From 018e0d9edfd212c866063e04297a59b500b2c393 Mon Sep 17 00:00:00 2001
From: Daniel Gultsch <daniel@gultsch.de>
Date: Wed, 7 Sep 2022 11:08:54 +0200
Subject: [PATCH] add (inactive) channel binding end-point code

---
 .../crypto/sasl/ScramPlusMechanism.java       | 63 +++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramPlusMechanism.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramPlusMechanism.java
index 8f6dec20e..8de4524f2 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramPlusMechanism.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramPlusMechanism.java
@@ -1,11 +1,24 @@
 package eu.siacs.conversations.crypto.sasl;
 
+import android.util.Log;
+
+import org.bouncycastle.jcajce.provider.digest.SHA256;
 import org.conscrypt.Conscrypt;
 
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.cert.Certificate;
+import java.security.cert.CertificateEncodingException;
+import java.security.cert.X509Certificate;
+
 import javax.net.ssl.SSLException;
+import javax.net.ssl.SSLPeerUnverifiedException;
+import javax.net.ssl.SSLSession;
 import javax.net.ssl.SSLSocket;
 
+import eu.siacs.conversations.Config;
 import eu.siacs.conversations.entities.Account;
+import eu.siacs.conversations.utils.CryptoHelper;
 
 abstract class ScramPlusMechanism extends ScramMechanism {
 
@@ -41,9 +54,59 @@ abstract class ScramPlusMechanism extends ScramMechanism {
                         "Could not retrieve tls unique. Socket not ready");
             }
             return unique;
+        } else if (this.channelBinding == ChannelBinding.TLS_SERVER_END_POINT) {
+            final byte[] endPoint = getServerEndPointChannelBinding(sslSocket.getSession());
+            Log.d(Config.LOGTAG, "retrieved endpoint " + CryptoHelper.bytesToHex(endPoint));
+            return endPoint;
         } else {
             throw new AuthenticationException(
                     String.format("%s is not a valid channel binding", ChannelBinding.NONE));
         }
     }
+
+    private byte[] getServerEndPointChannelBinding(final SSLSession session)
+            throws AuthenticationException {
+        final Certificate[] certificates;
+        try {
+            certificates = session.getPeerCertificates();
+        } catch (final SSLPeerUnverifiedException e) {
+            throw new AuthenticationException("Could not verify peer certificates");
+        }
+        if (certificates == null || certificates.length == 0) {
+            throw new AuthenticationException("Could not retrieve peer certificate");
+        }
+        final X509Certificate certificate;
+        if (certificates[0] instanceof X509Certificate) {
+            certificate = (X509Certificate) certificates[0];
+        } else {
+            throw new AuthenticationException("Certificate was not X509");
+        }
+        final String algorithm = certificate.getSigAlgName();
+        final int withIndex = algorithm.indexOf("with");
+        if (withIndex <= 0) {
+            throw new AuthenticationException("Unable to parse SigAlgName");
+        }
+        final String hashAlgorithm = algorithm.substring(0, withIndex);
+        final MessageDigest messageDigest;
+        // https://www.rfc-editor.org/rfc/rfc5929#section-4.1
+        if ("MD5".equalsIgnoreCase(hashAlgorithm) || "SHA1".equalsIgnoreCase(hashAlgorithm)) {
+            messageDigest = new SHA256.Digest();
+        } else {
+            try {
+                messageDigest = MessageDigest.getInstance(hashAlgorithm);
+            } catch (final NoSuchAlgorithmException e) {
+                throw new AuthenticationException(
+                        "Could not instantiate message digest for " + hashAlgorithm);
+            }
+        }
+        Log.d(Config.LOGTAG, "hashing certificate with " + messageDigest.getAlgorithm());
+        final byte[] encodedCertificate;
+        try {
+            encodedCertificate = certificate.getEncoded();
+        } catch (final CertificateEncodingException e) {
+            throw new AuthenticationException("Could not encode certificate");
+        }
+        messageDigest.update(encodedCertificate);
+        return messageDigest.digest();
+    }
 }