diff --git a/crypto/signature.go b/crypto/signature.go
index fa050f0..8718505 100644
--- a/crypto/signature.go
+++ b/crypto/signature.go
@@ -48,12 +48,7 @@ func (x *Signature) Calculate(signer Signer, data []byte) error {
 
 	m := (*refs.Signature)(x)
 
-	scheme := refs.SignatureScheme(signer.Scheme())
-	if scheme > 0 {
-		scheme-- // to sync numeric values
-	}
-
-	m.SetScheme(scheme)
+	m.SetScheme(refs.SignatureScheme(signer.Scheme()))
 	m.SetSign(signature)
 	m.SetKey(key)
 
@@ -69,7 +64,7 @@ func (x *Signature) Calculate(signer Signer, data []byte) error {
 func (x Signature) Verify(data []byte) bool {
 	m := (*refs.Signature)(&x)
 
-	f, ok := publicKeys[Scheme(m.GetScheme()+1)] // increment to sync numeric values
+	f, ok := publicKeys[Scheme(m.GetScheme())]
 	if !ok {
 		return false
 	}
diff --git a/crypto/signer.go b/crypto/signer.go
index ec55fbc..1972274 100644
--- a/crypto/signer.go
+++ b/crypto/signer.go
@@ -6,12 +6,12 @@ import (
 
 // Scheme represents digital signature algorithm with fixed cryptographic hash function.
 //
-// Non-positive values are reserved and depend on context (e.g. unsupported scheme).
-type Scheme uint32
+// Negative values are reserved and depend on context (e.g. unsupported scheme).
+type Scheme int32
 
 //nolint:revive
 const (
-	_ Scheme = iota
+	_ Scheme = iota - 1
 
 	ECDSA_SHA512               // ECDSA with SHA-512 hashing (FIPS 186-3)
 	ECDSA_DETERMINISTIC_SHA256 // Deterministic ECDSA with SHA-256 hashing (RFC 6979)