Add compact2der() method

jni/c/headers/java/fr_acinq_secp256k1_Secp256k1CFunctions.h

@@ -151,6 +151,14 @@ JNIEXPORT jbyteArray JNICALL Java_fr_acinq_secp256k1_Secp256k1CFunctions_secp256
 JNIEXPORT jbyteArray JNICALL Java_fr_acinq_secp256k1_Secp256k1CFunctions_secp256k1_1ecdsa_1recover
   (JNIEnv *, jclass, jlong, jbyteArray, jbyteArray, jint);
 
+/*
+ * Class:     fr_acinq_secp256k1_Secp256k1CFunctions
+ * Method:    secp256k1_compact_to_der
+ * Signature: (J[B)[B
+ */
+JNIEXPORT jbyteArray JNICALL Java_fr_acinq_secp256k1_Secp256k1CFunctions_secp256k1_1compact_1to_1der
+  (JNIEnv *, jclass, jlong, jbyteArray);
+
 #ifdef __cplusplus
 }
 #endif

jni/c/src/fr_acinq_secp256k1_Secp256k1CFunctions.c

@@ -687,3 +687,38 @@ JNIEXPORT jbyteArray JNICALL Java_fr_acinq_secp256k1_Secp256k1CFunctions_secp256
     CHECKRESULT(!result, "secp256k1_ec_pubkey_serialize failed");
     return jpubkey;
 }
+
+/*
+ * Class:     fr_acinq_secp256k1_Secp256k1CFunctions
+ * Method:    secp256k1_compact_to_der
+ * Signature: (J[B)[B
+ */
+JNIEXPORT jbyteArray JNICALL Java_fr_acinq_secp256k1_Secp256k1CFunctions_secp256k1_1compact_1to_1der
+  (JNIEnv *penv, jclass clazz, jlong jctx, jbyteArray jsig)
+{
+    secp256k1_context* ctx = (secp256k1_context *)jctx;
+    jbyte *sig;
+    secp256k1_ecdsa_signature signature;;
+    unsigned char der[73];
+    size_t size;
+    int result = 0;
+
+    if (jctx == 0) return 0;
+    if (jsig == NULL) return 0;
+    CHECKRESULT((*penv)->GetArrayLength(penv, jsig) != 64, "invalid signature size");
+
+    size = (*penv)->GetArrayLength(penv, jsig);
+    sig = (*penv)->GetByteArrayElements(penv, jsig, 0);
+    result = secp256k1_ecdsa_signature_parse_compact(ctx, &signature, (unsigned char*)sig);
+    (*penv)->ReleaseByteArrayElements(penv, jsig, sig, 0);
+    CHECKRESULT(!result, "secp256k1_ecdsa_signature_parse_compact failed");
+
+    size = 73;
+    result = secp256k1_ecdsa_signature_serialize_der(ctx, der, &size, &signature);
+    CHECKRESULT(!result, "secp256k1_ecdsa_signature_serialize_der failed");
+    jsig = (*penv)->NewByteArray(penv, size);
+    sig = (*penv)->GetByteArrayElements(penv, jsig, 0);
+    memcpy(sig, der, size);
+    (*penv)->ReleaseByteArrayElements(penv, jsig, sig, 0);
+    return jsig;
+}

jni/src/main/java/fr/acinq/secp256k1/Secp256k1CFunctions.java

@@ -64,4 +64,6 @@ public class Secp256k1CFunctions {
     public static native byte[] secp256k1_ecdh(long ctx, byte[] seckey, byte[] pubkey);
 
     public static native byte[] secp256k1_ecdsa_recover(long ctx, byte[] sig, byte[] msg32, int recid);
+
+    public static native byte[] secp256k1_compact_to_der(long ctx, byte[] sig);
 }

jni/src/main/kotlin/fr/acinq/secp256k1/NativeSecp256k1.kt

@@ -83,4 +83,8 @@ public object NativeSecp256k1 : Secp256k1 {
     override fun ecdsaRecover(sig: ByteArray, message: ByteArray, recid: Int): ByteArray {
         return Secp256k1CFunctions.secp256k1_ecdsa_recover(Secp256k1Context.getContext(), sig, message, recid)
     }
+
+    override fun compact2der(sig: ByteArray): ByteArray {
+        return Secp256k1CFunctions.secp256k1_compact_to_der(Secp256k1Context.getContext(), sig)
+    }
 }

src/commonMain/kotlin/fr/acinq/secp256k1/Secp256k1.kt

@@ -52,6 +52,8 @@ public interface Secp256k1 {
 
     public fun ecdsaRecover(sig: ByteArray, message: ByteArray, recid: Int): ByteArray
 
+    public fun compact2der(sig: ByteArray): ByteArray
+
     public fun pubKeyCompress(pubkey: ByteArray) : ByteArray {
         return when {
             pubkey.size == 33 && (pubkey[0] == 2.toByte() || pubkey[0] == 3.toByte()) -> pubkey

src/nativeMain/kotlin/fr/acinq/secp256k1/Secp256k1Native.kt

@@ -215,6 +215,18 @@ public object Secp256k1Native : Secp256k1 {
             return serializePubkey(pubkey)
         }
     }
+
+    public override fun compact2der(sig: ByteArray): ByteArray {
+        require(sig.size == 64)
+        memScoped {
+            val nSig = allocSignature(sig)
+            val natOutput = allocArray<UByteVar>(73)
+            val len = alloc<size_tVar>()
+            len.value = 73.convert()
+            secp256k1_ecdsa_signature_serialize_der(ctx, natOutput, len.ptr, nSig.ptr).requireSuccess("secp256k1_ecdsa_signature_serialize_der() failed")
+            return natOutput.readBytes(len.value.toInt())
+        }
+    }
 }
 
 internal actual fun getSecpk256k1(): Secp256k1 = Secp256k1Native

tests/src/commonTest/kotlin/fr/acinq/secp256k1/Secp256k1Test.kt

@@ -255,4 +255,14 @@ class Secp256k1Test {
         val pub1: ByteArray = Secp256k1.ecdsaRecover(sig, data, 1)
         assertTrue(pub.contentEquals(pub0) || pub.contentEquals(pub1), "testEcdsaRecover")
     }
+
+    @Test
+    fun testCompactToDER() {
+        val sig: ByteArray = Hex.decode("182A108E1448DC8F1FB467D06A0F3BB8EA0533584CB954EF8DA112F1D60E39A21C66F36DA211C087F3AF88B50EDF4F9BDAA6CF5FD6817E74DCA34DB12390C6E9".toLowerCase()) //sha256hash of "testing"
+        val der: ByteArray = Secp256k1.compact2der(sig)
+        assertEquals(
+            "30440220182A108E1448DC8F1FB467D06A0F3BB8EA0533584CB954EF8DA112F1D60E39A202201C66F36DA211C087F3AF88B50EDF4F9BDAA6CF5FD6817E74DCA34DB12390C6E9",
+            Hex.encode(der).toUpperCase(),
+        )
+    }
 }