[#190] crypto: Replace public key encoding methods to `PublicKey`

This make `neofscrypto.Signer` interface more similar to the one from
standard `crypto` package.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

crypto/ecdsa/public.go

@@ -5,6 +5,7 @@ import (
 	"crypto/elliptic"
 	"crypto/sha256"
 	"crypto/sha512"
+	"fmt"
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
@@ -21,6 +22,11 @@ type PublicKey struct {
 	key ecdsa.PublicKey
 }
 
+// SetKey specifies ecdsa.PublicKey to be used for ECDSA signature verification.
+func (x *PublicKey) SetKey(key ecdsa.PublicKey) {
+	x.key = key
+}
+
 // MakeDeterministic makes PublicKey to use Deterministic ECDSA scheme
 // (see neofscrypto.ECDSA_DETERMINISTIC_SHA256). By default,
 // neofscrypto.ECDSA_SHA512 is used.
@@ -28,9 +34,28 @@ func (x *PublicKey) MakeDeterministic() {
 	x.deterministic = true
 }
 
+// MaxEncodedSize returns size of the compressed ECDSA public key.
+func (x PublicKey) MaxEncodedSize() int {
+	return 33
+}
+
+// Encode encodes ECDSA public key in compressed form into buf.
+// Uses exactly MaxEncodedSize bytes of the buf.
+//
+// Encode panics if buf length is less than MaxEncodedSize.
+//
+// See also Decode.
+func (x PublicKey) Encode(buf []byte) int {
+	if len(buf) < 33 {
+		panic(fmt.Sprintf("too short buffer %d", len(buf)))
+	}
+
+	return copy(buf, (*keys.PublicKey)(&x.key).Bytes())
+}
+
 // Decode decodes compressed binary representation of the PublicKey.
 //
-// See also Signer.EncodePublicKey.
+// See also Encode.
 func (x *PublicKey) Decode(data []byte) error {
 	pub, err := keys.NewPublicKeyFromBytes(data, elliptic.P256())
 	if err != nil {

crypto/ecdsa/signer.go

@@ -5,7 +5,6 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/sha512"
-	"fmt"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	neofscrypto "github.com/nspcc-dev/neofs-sdk-go/crypto"
@@ -65,22 +64,13 @@ func (x Signer) Sign(data []byte) ([]byte, error) {
 	return elliptic.Marshal(elliptic.P256(), r, s), nil
 }
 
-// MaxPublicKeyEncodedSize returns size of the compressed ECDSA public key
-// of the Signer.
-func (x Signer) MaxPublicKeyEncodedSize() int {
-	return 33
-}
+func (x Signer) Public() neofscrypto.PublicKey {
+	var pub PublicKey
+	pub.SetKey(x.key.PublicKey)
 
-// EncodePublicKey encodes ECDSA public key of the Signer in compressed form
-// into buf. Uses exactly MaxPublicKeyEncodedSize bytes of the buf.
-//
-// EncodePublicKey panics if buf length is less than MaxPublicKeyEncodedSize.
-//
-// See also PublicKey.Decode.
-func (x Signer) EncodePublicKey(buf []byte) int {
-	if len(buf) < 33 {
-		panic(fmt.Sprintf("too short buffer %d", len(buf)))
+	if x.deterministic {
+		pub.MakeDeterministic()
 	}
 
-	return copy(buf, (*keys.PublicKey)(&x.key.PublicKey).Bytes())
+	return &pub
 }

crypto/signature.go

@@ -43,8 +43,10 @@ func (x *Signature) Calculate(signer Signer, data []byte) error {
 		return fmt.Errorf("signer %T failure: %w", signer, err)
 	}
 
-	key := make([]byte, signer.MaxPublicKeyEncodedSize())
-	key = key[:signer.EncodePublicKey(key)]
+	pub := signer.Public()
+
+	key := make([]byte, pub.MaxEncodedSize())
+	key = key[:pub.Encode(key)]
 
 	m := (*refs.Signature)(x)
 

crypto/signer.go

@@ -55,23 +55,8 @@ type Signer interface {
 	// Sign signs SHA-256 hash of the data.
 	Sign(data []byte) ([]byte, error)
 
-	// MaxPublicKeyEncodedSize returns maximum size required for binary-encoded
-	// public key.
-	//
-	// MaxPublicKeyEncodedSize MUST NOT return value greater than any return of
-	// EncodePublicKey.
-	MaxPublicKeyEncodedSize() int
-
-	// EncodePublicKey encodes public key into buf. Returns number of bytes
-	// written.
-	//
-	// EncodePublicKey MUST panic if buffer size is insufficient and less than
-	// MaxPublicKeyEncodedSize (*). EncodePublicKey MUST return negative value
-	// on any failure except (*).
-	//
-	// EncodePublicKey is expected to be compatible with PublicKey.Decode for
-	// similar signature schemes.
-	EncodePublicKey(buf []byte) int
+	// Public returns the public key corresponding to the Signer.
+	Public() PublicKey
 }
 
 // PublicKey represents a public key using fixed signature scheme supported by
@@ -79,10 +64,26 @@ type Signer interface {
 //
 // See also Signer.
 type PublicKey interface {
+	// MaxEncodedSize returns maximum size required for binary-encoded
+	// public key.
+	//
+	// MaxEncodedSize MUST NOT return value greater than any return of
+	// Encode.
+	MaxEncodedSize() int
+
+	// Encode encodes public key into buf. Returns number of bytes
+	// written.
+	//
+	// Encode MUST panic if buffer size is insufficient and less than
+	// MaxEncodedSize (*). Encode MUST return negative value
+	// on any failure except (*).
+	//
+	// Encode is a reverse operation to Decode.
+	Encode(buf []byte) int
+
 	// Decode decodes binary public key.
 	//
-	// Decode is expected to be compatible with Signer.EncodePublicKey for
-	// similar signature schemes.
+	// Decode is a reverse operation to Encode.
 	Decode([]byte) error
 
 	// Verify checks signature of the given data. True means correct signature.