Add (Extended)KeyUsage KeyUsage, CipherSuite & Protocol to SSL diagno…

…stics (#65634)

This commit extends the SSL diagnostics message to include descriptions of the

- The KeyUsage and ExtendedKeyUsage of the peer's certificate
- The CipherSuite & Protocol (TLS/SSL version) of the current session 

These can be helpful in diagnosing SSL errors.

Co-authored-by: Tim Vernum <tim@adjective.org>

libs/ssl-config/src/main/java/org/elasticsearch/common/ssl/SslDiagnostics.java

@@ -20,11 +20,14 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 
 public class SslDiagnostics {
 
+
     public static List<String> describeValidHostnames(X509Certificate certificate) {
         try {
             final Collection<List<?>> names = certificate.getSubjectAlternativeNames();
@@ -140,6 +143,44 @@ boolean isSameCertificate() {
         }
     }
 
+    /**
+      * These names align with the values (and indices) defined by {@link X509Certificate#getKeyUsage()}
+      */
+    private static final String[] KEY_USAGE_NAMES = new String[] {
+        "digitalSignature",
+        "nonRepudiation",
+        "keyEncipherment",
+        "dataEncipherment",
+        "keyAgreement",
+        "keyCertSign",
+        "cRLSign",
+        "encipherOnly",
+        "decipherOnly" };
+
+    private enum ExtendedKeyUsage {
+        serverAuth ("1.3.6.1.5.5.7.3.1"),
+        clientAuth ("1.3.6.1.5.5.7.3.2"),
+        codeSigning ("1.3.6.1.5.5.7.3.3"),
+        emailProtection ("1.3.6.1.5.5.7.3.4"),
+        timeStamping ("1.3.6.1.5.5.7.3.8"),
+        ocspSigning ("1.3.6.1.5.5.7.3.9");
+
+        private String oid;
+
+        ExtendedKeyUsage(String oid) {
+            this.oid = Objects.requireNonNull(oid);
+        }
+
+        public static String decodeOid(String oid) {
+            for (ExtendedKeyUsage e : values()) {
+                if (e.oid.equals(oid)) {
+                    return e.name();
+                }
+            }
+            return oid;
+        }
+    }
+
     /**
      * @param contextName    The descriptive name of this SSL context (e.g. "xpack.security.transport.ssl")
      * @param trustedIssuers A Map of DN to Certificate, for the issuers that were trusted in the context in which this failure occurred
@@ -166,8 +207,14 @@ public static String getTrustDiagnosticFailure(X509Certificate[] chain, PeerType
             .append(peerType.name().toLowerCase(Locale.ROOT))
             .append(" provided a certificate with subject name [")
             .append(peerCert.getSubjectX500Principal().getName())
-            .append("] and ")
-            .append(fingerprintDescription(peerCert));
+            .append("], ")
+            .append(fingerprintDescription(peerCert))
+            .append(", ")
+            .append(keyUsageDescription(peerCert))
+            .append(" and ")
+            .append(extendedKeyUsageDescription(peerCert));
+
+        addSessionDescription(session, message);
 
         if (peerType == PeerType.SERVER) {
             try {
@@ -395,4 +442,47 @@ private static boolean checkIssuer(X509Certificate certificate, X509Certificate
     private static boolean isSelfIssued(X509Certificate certificate) {
         return certificate.getIssuerX500Principal().equals(certificate.getSubjectX500Principal());
     }
+
+    private static String keyUsageDescription(X509Certificate certificate) {
+        boolean[] keyUsage = certificate.getKeyUsage();
+        if (keyUsage == null || keyUsage.length == 0) {
+            return "no keyUsage";
+        }
+        final String keyUsageDescription = IntStream.range(0, keyUsage.length)
+            .filter(i -> keyUsage[i])
+            .mapToObj(i -> (i < KEY_USAGE_NAMES.length) ? KEY_USAGE_NAMES[i] : ("#" + i))
+            .collect(Collectors.joining(", "));
+        return keyUsageDescription.isEmpty() ? "no keyUsage" : ("keyUsage [" + keyUsageDescription + "]");
+    }
+
+    private static String extendedKeyUsageDescription(X509Certificate certificate) {
+        try {
+            return Optional.ofNullable(certificate.getExtendedKeyUsage())
+                .flatMap(keyUsage -> generateExtendedKeyUsageDescription(keyUsage))
+                .orElse("no extendedKeyUsage");
+        } catch (CertificateParsingException e) {
+            return "invalid extendedKeyUsage [" + e + "]";
+        }
+    }
+
+    private static Optional<String> generateExtendedKeyUsageDescription(List<String> oids) {
+        return oids.stream()
+            .map(ExtendedKeyUsage::decodeOid)
+            .reduce((x, y) -> x + ", " + y)
+            .map(str -> "extendedKeyUsage [" + str + "]");
+    }
+
+    private static void addSessionDescription(SSLSession session, StringBuilder message) {
+        String cipherSuite = Optional.ofNullable(session)
+            .map(SSLSession::getCipherSuite)
+            .orElse("<unknown cipherSuite>");
+        String protocol = Optional.ofNullable(session)
+            .map(SSLSession::getProtocol)
+            .orElse("<unknown protocol>");
+        message.append("; the session uses cipher suite [")
+            .append(cipherSuite)
+            .append("] and protocol [")
+            .append(protocol)
+            .append("]");
+    }
 }