Consolidate API names related to Key

algorithm.go

@@ -43,8 +43,8 @@ const (
 	// PureEdDSA by RFC 8152.
 	AlgorithmEdDSA Algorithm = -8
 
-	// An invalid/unrecognised algorithm.
-	AlgorithmInvalid Algorithm = 0
+	// Reserved value.
+	AlgorithmReserved Algorithm = 0
 )
 
 // Algorithm represents an IANA algorithm entry in the COSE Algorithms registry.
@@ -75,6 +75,8 @@ func (a Algorithm) String() string {
 		// As stated in RFC 8152 8.2, only the pure EdDSA version is used for
 		// COSE.
 		return "EdDSA"
+	case AlgorithmReserved:
+		return "Reserved"
 	default:
 		return "unknown algorithm value " + strconv.Itoa(int(a))
 	}

algorithm_test.go

@@ -12,18 +12,21 @@ import (
 func TestAlgorithm_String(t *testing.T) {
 	// run tests
 	tests := []struct {
-		name string
 		alg  Algorithm
 		want string
 	}{
-		{
-			name: "unknown algorithm",
-			alg:  0,
-			want: "unknown algorithm value 0",
-		},
+		{AlgorithmPS256, "PS256"},
+		{AlgorithmPS384, "PS384"},
+		{AlgorithmPS512, "PS512"},
+		{AlgorithmES256, "ES256"},
+		{AlgorithmES384, "ES384"},
+		{AlgorithmES512, "ES512"},
+		{AlgorithmEdDSA, "EdDSA"},
+		{AlgorithmReserved, "Reserved"},
+		{7, "unknown algorithm value 7"},
 	}
 	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
+		t.Run(tt.want, func(t *testing.T) {
 			if got := tt.alg.String(); got != tt.want {
 				t.Errorf("Algorithm.String() = %v, want %v", got, tt.want)
 			}

headers.go

@@ -119,9 +119,9 @@ func (h ProtectedHeader) Algorithm() (Algorithm, error) {
 	case int64:
 		return Algorithm(alg), nil
 	case string:
-		return AlgorithmInvalid, fmt.Errorf("unknown algorithm value %q", alg)
+		return AlgorithmReserved, fmt.Errorf("unknown algorithm value %q", alg)
 	default:
-		return AlgorithmInvalid, ErrInvalidAlgorithm
+		return AlgorithmReserved, ErrInvalidAlgorithm
 	}
 }