feat(crypto): add wrapers for BIP-340 compatible Schnorr signatures from secp256k1_zkp

crypto/Makefile

@@ -44,7 +44,9 @@ ZKP_CFLAGS = \
 	-DECMULT_GEN_PREC_BITS=4 \
 	-DECMULT_WINDOW_SIZE=8 \
 	-DENABLE_MODULE_GENERATOR \
-	-DENABLE_MODULE_RECOVERY
+	-DENABLE_MODULE_RECOVERY \
+	-DENABLE_MODULE_SCHNORRSIG \
+	-DENABLE_MODULE_EXTRAKEYS
 ZKP_PATH = ../vendor/secp256k1-zkp
 CFLAGS += -DSECP256K1_CONTEXT_SIZE=73952
 
@@ -97,6 +99,7 @@ SRCS  += slip39.c
 SRCS  += schnorr.c
 SRCS  += zkp_context.c
 SRCS  += zkp_ecdsa.c
+SRCS  += zkp_schnorr.c
 
 OBJS   = $(SRCS:.c=.o)
 OBJS  += secp256k1-zkp.o

crypto/zkp_schnorr.c

@@ -0,0 +1,146 @@
+/**
+ * Copyright (c) SatoshiLabs
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdbool.h>
+#include <string.h>
+
+#include "memzero.h"
+#include "zkp_context.h"
+
+#include "vendor/secp256k1-zkp/include/secp256k1.h"
+#include "vendor/secp256k1-zkp/include/secp256k1_extrakeys.h"
+#include "vendor/secp256k1-zkp/include/secp256k1_schnorrsig.h"
+
+#include "zkp_schnorr.h"
+
+// BIP340 Schnorr public key derivation
+// private_key_bytes has 32 bytes
+// public_key_bytes has 32 bytes
+int zkp_schnorr_get_public_key(const uint8_t *private_key_bytes,
+                               uint8_t *public_key_bytes) {
+  int result = 0;
+
+  secp256k1_pubkey pubkey = {0};
+
+  if (result == 0) {
+    secp256k1_context *context_writable = zkp_context_acquire_writable();
+    secp256k1_context_writable_randomize(context_writable);
+    if (secp256k1_ec_pubkey_create(context_writable, &pubkey,
+                                   private_key_bytes) != 1) {
+      result = -1;
+    }
+    zkp_context_release_writable();
+  }
+
+  secp256k1_xonly_pubkey xonly_pubkey = {0};
+  const secp256k1_context *context_read_only = zkp_context_get_read_only();
+
+  if (result == 0) {
+    if (secp256k1_xonly_pubkey_from_pubkey(context_read_only, &xonly_pubkey,
+                                           NULL, &pubkey) != 1) {
+      result = -1;
+    }
+  }
+
+  memzero(&pubkey, sizeof(pubkey));
+
+  if (result == 0) {
+    if (secp256k1_xonly_pubkey_serialize(context_read_only, public_key_bytes,
+                                         &xonly_pubkey) != 1) {
+      result = -1;
+    }
+  }
+
+  memzero(&xonly_pubkey, sizeof(xonly_pubkey));
+
+  return result;
+}
+
+// BIP340 Schnorr signature signing
+// private_key_bytes has 32 bytes
+// digest has 32 bytes
+// signature_bytes has 64 bytes
+// auxiliary_data has 32 bytes or is NULL
+// returns 0 on success
+int zkp_schnorr_sign_digest(const uint8_t *private_key_bytes,
+                            const uint8_t *digest, uint8_t *signature_bytes,
+                            uint8_t *auxiliary_data) {
+  int result = 0;
+
+  secp256k1_keypair keypair = {0};
+
+  if (result == 0) {
+    secp256k1_context *context_writable = zkp_context_acquire_writable();
+    secp256k1_context_writable_randomize(context_writable);
+    if (secp256k1_keypair_create(context_writable, &keypair,
+                                 private_key_bytes) != 1) {
+      result = -1;
+    }
+    zkp_context_release_writable();
+  }
+
+  if (result == 0) {
+    secp256k1_context *context_writable = zkp_context_acquire_writable();
+    secp256k1_context_writable_randomize(context_writable);
+    if (secp256k1_schnorrsig_sign(context_writable, signature_bytes, digest,
+                                  &keypair, NULL, auxiliary_data) != 1) {
+      result = -1;
+    }
+    zkp_context_release_writable();
+  }
+
+  memzero(&keypair, sizeof(keypair));
+
+  return result;
+}
+
+// BIP340 Schnorr signature verification
+// public_key_bytes has 32 bytes
+// signature_bytes has 64 bytes
+// digest has 32 bytes
+// returns 0 if verification succeeded
+int zkp_schnorr_verify_digest(const uint8_t *public_key_bytes,
+                              const uint8_t *signature_bytes,
+                              const uint8_t *digest) {
+  int result = 0;
+
+  secp256k1_xonly_pubkey xonly_pubkey = {0};
+  const secp256k1_context *context_read_only = zkp_context_get_read_only();
+
+  if (result == 0) {
+    if (secp256k1_xonly_pubkey_parse(context_read_only, &xonly_pubkey,
+                                     public_key_bytes) != 1) {
+      result = 1;
+    }
+  }
+
+  if (result == 0) {
+    if (secp256k1_schnorrsig_verify(context_read_only, signature_bytes, digest,
+                                    &xonly_pubkey) != 1) {
+      result = 5;
+    }
+  }
+
+  memzero(&xonly_pubkey, sizeof(xonly_pubkey));
+
+  return result;
+}

crypto/zkp_schnorr.h

@@ -0,0 +1,15 @@
+#ifndef __ZKP_SCHNORR_H__
+#define __ZKP_SCHNORR_H__
+
+#include <stdint.h>
+
+int zkp_schnorr_get_public_key(const uint8_t *private_key_bytes,
+                               uint8_t *public_key_bytes);
+int zkp_schnorr_sign_digest(const uint8_t *private_key_bytes,
+                            const uint8_t *digest, uint8_t *signature_bytes,
+                            uint8_t *auxiliary_data);
+int zkp_schnorr_verify_digest(const uint8_t *public_key_bytes,
+                              const uint8_t *signature_bytes,
+                              const uint8_t *digest);
+
+#endif