From 6a4770c23a48620a9951eeb5a31102caa32fedef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Richard=20K=C3=B6rber?= <github@shredzone.org>
Date: Sun, 18 Feb 2024 16:16:29 +0100
Subject: [PATCH] Get unique identifier according to draft-ietf-acme-ari-03

---
 .../shredzone/acme4j/toolbox/AcmeUtils.java   | 61 +++++++++++++++++++
 .../src/test/resources/ari-example-cert.pem   |  9 +++
 2 files changed, 70 insertions(+)
 create mode 100644 acme4j-client/src/test/resources/ari-example-cert.pem

diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/AcmeUtils.java b/acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/AcmeUtils.java
index 9752bd66..fd10cbc9 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/AcmeUtils.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/AcmeUtils.java
@@ -16,21 +16,29 @@ package org.shredzone.acme4j.toolbox;
 import static java.nio.charset.StandardCharsets.UTF_8;
 
 import java.io.IOException;
+import java.io.UncheckedIOException;
 import java.io.Writer;
 import java.net.IDN;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.security.cert.X509Certificate;
 import java.time.Instant;
 import java.time.ZoneId;
 import java.time.ZonedDateTime;
+import java.util.Arrays;
 import java.util.Base64;
 import java.util.Locale;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.regex.Pattern;
 
 import edu.umd.cs.findbugs.annotations.Nullable;
+import org.bouncycastle.asn1.ASN1Integer;
+import org.bouncycastle.asn1.x509.AuthorityKeyIdentifier;
+import org.bouncycastle.asn1.x509.Certificate;
+import org.bouncycastle.cert.X509CertificateHolder;
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 
 /**
@@ -323,4 +331,57 @@ public final class AcmeUtils {
         }
     }
 
+    /**
+     * Returns the certificate's unique identifier for renewal according to
+     * draft-ietf-acme-ari-03.
+     *
+     * @param certificate
+     *         Certificate to get the unique identifier for.
+     * @return Unique identifier
+     * @throws AcmeProtocolException
+     *         if the certificate is invalid or does not provide the necessary
+     *         information.
+     */
+    public static String getRenewalUniqueIdentifier(X509Certificate certificate) {
+        try {
+            var cert = new X509CertificateHolder(certificate.getEncoded());
+
+            var aki = Optional.of(cert)
+                    .map(X509CertificateHolder::getExtensions)
+                    .map(AuthorityKeyIdentifier::fromExtensions)
+                    .map(AuthorityKeyIdentifier::getKeyIdentifier)
+                    .map(AcmeUtils::base64UrlEncode)
+                    .orElseThrow(() -> new AcmeProtocolException("Missing or invalid Authority Key Identifier"));
+
+            var sn = Optional.of(cert)
+                    .map(X509CertificateHolder::toASN1Structure)
+                    .map(Certificate::getSerialNumber)
+                    .map(AcmeUtils::getRawInteger)
+                    .map(AcmeUtils::base64UrlEncode)
+                    .orElseThrow(() -> new AcmeProtocolException("Missing or invalid serial number"));
+
+            return aki + '.' + sn;
+        } catch (Exception ex) {
+            throw new AcmeProtocolException("Invalid certificate", ex);
+        }
+    }
+
+    /**
+     * Gets the raw integer array from ASN1Integer. This is done by encoding it to a byte
+     * array, and then skipping the INTEGER identifier. Other methods of ASN1Integer only
+     * deliver a parsed integer value that might have been mangled.
+     *
+     * @param integer
+     *         ASN1Integer to convert to raw
+     * @return Byte array of the raw integer
+     */
+    private static byte[] getRawInteger(ASN1Integer integer) {
+        try {
+            var encoded = integer.getEncoded();
+            return Arrays.copyOfRange(encoded, 2, encoded.length);
+        } catch (IOException ex) {
+            throw new UncheckedIOException(ex);
+        }
+    }
+
 }
diff --git a/acme4j-client/src/test/resources/ari-example-cert.pem b/acme4j-client/src/test/resources/ari-example-cert.pem
new file mode 100644
index 00000000..fe19f8a6
--- /dev/null
+++ b/acme4j-client/src/test/resources/ari-example-cert.pem
@@ -0,0 +1,9 @@
+-----BEGIN CERTIFICATE-----
+MIIBQzCB66ADAgECAgUAh2VDITAKBggqhkjOPQQDAjAVMRMwEQYDVQQDEwpFeGFt
+cGxlIENBMCIYDzAwMDEwMTAxMDAwMDAwWhgPMDAwMTAxMDEwMDAwMDBaMBYxFDAS
+BgNVBAMTC2V4YW1wbGUuY29tMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEeBZu
+7cbpAYNXZLbbh8rNIzuOoqOOtmxA1v7cRm//AwyMwWxyHz4zfwmBhcSrf47NUAFf
+qzLQ2PPQxdTXREYEnKMjMCEwHwYDVR0jBBgwFoAUaYhba4dGQEHhs3uEe6CuLN4B
+yNQwCgYIKoZIzj0EAwIDRwAwRAIge09+S5TZAlw5tgtiVvuERV6cT4mfutXIlwTb
++FYN/8oCIClDsqBklhB9KAelFiYt9+6FDj3z4KGVelYM5MdsO3pK
+-----END CERTIFICATE-----