[#157] signature: Change scheme selection

`SignData`: use `ECDSAWithSHA512` by default. `SignWithRFC6979` option
switches the scheme to `RFC6979WithSHA256`.

`VerifyData`: if scheme is not fixed (like by `SignWithRFC6979` option)
then scheme from the message is processed.

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

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/mr-tron/base58 v1.2.0
 	github.com/nspcc-dev/hrw v1.0.9
 	github.com/nspcc-dev/neo-go v0.98.0
-	github.com/nspcc-dev/neofs-api-go/v2 v2.12.0
+	github.com/nspcc-dev/neofs-api-go/v2 v2.11.2-0.20220302134950-d065453bd0a7
 	github.com/stretchr/testify v1.7.0
 	go.uber.org/zap v1.18.1
 	google.golang.org/grpc v1.41.0

signature/signature.go

@@ -12,11 +12,14 @@ type Scheme uint32
 
 // Supported signature schemes.
 const (
-	Unspecified Scheme = iota
-	ECDSAWithSHA512
+	ECDSAWithSHA512 Scheme = iota
 	RFC6979WithSHA256
 )
 
+func (x Scheme) String() string {
+	return refs.SignatureScheme(x).String()
+}
+
 // NewFromV2 wraps v2 Signature message to Signature.
 //
 // Nil refs.Signature converts to nil.

util/signature/data.go

@@ -57,7 +57,7 @@ func SignData(key *ecdsa.PrivateKey, src DataSource, opts ...SignOption) (*signa
 
 	cfg := getConfig(opts...)
 
-	sigData, err := sign(cfg.defaultScheme, key, data)
+	sigData, err := sign(cfg.scheme, key, data)
 	if err != nil {
 		return nil, err
 	}
@@ -65,7 +65,7 @@ func SignData(key *ecdsa.PrivateKey, src DataSource, opts ...SignOption) (*signa
 	sig := signature.New()
 	sig.SetKey((*keys.PublicKey)(&key.PublicKey).Bytes())
 	sig.SetSign(sigData)
-	sig.SetScheme(cfg.defaultScheme)
+	sig.SetScheme(cfg.scheme)
 	return sig, nil
 }
 

util/signature/options.go

@@ -16,14 +16,13 @@ import (
 var curve = elliptic.P256()
 
 type cfg struct {
-	defaultScheme  signature.Scheme
-	restrictScheme signature.Scheme
+	schemeFixed bool
+	scheme      signature.Scheme
 }
 
 func getConfig(opts ...SignOption) *cfg {
 	cfg := &cfg{
-		defaultScheme:  signature.ECDSAWithSHA512,
-		restrictScheme: signature.Unspecified,
+		scheme: signature.ECDSAWithSHA512,
 	}
 
 	for i := range opts {
@@ -46,7 +45,7 @@ func sign(scheme signature.Scheme, key *ecdsa.PrivateKey, msg []byte) ([]byte, e
 		p := &keys.PrivateKey{PrivateKey: *key}
 		return p.Sign(msg), nil
 	default:
-		panic("unsupported scheme")
+		panic(fmt.Sprintf("unsupported scheme %s", scheme))
 	}
 }
 
@@ -56,15 +55,11 @@ func verify(cfg *cfg, msg []byte, sig *signature.Signature) error {
 		return fmt.Errorf("%w: %v", ErrInvalidPublicKey, err)
 	}
 
-	scheme := sig.Scheme()
-	if scheme == signature.Unspecified {
-		scheme = cfg.defaultScheme
-	}
-	if cfg.restrictScheme != signature.Unspecified && scheme != cfg.restrictScheme {
-		return fmt.Errorf("%w: unexpected signature scheme", ErrInvalidSignature)
+	if !cfg.schemeFixed {
+		cfg.scheme = sig.Scheme()
 	}
 
-	switch scheme {
+	switch cfg.scheme {
 	case signature.ECDSAWithSHA512:
 		h := sha512.Sum512(msg)
 		r, s := unmarshalXY(sig.Sign())
@@ -79,7 +74,7 @@ func verify(cfg *cfg, msg []byte, sig *signature.Signature) error {
 		}
 		return ErrInvalidSignature
 	default:
-		return ErrInvalidSignature
+		return fmt.Errorf("unsupported signature scheme %s", cfg.scheme)
 	}
 }
 
@@ -111,7 +106,7 @@ func unmarshalXY(data []byte) (x *big.Int, y *big.Int) {
 
 func SignWithRFC6979() SignOption {
 	return func(c *cfg) {
-		c.defaultScheme = signature.RFC6979WithSHA256
-		c.restrictScheme = signature.RFC6979WithSHA256
+		c.schemeFixed = true
+		c.scheme = signature.RFC6979WithSHA256
 	}
 }