GH-525: Fix sntrup761x25519-sha512

CHANGES.md

@@ -34,6 +34,8 @@
 
 ## Bug Fixes
 
+* [GH-525](https://github.com/apache/mina-sshd/issues/525) Fix sntrup761x25519-sha512 key exchange
+
 ## New Features
 
 ## Potential compatibility issues

sshd-core/src/main/java/org/apache/sshd/common/kex/BuiltinDHFactories.java

@@ -253,7 +253,7 @@ public XDH create(Object... params) throws Exception {
             if (!GenericUtils.isEmpty(params)) {
                 throw new IllegalArgumentException("No accepted parameters for " + getName());
             }
-            return new XDH(MontgomeryCurve.x25519) {
+            return new XDH(MontgomeryCurve.x25519, false) {
 
                 @Override
                 public Digest getHash() throws Exception {
@@ -274,7 +274,7 @@ public XDH create(Object... params) throws Exception {
             if (!GenericUtils.isEmpty(params)) {
                 throw new IllegalArgumentException("No accepted parameters for " + getName());
             }
-            return new XDH(MontgomeryCurve.x25519) {
+            return new XDH(MontgomeryCurve.x25519, false) {
 
                 @Override
                 public Digest getHash() throws Exception {
@@ -298,7 +298,7 @@ public XDH create(Object... params) throws Exception {
             if (!GenericUtils.isEmpty(params)) {
                 throw new IllegalArgumentException("No accepted parameters for " + getName());
             }
-            return new XDH(MontgomeryCurve.x448) {
+            return new XDH(MontgomeryCurve.x448, false) {
 
                 @Override
                 public Digest getHash() throws Exception {
@@ -322,7 +322,7 @@ public XDH create(Object... params) throws Exception {
             if (!GenericUtils.isEmpty(params)) {
                 throw new IllegalArgumentException("No accepted parameters for " + getName());
             }
-            return new XDH(MontgomeryCurve.x25519) {
+            return new XDH(MontgomeryCurve.x25519, true) {
 
                 @Override
                 public KeyEncapsulationMethod getKeyEncapsulation() {

sshd-core/src/main/java/org/apache/sshd/common/kex/XDH.java

@@ -31,11 +31,13 @@
  */
 public abstract class XDH extends AbstractDH {
 
-    protected MontgomeryCurve curve;
+    protected final MontgomeryCurve curve;
+    protected final boolean raw;
     protected byte[] f;
 
-    public XDH(MontgomeryCurve curve) throws Exception {
+    public XDH(MontgomeryCurve curve, boolean raw) throws Exception {
         this.curve = Objects.requireNonNull(curve, "No MontgomeryCurve provided");
+        this.raw = raw;
         myKeyAgree = curve.createKeyAgreement();
     }
 
@@ -77,6 +79,7 @@ public void putF(Buffer buffer, byte[] f) {
     protected byte[] calculateK() throws Exception {
         Objects.requireNonNull(f, "Missing 'f' value");
         myKeyAgree.doPhase(curve.decode(f), true);
-        return stripLeadingZeroes(myKeyAgree.generateSecret());
+        byte[] secret = myKeyAgree.generateSecret();
+        return raw ? secret : stripLeadingZeroes(secret);
     }
 }

sshd-core/src/main/java/org/apache/sshd/common/session/helpers/SessionHelper.java

@@ -758,7 +758,7 @@ protected byte[] resizeKey(
                 buffer = new ByteArrayBuffer();
             }
 
-            buffer.putMPInt(k);
+            buffer.putBytes(k);
             buffer.putRawBytes(h);
             buffer.putRawBytes(e);
             hash.update(buffer.array(), 0, buffer.available());