Add some new helpers to Certificates

sigstore-java/src/main/java/dev/sigstore/encryption/certificates/Certificates.java

@@ -26,10 +26,13 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
 import org.bouncycastle.openssl.jcajce.JcaPEMWriter;
 
 public class Certificates {
 
+  private static final String SCT_X509_OID = "1.3.6.1.4.1.11129.2.4.2";
+
   /** Convert a certificate to a PEM encoded certificate. */
   public static String toPemString(Certificate cert) throws IOException {
     var certWriter = new StringWriter();
@@ -137,15 +140,69 @@ public static CertPath toCertPath(Certificate certificate) throws CertificateExc
     return cf.generateCertPath(Collections.singletonList(certificate));
   }
 
-  /** Appends an X509Certificate to a {@link CertPath} as a leaf. */
-  public static CertPath appendCertPath(CertPath root, Certificate certificate)
+  /** Appends a CertPath to another {@link CertPath} as children. */
+  public static CertPath appendCertPath(CertPath parent, Certificate child)
       throws CertificateException {
     CertificateFactory cf = CertificateFactory.getInstance("X.509");
     List<Certificate> certs =
-        ImmutableList.<Certificate>builder()
-            .add(certificate)
-            .addAll(root.getCertificates())
-            .build();
+        ImmutableList.<Certificate>builder().add(child).addAll(parent.getCertificates()).build();
     return cf.generateCertPath(certs);
   }
+
+  /**
+   * Trims a parent CertPath from a provided CertPath. This is intended to be used to trim trusted
+   * root and intermediates from a full CertPath to reveal just the untrusted parts which can be
+   * distributed as part of a signature tuple or bundle.
+   *
+   * @param certPath a certificate path to trim from
+   * @param parentPath the parent certPath to trim off the full certPath
+   * @return a trimmed path
+   * @throws IllegalArgumentException if the trimPath is not a parent of the certPath or if they are
+   *     the same length
+   * @throws CertificateException if an error occurs during CertPath construction
+   */
+  public static CertPath trimParent(CertPath certPath, CertPath parentPath)
+      throws CertificateException {
+    if (!containsParent(certPath, parentPath)) {
+      throw new IllegalArgumentException("trim path was not the parent of the provider chain");
+    }
+    var certs = certPath.getCertificates();
+    var parent = parentPath.getCertificates();
+    CertificateFactory cf = CertificateFactory.getInstance("X.509");
+    return cf.generateCertPath(certs.subList(0, certs.size() - parent.size()));
+  }
+
+  /** Check if a parent certpath is the suffix of a certpath */
+  public static boolean containsParent(CertPath certPath, CertPath parentPath) {
+    var certs = certPath.getCertificates();
+    var parent = parentPath.getCertificates();
+    return parent.size() <= certs.size()
+        && certs.subList(certs.size() - parent.size(), certs.size()).equals(parent);
+  }
+
+  /**
+   * Find and return any SCTs embedded in a certificate.
+   *
+   * @param certificate the certificate with embedded scts
+   * @return a byte array containing any number of embedded scts
+   */
+  public static Optional<byte[]> getEmbeddedSCTs(Certificate certificate) {
+    return Optional.ofNullable(((X509Certificate) certificate).getExtensionValue(SCT_X509_OID));
+  }
+
+  /** Check if a certificate is self-signed. */
+  public static boolean isSelfSigned(Certificate certificate) {
+    return ((X509Certificate) certificate)
+        .getIssuerX500Principal()
+        .equals(((X509Certificate) certificate).getSubjectX500Principal());
+  }
+
+  /** Check if the root of a CertPath is self-signed */
+  public static boolean isSelfSigned(CertPath certPath) {
+    return isSelfSigned(certPath.getCertificates().get(certPath.getCertificates().size() - 1));
+  }
+
+  public static X509Certificate getLeaf(CertPath certPath) {
+    return (X509Certificate) certPath.getCertificates().get(0);
+  }
 }

sigstore-java/src/test/java/dev/sigstore/encryption/certificates/CertificatesTest.java

@@ -19,6 +19,7 @@
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.security.cert.CertificateException;
+import java.security.cert.CertificateFactory;
 import java.util.ArrayList;
 import java.util.List;
 import org.bouncycastle.util.encoders.Base64;
@@ -134,16 +135,55 @@ public void toCertPath() throws Exception {
 
   @Test
   public void appendCertPath() throws Exception {
-    var certPath =
+    var parent =
         Certificates.fromPemChain(Resources.toByteArray(Resources.getResource(CERT_CHAIN)));
-    var cert = Certificates.fromPem(Resources.toByteArray(Resources.getResource(CERT_GH)));
+    var child = Certificates.fromPem(Resources.toByteArray(Resources.getResource(CERT_GH)));
 
-    Assertions.assertEquals(2, certPath.getCertificates().size());
-    var appended = Certificates.appendCertPath(certPath, cert);
+    Assertions.assertEquals(2, parent.getCertificates().size());
+    var appended = Certificates.appendCertPath(parent, child);
 
     Assertions.assertEquals(3, appended.getCertificates().size());
-    Assertions.assertEquals(cert, appended.getCertificates().get(0));
-    Assertions.assertEquals(certPath.getCertificates().get(0), appended.getCertificates().get(1));
-    Assertions.assertEquals(certPath.getCertificates().get(1), appended.getCertificates().get(2));
+    Assertions.assertEquals(child, appended.getCertificates().get(0));
+    Assertions.assertEquals(parent.getCertificates().get(0), appended.getCertificates().get(1));
+    Assertions.assertEquals(parent.getCertificates().get(1), appended.getCertificates().get(2));
+  }
+
+  @Test
+  public void trimParent() throws Exception {
+    var certPath =
+        Certificates.fromPemChain(Resources.toByteArray(Resources.getResource(CERT_CHAIN)));
+    var parent =
+        CertificateFactory.getInstance("X.509")
+            .generateCertPath(List.of(certPath.getCertificates().get(1)));
+
+    var trimmed = Certificates.trimParent(certPath, parent);
+
+    Assertions.assertEquals(1, trimmed.getCertificates().size());
+    Assertions.assertEquals(certPath.getCertificates().get(0), trimmed.getCertificates().get(0));
+  }
+
+  @Test
+  public void containsParent() throws Exception {
+    var certPath =
+        Certificates.fromPemChain(Resources.toByteArray(Resources.getResource(CERT_CHAIN)));
+    var parent =
+        CertificateFactory.getInstance("X.509")
+            .generateCertPath(List.of(certPath.getCertificates().get(1)));
+    var cert = Certificates.fromPemChain(Resources.toByteArray(Resources.getResource(CERT)));
+
+    Assertions.assertTrue(Certificates.containsParent(certPath, parent));
+    Assertions.assertFalse(Certificates.containsParent(cert, certPath));
+    Assertions.assertTrue(Certificates.containsParent(certPath, certPath));
+    Assertions.assertTrue(Certificates.containsParent(cert, cert));
+  }
+
+  @Test
+  public void isSelfSigned() throws Exception {
+    var certPath =
+        Certificates.fromPemChain(Resources.toByteArray(Resources.getResource(CERT_CHAIN)));
+    var cert = Certificates.fromPem(Resources.toByteArray(Resources.getResource(CERT)));
+
+    Assertions.assertTrue(Certificates.isSelfSigned(certPath));
+    Assertions.assertFalse(Certificates.isSelfSigned(cert));
   }
 }