Export Schnorr signature API (#32)

Implement Schnorr signatures (BIP 340)

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

@@ -38,6 +38,24 @@ public interface Secp256k1 {
     public fun sign(message: ByteArray, privkey: ByteArray): ByteArray
 
     /**
+     * Verify a Schnorr signature.
+     *
+     * @param signature 64 bytes signature.
+     * @param message message signed.
+     * @param pubkey signer's x-only public key (32 bytes).
+     */
+    public fun verifySchnorr(signature: ByteArray, data: ByteArray, pub: ByteArray): Boolean
+
+    /**
+     * Create a Schnorr signature.
+     *
+     * @param message message to sign.
+     * @param privkey signer's private key.
+     * @param auxrand32 32 bytes of fresh randomness (optional).
+     */
+    public fun signSchnorr(data: ByteArray, sec: ByteArray, auxrand32: ByteArray?): ByteArray
+
+   /**
      * Convert an ECDSA signature to a normalized lower-S form (bitcoin standardness rule).
      * Returns the normalized signature and a boolean set to true if the input signature was not normalized.
      *

src/nativeInterop/cinterop/libsecp256k1.def

@@ -1,7 +1,7 @@
 package = secp256k1
 
-headers = secp256k1.h secp256k1_ecdh.h secp256k1_recovery.h
-headerFilter = secp256k1/** secp256k1_ecdh.h secp256k1_recovery.h secp256k1.h
+headers = secp256k1.h secp256k1_ecdh.h secp256k1_recovery.h secp256k1_extrakeys.h secp256k1_schnorrsig.h
+headerFilter = secp256k1/** secp256k1_ecdh.h secp256k1_recovery.h secp256k1_extrakeys.h secp256k1_schnorrsig.h secp256k1.h
 
 libraryPaths.linux = c/secp256k1/build/linux/
 linkerOpts.linux = -L/usr/lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/local/lib

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

@@ -222,9 +222,41 @@ public object Secp256k1Native : Secp256k1 {
         }
     }
 
+    override fun verifySchnorr(signature: ByteArray, data: ByteArray, pub: ByteArray): Boolean {
+        require(signature.size == 64)
+        require(data.size == 32)
+        require(pub.size == 32)
+        memScoped {
+            val nPub = toNat(pub)
+            val pubkey = alloc<secp256k1_xonly_pubkey>()
+            secp256k1_xonly_pubkey_parse(ctx, pubkey.ptr, nPub).requireSuccess("secp256k1_xonly_pubkey_parse() failed")
+            val nData = toNat(data)
+            val nSig = toNat(signature)
+            return secp256k1_schnorrsig_verify(ctx, nSig, nData, 32, pubkey.ptr) == 1
+        }
+    }
+
+    override fun signSchnorr(data: ByteArray, sec: ByteArray, auxrand32: ByteArray?): ByteArray {
+        require(sec.size == 32)
+        require(data.size == 32)
+        auxrand32?.let { require(it.size == 32) }
+        memScoped {
+            val nSec = toNat(sec)
+            val nData = toNat(data)
+            val nAuxrand32 = auxrand32?.let { toNat(it) }
+            val nSig = allocArray<UByteVar>(64)
+            val keypair = alloc<secp256k1_keypair>()
+            secp256k1_keypair_create(ctx, keypair.ptr, nSec).requireSuccess("secp256k1_keypair_create() failed")
+            secp256k1_schnorrsig_sign(ctx, nSig, nData, keypair.ptr, nAuxrand32).requireSuccess("secp256k1_ecdsa_sign() failed")
+            return nSig.readBytes(64)
+        }
+    }
+    
     public override fun cleanup() {
         secp256k1_context_destroy(ctx)
     }
+
+
 }
 
 internal actual fun getSecpk256k1(): Secp256k1 = Secp256k1Native