diff --git a/algo_eddsa.go b/algo_eddsa.go
index 5a37b20..207eca7 100644
--- a/algo_eddsa.go
+++ b/algo_eddsa.go
@@ -6,7 +6,7 @@ import (
 
 // NewSignerEdDSA returns a new ed25519-based signer.
 func NewSignerEdDSA(key ed25519.PrivateKey) (Signer, error) {
-	if key == nil {
+	if len(key) == 0 {
 		return nil, ErrInvalidKey
 	}
 	return &edDSAAlg{
@@ -17,7 +17,7 @@ func NewSignerEdDSA(key ed25519.PrivateKey) (Signer, error) {
 
 // NewVerifierEdDSA returns a new ed25519-based verifier.
 func NewVerifierEdDSA(key ed25519.PublicKey) (Verifier, error) {
-	if key == nil {
+	if len(key) == 0 {
 		return nil, ErrInvalidKey
 	}
 	return &edDSAAlg{
diff --git a/algo_es.go b/algo_es.go
index c22b73c..e4f9616 100644
--- a/algo_es.go
+++ b/algo_es.go
@@ -12,9 +12,9 @@ func NewSignerES(alg Algorithm, key *ecdsa.PrivateKey) (Signer, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getParamsES(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getParamsES(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &esAlg{
 		alg:        alg,
@@ -29,9 +29,9 @@ func NewVerifierES(alg Algorithm, key *ecdsa.PublicKey) (Verifier, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getParamsES(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getParamsES(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &esAlg{
 		alg:       alg,
@@ -41,16 +41,16 @@ func NewVerifierES(alg Algorithm, key *ecdsa.PublicKey) (Verifier, error) {
 	}, nil
 }
 
-func getParamsES(alg Algorithm) (crypto.Hash, error) {
+func getParamsES(alg Algorithm) (crypto.Hash, bool) {
 	switch alg {
 	case ES256:
-		return crypto.SHA256, nil
+		return crypto.SHA256, true
 	case ES384:
-		return crypto.SHA384, nil
+		return crypto.SHA384, true
 	case ES512:
-		return crypto.SHA512, nil
+		return crypto.SHA512, true
 	default:
-		return 0, ErrUnsupportedAlg
+		return 0, false
 	}
 }
 
diff --git a/algo_hs.go b/algo_hs.go
index 79cd564..3ab9c75 100644
--- a/algo_hs.go
+++ b/algo_hs.go
@@ -12,9 +12,9 @@ func NewSignerHS(alg Algorithm, key []byte) (Signer, error) {
 	if len(key) == 0 {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getHashHMAC(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getHashHMAC(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &hsAlg{
 		alg:  alg,
@@ -31,9 +31,9 @@ func NewVerifierHS(alg Algorithm, key []byte) (Verifier, error) {
 	if len(key) == 0 {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getHashHMAC(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getHashHMAC(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &hsAlg{
 		alg:  alg,
@@ -45,16 +45,16 @@ func NewVerifierHS(alg Algorithm, key []byte) (Verifier, error) {
 	}, nil
 }
 
-func getHashHMAC(alg Algorithm) (crypto.Hash, error) {
+func getHashHMAC(alg Algorithm) (crypto.Hash, bool) {
 	switch alg {
 	case HS256:
-		return crypto.SHA256, nil
+		return crypto.SHA256, true
 	case HS384:
-		return crypto.SHA384, nil
+		return crypto.SHA384, true
 	case HS512:
-		return crypto.SHA512, nil
+		return crypto.SHA512, true
 	default:
-		return 0, ErrUnsupportedAlg
+		return 0, false
 	}
 }
 
diff --git a/algo_ps.go b/algo_ps.go
index aa712a0..fad3254 100644
--- a/algo_ps.go
+++ b/algo_ps.go
@@ -11,9 +11,9 @@ func NewSignerPS(alg Algorithm, key *rsa.PrivateKey) (Signer, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, opts, err := getParamsPS(alg)
-	if err != nil {
-		return nil, err
+	hash, opts, ok := getParamsPS(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &psAlg{
 		alg:        alg,
@@ -28,9 +28,9 @@ func NewVerifierPS(alg Algorithm, key *rsa.PublicKey) (Verifier, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, opts, err := getParamsPS(alg)
-	if err != nil {
-		return nil, err
+	hash, opts, ok := getParamsPS(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &psAlg{
 		alg:       alg,
@@ -40,16 +40,16 @@ func NewVerifierPS(alg Algorithm, key *rsa.PublicKey) (Verifier, error) {
 	}, nil
 }
 
-func getParamsPS(alg Algorithm) (crypto.Hash, *rsa.PSSOptions, error) {
+func getParamsPS(alg Algorithm) (crypto.Hash, *rsa.PSSOptions, bool) {
 	switch alg {
 	case PS256:
-		return crypto.SHA256, optsPS256, nil
+		return crypto.SHA256, optsPS256, true
 	case PS384:
-		return crypto.SHA384, optsPS384, nil
+		return crypto.SHA384, optsPS384, true
 	case PS512:
-		return crypto.SHA512, optsPS512, nil
+		return crypto.SHA512, optsPS512, true
 	default:
-		return 0, nil, ErrUnsupportedAlg
+		return 0, nil, false
 	}
 }
 
diff --git a/algo_rs.go b/algo_rs.go
index cef7040..1431a85 100644
--- a/algo_rs.go
+++ b/algo_rs.go
@@ -11,9 +11,9 @@ func NewSignerRS(alg Algorithm, key *rsa.PrivateKey) (Signer, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getHashRSA(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getHashRSA(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &rsAlg{
 		alg:        alg,
@@ -27,9 +27,9 @@ func NewVerifierRS(alg Algorithm, key *rsa.PublicKey) (Verifier, error) {
 	if key == nil {
 		return nil, ErrInvalidKey
 	}
-	hash, err := getHashRSA(alg)
-	if err != nil {
-		return nil, err
+	hash, ok := getHashRSA(alg)
+	if !ok {
+		return nil, ErrUnsupportedAlg
 	}
 	return &rsAlg{
 		alg:       alg,
@@ -38,16 +38,16 @@ func NewVerifierRS(alg Algorithm, key *rsa.PublicKey) (Verifier, error) {
 	}, nil
 }
 
-func getHashRSA(alg Algorithm) (crypto.Hash, error) {
+func getHashRSA(alg Algorithm) (crypto.Hash, bool) {
 	switch alg {
 	case RS256:
-		return crypto.SHA256, nil
+		return crypto.SHA256, true
 	case RS384:
-		return crypto.SHA384, nil
+		return crypto.SHA384, true
 	case RS512:
-		return crypto.SHA512, nil
+		return crypto.SHA512, true
 	default:
-		return 0, ErrUnsupportedAlg
+		return 0, false
 	}
 }