }
+
+         // the current path ends here
+         if(last->is_self_signed())
+            {
+            // found a trust anchor
+            if(trusted)
+               {
+               cert_paths_out.push_back(path_so_far);
+               cert_paths_out.back().push_back(last);
+
+               continue;
+               }
+            // found an untrustworthy root
+            else
+               {
+               stats.push_back(Certificate_Status_Code::CANNOT_ESTABLISH_TRUST);
+               continue;
+               }
+            }
+
+         const X509_DN issuer_dn = last->issuer_dn();
+         const std::vector<uint8_t> auth_key_id = last->authority_key_id();
+
+         // search for trusted issuers
+         std::vector<std::shared_ptr<const X509_Certificate>> trusted_issuers;
+         for(Certificate_Store* store : trusted_certstores)
+            {
+            auto new_issuers = store->find_all_certs(issuer_dn, auth_key_id);
+            trusted_issuers.insert(trusted_issuers.end(), new_issuers.begin(), new_issuers.end());
+            }
+
+         // search the supplemental certs
+         std::vector<std::shared_ptr<const X509_Certificate>> misc_issuers =
+            ee_extras.find_all_certs(issuer_dn, auth_key_id);
+
+         // if we could not find any issuers, the current path ends here
+         if(trusted_issuers.size() + misc_issuers.size() == 0)
+            {
+            stats.push_back(Certificate_Status_Code::CERT_ISSUER_NOT_FOUND);
+            continue;
+            }
+
+         // push the latest certificate onto the path_so_far
+         path_so_far.push_back(last);
+         certs_seen.emplace(fprint);
+
+         // push a deletion marker on the stack for backtracing later
+         stack.push_back({std::shared_ptr<const X509_Certificate>(nullptr),false});
+
+         for(const auto trusted : trusted_issuers)
+            {
+            stack.push_back({trusted,true});
+            }
+
+         for(const auto misc : misc_issuers)
+            {
+            stack.push_back({misc,false});
+            }
+         }
+      }
+
+   // could not construct any potentially valid path
+   if(cert_paths_out.empty())
+      {
+      if(stats.empty())
+         throw Exception("X509 path building failed for unknown reasons");
+      else
+         // arbitrarily return the first error
+         return stats[0];
+      }
+   else
+      {
+      return Certificate_Status_Code::OK;
+      }
+   }
+
+
 void PKIX::merge_revocation_status(CertificatePathStatusCodes& chain_status,
                                    const CertificatePathStatusCodes& crl,
                                    const CertificatePathStatusCodes& ocsp,
@@ -597,7 +828,9 @@ Path_Validation_Result x509_path_validate(
    const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_resp)
    {
    if(end_certs.empty())
+      {
       throw Invalid_Argument("x509_path_validate called with no subjects");
+      }
 
    std::shared_ptr<const X509_Certificate> end_entity(std::make_shared<const X509_Certificate>(end_certs[0]));
    std::vector<std::shared_ptr<const X509_Certificate>> end_entity_extra;
@@ -606,9 +839,8 @@ Path_Validation_Result x509_path_validate(
       end_entity_extra.push_back(std::make_shared<const X509_Certificate>(end_certs[i]));
       }
 
-   std::vector<std::shared_ptr<const X509_Certificate>> cert_path;
-   Certificate_Status_Code path_building_result =
-      PKIX::build_certificate_path(cert_path, trusted_roots, end_entity, end_entity_extra);
+   std::vector<std::vector<std::shared_ptr<const X509_Certificate>>> cert_paths;
+   Certificate_Status_Code path_building_result = PKIX::build_all_certificate_paths(cert_paths, trusted_roots, end_entity, end_entity_extra);
 
    // If we cannot successfully build a chain to a trusted self-signed root, stop now
    if(path_building_result != Certificate_Status_Code::OK)
@@ -616,38 +848,52 @@ Path_Validation_Result x509_path_validate(
       return Path_Validation_Result(path_building_result);
       }
 
-   CertificatePathStatusCodes status =
-      PKIX::check_chain(cert_path, ref_time,
-                        hostname, usage,
-                        restrictions.minimum_key_strength(),
-                        restrictions.trusted_hashes());
+   std::vector<Path_Validation_Result> error_results;
+   // Try validating all the potentially valid paths and return the first one to validate properly
+   for(auto cert_path : cert_paths)
+      {
+      CertificatePathStatusCodes status =
+         PKIX::check_chain(cert_path, ref_time,
+                           hostname, usage,
+                           restrictions.minimum_key_strength(),
+                           restrictions.trusted_hashes());
 
-   CertificatePathStatusCodes crl_status =
-      PKIX::check_crl(cert_path, trusted_roots, ref_time);
+      CertificatePathStatusCodes crl_status =
+         PKIX::check_crl(cert_path, trusted_roots, ref_time);
 
-   CertificatePathStatusCodes ocsp_status;
+      CertificatePathStatusCodes ocsp_status;
 
-   if(ocsp_resp.size() > 0)
-      {
-      ocsp_status = PKIX::check_ocsp(cert_path, ocsp_resp, trusted_roots, ref_time);
-      }
+      if(ocsp_resp.size() > 0)
+         {
+         ocsp_status = PKIX::check_ocsp(cert_path, ocsp_resp, trusted_roots, ref_time);
+         }
 
-   if(ocsp_status.empty() && ocsp_timeout != std::chrono::milliseconds(0))
-      {
+      if(ocsp_status.empty() && ocsp_timeout != std::chrono::milliseconds(0))
+         {
 #if defined(BOTAN_TARGET_OS_HAS_THREADS) && defined(BOTAN_HAS_HTTP_UTIL)
-      ocsp_status = PKIX::check_ocsp_online(cert_path, trusted_roots, ref_time,
-                                            ocsp_timeout, restrictions.ocsp_all_intermediates());
+         ocsp_status = PKIX::check_ocsp_online(cert_path, trusted_roots, ref_time,
+                                               ocsp_timeout, restrictions.ocsp_all_intermediates());
 #else
-      ocsp_status.resize(1);
-      ocsp_status[0].insert(Certificate_Status_Code::OCSP_NO_HTTP);
+         ocsp_status.resize(1);
+         ocsp_status[0].insert(Certificate_Status_Code::OCSP_NO_HTTP);
 #endif
-      }
+         }
 
-   PKIX::merge_revocation_status(status, crl_status, ocsp_status,
-                                 restrictions.require_revocation_information(),
-                                 restrictions.ocsp_all_intermediates());
+      PKIX::merge_revocation_status(status, crl_status, ocsp_status,
+                                    restrictions.require_revocation_information(),
+                                    restrictions.ocsp_all_intermediates());
 
-   return Path_Validation_Result(status, std::move(cert_path));
+      Path_Validation_Result pvd(status, std::move(cert_path));
+      if(pvd.successful_validation())
+         {
+         return pvd;
+         }
+      else
+         {
+         error_results.push_back(std::move(pvd));
+         }
+      }
+   return error_results[0];
    }
 
 Path_Validation_Result x509_path_validate(
@@ -716,9 +962,31 @@ Path_Validation_Restrictions::Path_Validation_Restrictions(bool require_rev,
    m_trusted_hashes.insert("SHA-512");
    }
 
+namespace {
+CertificatePathStatusCodes find_warnings(const CertificatePathStatusCodes& all_statuses)
+   {
+   CertificatePathStatusCodes warnings;
+   for(const auto& status_set_i : all_statuses)
+      {
+      std::set<Certificate_Status_Code> warning_set_i;
+      for(const auto& code : status_set_i)
+         {
+         if(code >= Certificate_Status_Code::FIRST_WARNING_STATUS &&
+            code < Certificate_Status_Code::FIRST_ERROR_STATUS)
+            {
+            warning_set_i.insert(code);
+            }
+         }
+      warnings.push_back(warning_set_i);
+      }
+   return warnings;
+   }
+}
+
 Path_Validation_Result::Path_Validation_Result(CertificatePathStatusCodes status,
                                                std::vector<std::shared_ptr<const X509_Certificate>>&& cert_chain) :
    m_all_status(status),
+   m_warnings(find_warnings(m_all_status)),
    m_cert_path(cert_chain),
    m_overall(PKIX::overall_status(m_all_status))
    {
@@ -749,6 +1017,16 @@ bool Path_Validation_Result::successful_validation() const
            result() == Certificate_Status_Code::VALID_CRL_CHECKED);
    }
 
+bool Path_Validation_Result::no_warnings() const
+   {
+   return m_warnings.empty();
+   }
+
+CertificatePathStatusCodes Path_Validation_Result::warnings() const
+   {
+   return m_warnings;
+   }
+
 std::string Path_Validation_Result::result_string() const
    {
    return status_string(result());
diff --git a/src/lib/x509/x509path.h b/src/lib/x509/x509path.h
index 6898d0679..12a924873 100644
--- a/src/lib/x509/x509path.h
+++ b/src/lib/x509/x509path.h
@@ -136,6 +136,11 @@ class BOTAN_PUBLIC_API(2,0) Path_Validation_Result final
       bool successful_validation() const;
 
       /**
+      * @return true iff no warnings occured during validation
+      */
+      bool no_warnings() const;
+
+      /**
       * @return overall validation result code
       */
       Certificate_Status_Code result() const { return m_overall; }
@@ -147,6 +152,11 @@ class BOTAN_PUBLIC_API(2,0) Path_Validation_Result final
          { return m_all_status; }
 
       /**
+      * @return the subset of status codes that are warnings
+      */
+      CertificatePathStatusCodes warnings() const;
+
+      /**
       * @return string representation of the validation result
       */
       std::string result_string() const;
@@ -173,6 +183,7 @@ class BOTAN_PUBLIC_API(2,0) Path_Validation_Result final
 
    private:
       CertificatePathStatusCodes m_all_status;
+      CertificatePathStatusCodes m_warnings;
       std::vector<std::shared_ptr<const X509_Certificate>> m_cert_path;
       Certificate_Status_Code m_overall;
    };
@@ -274,6 +285,13 @@ Path_Validation_Result BOTAN_PUBLIC_API(2,0) x509_path_validate(
 */
 namespace PKIX {
 
+Certificate_Status_Code
+build_all_certificate_paths(std::vector<std::vector<std::shared_ptr<const X509_Certificate>>>& cert_paths,
+                            const std::vector<Certificate_Store*>& trusted_certstores,
+                            const std::shared_ptr<const X509_Certificate>& end_entity,
+                            const std::vector<std::shared_ptr<const X509_Certificate>>& end_entity_extra);
+
+
 /**
 * Build certificate path
 * @param cert_path_out output parameter, cert_path will be appended to this vector