Ed25519 to Curve25519 keys conversion

src/main/java/org/abstractj/kalium/NaCl.java

@@ -499,6 +499,11 @@ int crypto_stream_xor(
         // ---------------------------------------------------------------------
         // Advanced: Ed25519 to Curve25519
 
+        int crypto_sign_ed25519_pk_to_curve25519(
+                @Out byte[] curve25519_pk, @In byte[] ed25519_pk);
+
+        int crypto_sign_ed25519_sk_to_curve25519(
+                @Out byte[] curve25519_sk, @In byte[] ed25519_sk);
     }
 
     /**

src/main/java/org/abstractj/kalium/keys/SigningKey.java

@@ -23,6 +23,7 @@
 
 import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_BOX_CURVE25519XSALSA20POLY1305_PUBLICKEYBYTES;
 import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_BOX_CURVE25519XSALSA20POLY1305_SECRETKEYBYTES;
+import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_SCALARMULT_CURVE25519_BYTES;
 import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_SIGN_ED25519_BYTES;
 import static org.abstractj.kalium.NaCl.sodium;
 import static org.abstractj.kalium.crypto.Util.checkLength;
@@ -60,6 +61,12 @@ public VerifyKey getVerifyKey() {
         return this.verifyKey;
     }
 
+    public PrivateKey convertToCurve() {
+        byte[] secretKey = zeros(CRYPTO_SCALARMULT_CURVE25519_BYTES);
+        sodium().crypto_sign_ed25519_sk_to_curve25519(secretKey, seed);
+        return new PrivateKey(secretKey);
+    }
+
     public byte[] sign(byte[] message) {
         byte[] signature = new byte[CRYPTO_SIGN_ED25519_BYTES];
         LongLongByReference bufferLen = new LongLongByReference(0);

src/main/java/org/abstractj/kalium/keys/VerifyKey.java

@@ -18,11 +18,9 @@
 
 import org.abstractj.kalium.encoders.Encoder;
 
-import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_BOX_CURVE25519XSALSA20POLY1305_PUBLICKEYBYTES;
-import static org.abstractj.kalium.NaCl.Sodium.CRYPTO_SIGN_ED25519_BYTES;
+import static org.abstractj.kalium.NaCl.Sodium.*;
 import static org.abstractj.kalium.NaCl.sodium;
-import static org.abstractj.kalium.crypto.Util.checkLength;
-import static org.abstractj.kalium.crypto.Util.isValid;
+import static org.abstractj.kalium.crypto.Util.*;
 import static org.abstractj.kalium.encoders.Encoder.HEX;
 
 public class VerifyKey {
@@ -38,6 +36,12 @@ public VerifyKey(String key, Encoder encoder) {
         this(encoder.decode(key));
     }
 
+    public PublicKey convertToCurve() {
+        byte[] publicKey = zeros(CRYPTO_SCALARMULT_CURVE25519_BYTES);
+        sodium().crypto_sign_ed25519_pk_to_curve25519(publicKey, key);
+        return new PublicKey(publicKey);
+    }
+
     public boolean verify(byte[] message, byte[] signature) {
         checkLength(signature, CRYPTO_SIGN_ED25519_BYTES);
         return isValid(sodium().crypto_sign_ed25519_verify_detached(signature, message, message.length, key), "signature was forged or corrupted");

src/test/java/org/abstractj/kalium/fixture/TestVectors.java

@@ -105,6 +105,7 @@ public class TestVectors {
     public static final String SECRET_KEY = "1b27556473e985d462cd51197a9a46c76009549eac6474f206c4ee0844f68389";
 
     public static final String SIGN_PRIVATE = "b18e1d0045995ec3d010c387ccfeb984d783af8fbb0f40fa7db126d889f6dadd";
+    public static final String SIGN_PRIVATE_CURVE25519 = "38e5cdf33bc9e13086f58a3fea86d574e85e7865cffa5e8c9335f200a41d036c";
     public static final String SIGN_MESSAGE = "916c7d1d268fc0e77c1bef238432573c39be577bbea0998936add2b50a653171" +
             "ce18a542b0b7f96c1691a3be6031522894a8634183eda38798a0c5d5d79fbd01" +
             "dd04a8646d71873b77b221998a81922d8105f892316369d5224c9983372d2313" +
@@ -113,7 +114,7 @@ public class TestVectors {
     public static final String SIGN_SIGNATURE = "6bd710a368c1249923fc7a1610747403040f0cc30815a00f9ff548a896bbda0b" +
             "4eb2ca19ebcf917f0f34200a9edbad3901b64ab09cc5ef7b9bcc3c40c0ff7509";
     public static final String SIGN_PUBLIC = "77f48b59caeda77751ed138b0ec667ff50f8768c25d48309a8f386a2bad187fb";
-
+    public static final String SIGN_PUBLIC_CURVE25519 = "35488a98f7ec26ae27099809afb27587b198b1197b5bcb0dec41153db2bf9952";
 
 
     /**

src/test/java/org/abstractj/kalium/keys/SigningKeyTest.java

@@ -137,6 +137,12 @@ public void testAccessVerifyKey() {
         assertEquals(v.toString(), SIGN_PUBLIC);
     }
 
+    @Test
+    public void testConvertToCurve() {
+        SigningKey key = new SigningKey(SIGN_PRIVATE, HEX);
+        assertEquals(key.convertToCurve().toString(), SIGN_PRIVATE_CURVE25519);
+    }
+
     @Test
     public void testRoundTrip() {
         SigningKey key = new SigningKey(SIGN_PRIVATE, HEX);

src/test/java/org/abstractj/kalium/keys/VerifyKeyTest.java

@@ -20,14 +20,9 @@
 
 import java.util.Arrays;
 
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.assertEquals;
 import static org.abstractj.kalium.encoders.Encoder.HEX;
-import static org.abstractj.kalium.fixture.TestVectors.SIGN_MESSAGE;
-import static org.abstractj.kalium.fixture.TestVectors.SIGN_PRIVATE;
-import static org.abstractj.kalium.fixture.TestVectors.SIGN_PUBLIC;
-import static org.abstractj.kalium.fixture.TestVectors.SIGN_SIGNATURE;
-import static org.junit.Assert.fail;
+import static org.abstractj.kalium.fixture.TestVectors.*;
+import static org.junit.Assert.*;
 
 public class VerifyKeyTest {
 
@@ -82,4 +77,10 @@ public void testInitializeFromHex() throws Exception {
         assertTrue(verifyKey.verify(SIGN_MESSAGE, SIGN_SIGNATURE, HEX));
     }
 
+    @Test
+    public void testConvertToCurve() {
+        VerifyKey verifyKey = new VerifyKey(SIGN_PUBLIC, HEX);
+        assertEquals(verifyKey.convertToCurve().toString(), SIGN_PUBLIC_CURVE25519);
+    }
+
 }