signature_libsecp256k1.go raw

   1  //go:build libsecp256k1
   2  
   3  package nostr
   4  
   5  /*
   6  #cgo CFLAGS: -I${SRCDIR}/libsecp256k1/include -I${SRCDIR}/libsecp256k1/src
   7  #cgo CFLAGS: -DECMULT_GEN_PREC_BITS=4
   8  #cgo CFLAGS: -DECMULT_WINDOW_SIZE=15
   9  #cgo CFLAGS: -DENABLE_MODULE_SCHNORRSIG=1
  10  #cgo CFLAGS: -DENABLE_MODULE_EXTRAKEYS=1
  11  
  12  #include "./libsecp256k1/src/secp256k1.c"
  13  #include "./libsecp256k1/src/precomputed_ecmult.c"
  14  #include "./libsecp256k1/src/precomputed_ecmult_gen.c"
  15  #include "./libsecp256k1/src/ecmult_gen.h"
  16  #include "./libsecp256k1/src/ecmult.h"
  17  #include "./libsecp256k1/src/modules/extrakeys/main_impl.h"
  18  #include "./libsecp256k1/src/modules/schnorrsig/main_impl.h"
  19  
  20  #include "./libsecp256k1/include/secp256k1.h"
  21  #include "./libsecp256k1/include/secp256k1_extrakeys.h"
  22  #include "./libsecp256k1/include/secp256k1_schnorrsig.h"
  23  */
  24  import "C"
  25  
  26  import (
  27  	"crypto/rand"
  28  	"crypto/sha256"
  29  	"encoding/hex"
  30  	"errors"
  31  	"fmt"
  32  	"unsafe"
  33  
  34  	"github.com/btcsuite/btcd/btcec/v2/schnorr"
  35  )
  36  
  37  func (evt Event) CheckSignature() (bool, error) {
  38  	var pk [32]byte
  39  	_, err := hex.Decode(pk[:], []byte(evt.PubKey))
  40  	if err != nil {
  41  		return false, fmt.Errorf("event pubkey '%s' is invalid hex: %w", evt.PubKey, err)
  42  	}
  43  
  44  	var sig [64]byte
  45  	_, err = hex.Decode(sig[:], []byte(evt.Sig))
  46  	if err != nil {
  47  		return false, fmt.Errorf("event signature '%s' is invalid hex: %w", evt.Sig, err)
  48  	}
  49  
  50  	msg := sha256.Sum256(evt.Serialize())
  51  
  52  	var xonly C.secp256k1_xonly_pubkey
  53  	if C.secp256k1_xonly_pubkey_parse(globalSecp256k1Context, &xonly, (*C.uchar)(unsafe.Pointer(&pk[0]))) != 1 {
  54  		return false, fmt.Errorf("failed to parse xonly pubkey")
  55  	}
  56  
  57  	res := C.secp256k1_schnorrsig_verify(globalSecp256k1Context, (*C.uchar)(unsafe.Pointer(&sig[0])), (*C.uchar)(unsafe.Pointer(&msg[0])), 32, &xonly)
  58  	return res == 1, nil
  59  }
  60  
  61  func (evt *Event) Sign(secretKey string, signOpts ...schnorr.SignOption) error {
  62  	sk, err := hex.DecodeString(secretKey)
  63  	if err != nil {
  64  		return fmt.Errorf("Sign called with invalid secret key '%s': %w", secretKey, err)
  65  	}
  66  
  67  	if evt.Tags == nil {
  68  		evt.Tags = make(Tags, 0)
  69  	}
  70  
  71  	var keypair C.secp256k1_keypair
  72  	if C.secp256k1_keypair_create(globalSecp256k1Context, &keypair, (*C.uchar)(unsafe.Pointer(&sk[0]))) != 1 {
  73  		return errors.New("failed to parse private key")
  74  	}
  75  
  76  	var xonly C.secp256k1_xonly_pubkey
  77  	var pk [32]byte
  78  	C.secp256k1_keypair_xonly_pub(globalSecp256k1Context, &xonly, nil, &keypair)
  79  	C.secp256k1_xonly_pubkey_serialize(globalSecp256k1Context, (*C.uchar)(unsafe.Pointer(&pk[0])), &xonly)
  80  	evt.PubKey = hex.EncodeToString(pk[:])
  81  
  82  	h := sha256.Sum256(evt.Serialize())
  83  
  84  	var sig [64]byte
  85  	var random [32]byte
  86  	rand.Read(random[:])
  87  	if C.secp256k1_schnorrsig_sign32(globalSecp256k1Context, (*C.uchar)(unsafe.Pointer(&sig[0])), (*C.uchar)(unsafe.Pointer(&h[0])), &keypair, (*C.uchar)(unsafe.Pointer(&random[0]))) != 1 {
  88  		return errors.New("failed to sign message")
  89  	}
  90  
  91  	evt.ID = hex.EncodeToString(h[:])
  92  	evt.Sig = hex.EncodeToString(sig[:])
  93  
  94  	return nil
  95  }
  96  
  97  var globalSecp256k1Context *C.secp256k1_context
  98  
  99  func init() {
 100  	globalSecp256k1Context = C.secp256k1_context_create(C.SECP256K1_CONTEXT_SIGN | C.SECP256K1_CONTEXT_VERIFY)
 101  	if globalSecp256k1Context == nil {
 102  		panic("failed to create secp256k1 context")
 103  	}
 104  }
 105