make the crypto error type a native go type (#8267)

This commit makes the `crypto.Error` type a native go (string)
type. That allows us to define error values as constants instead
of variables.

For reference see:
 - https://twitter.com/_aead_/status/1118170258215514115?s=20
 - https://dave.cheney.net/2016/04/07/constant-errors

cmd/api-errors.go

@@ -1723,6 +1723,12 @@ func toAPIError(ctx context.Context, err error) APIError {
 		// their internal error types. This code is only
 		// useful with gateway implementations.
 		switch e := err.(type) {
+		case crypto.Error:
+			apiErr = APIError{
+				Code:           "XKMSInternalError",
+				Description:    e.Error(),
+				HTTPStatusCode: http.StatusBadRequest,
+			}
 		case minio.ErrorResponse:
 			apiErr = APIError{
 				Code:           e.Code,

cmd/crypto/error.go

@@ -19,9 +19,9 @@ import "errors"
 // Error is the generic type for any error happening during decrypting
 // an object. It indicates that the object itself or its metadata was
 // modified accidentally or maliciously.
-type Error struct{ msg string }
+type Error string
 
-func (e Error) Error() string { return e.msg }
+func (e Error) Error() string { return string(e) }
 
 var (
 	// ErrInvalidEncryptionMethod indicates that the specified SSE encryption method
@@ -56,14 +56,14 @@ var (
 	ErrIncompatibleEncryptionMethod = errors.New("Server side encryption specified with both SSE-C and SSE-S3 headers")
 )
 
-var (
-	errMissingInternalIV            = Error{"The object metadata is missing the internal encryption IV"}
-	errMissingInternalSealAlgorithm = Error{"The object metadata is missing the internal seal algorithm"}
+const (
+	errMissingInternalIV            Error = "The object metadata is missing the internal encryption IV"
+	errMissingInternalSealAlgorithm Error = "The object metadata is missing the internal seal algorithm"
 
-	errInvalidInternalIV            = Error{"The internal encryption IV is malformed"}
-	errInvalidInternalSealAlgorithm = Error{"The internal seal algorithm is invalid and not supported"}
+	errInvalidInternalIV            Error = "The internal encryption IV is malformed"
+	errInvalidInternalSealAlgorithm Error = "The internal seal algorithm is invalid and not supported"
 
-	errMissingUpdatedKey = Error{"The key update returned no error but also no sealed key"}
+	errMissingUpdatedKey Error = "The key update returned no error but also no sealed key"
 )
 
 var (

cmd/crypto/key.go

@@ -108,7 +108,7 @@ func (key *ObjectKey) Unseal(extKey [32]byte, sealedKey SealedKey, domain, bucke
 	)
 	switch sealedKey.Algorithm {
 	default:
-		return Error{fmt.Sprintf("The sealing algorithm '%s' is not supported", sealedKey.Algorithm)}
+		return Error(fmt.Sprintf("The sealing algorithm '%s' is not supported", sealedKey.Algorithm))
 	case SealAlgorithm:
 		mac := hmac.New(sha256.New, extKey[:])
 		mac.Write(sealedKey.IV[:])

cmd/crypto/metadata.go

@@ -172,7 +172,7 @@ func (s3) ParseMetadata(metadata map[string]string) (keyID string, kmsKey []byte
 	}
 	b64SealedKey, ok := metadata[S3SealedKey]
 	if !ok {
-		return keyID, kmsKey, sealedKey, Error{"The object metadata is missing the internal sealed key for SSE-S3"}
+		return keyID, kmsKey, sealedKey, Error("The object metadata is missing the internal sealed key for SSE-S3")
 	}
 
 	// There are two possibilites:
@@ -182,10 +182,10 @@ func (s3) ParseMetadata(metadata map[string]string) (keyID string, kmsKey []byte
 	keyID, idPresent := metadata[S3KMSKeyID]
 	b64KMSSealedKey, kmsKeyPresent := metadata[S3KMSSealedKey]
 	if !idPresent && kmsKeyPresent {
-		return keyID, kmsKey, sealedKey, Error{"The object metadata is missing the internal KMS key-ID for SSE-S3"}
+		return keyID, kmsKey, sealedKey, Error("The object metadata is missing the internal KMS key-ID for SSE-S3")
 	}
 	if idPresent && !kmsKeyPresent {
-		return keyID, kmsKey, sealedKey, Error{"The object metadata is missing the internal sealed KMS data key for SSE-S3"}
+		return keyID, kmsKey, sealedKey, Error("The object metadata is missing the internal sealed KMS data key for SSE-S3")
 	}
 
 	// Check whether all extracted values are well-formed
@@ -198,12 +198,12 @@ func (s3) ParseMetadata(metadata map[string]string) (keyID string, kmsKey []byte
 	}
 	encryptedKey, err := base64.StdEncoding.DecodeString(b64SealedKey)
 	if err != nil || len(encryptedKey) != 64 {
-		return keyID, kmsKey, sealedKey, Error{"The internal sealed key for SSE-S3 is invalid"}
+		return keyID, kmsKey, sealedKey, Error("The internal sealed key for SSE-S3 is invalid")
 	}
 	if idPresent && kmsKeyPresent { // We are using a KMS -> parse the sealed KMS data key.
 		kmsKey, err = base64.StdEncoding.DecodeString(b64KMSSealedKey)
 		if err != nil {
-			return keyID, kmsKey, sealedKey, Error{"The internal sealed KMS data key for SSE-S3 is invalid"}
+			return keyID, kmsKey, sealedKey, Error("The internal sealed KMS data key for SSE-S3 is invalid")
 		}
 	}
 
@@ -244,7 +244,7 @@ func (ssec) ParseMetadata(metadata map[string]string) (sealedKey SealedKey, err
 	}
 	b64SealedKey, ok := metadata[SSECSealedKey]
 	if !ok {
-		return sealedKey, Error{"The object metadata is missing the internal sealed key for SSE-C"}
+		return sealedKey, Error("The object metadata is missing the internal sealed key for SSE-C")
 	}
 
 	// Check whether all extracted values are well-formed
@@ -257,7 +257,7 @@ func (ssec) ParseMetadata(metadata map[string]string) (sealedKey SealedKey, err
 	}
 	encryptedKey, err := base64.StdEncoding.DecodeString(b64SealedKey)
 	if err != nil || len(encryptedKey) != 64 {
-		return sealedKey, Error{"The internal sealed key for SSE-C is invalid"}
+		return sealedKey, Error("The internal sealed key for SSE-C is invalid")
 	}
 
 	sealedKey.Algorithm = algorithm

cmd/crypto/metadata_test.go

@@ -125,15 +125,15 @@ var s3ParseMetadataTests = []struct {
 		DataKey: []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 1
 	{
-		ExpectedErr: Error{"The object metadata is missing the internal sealed key for SSE-S3"},
+		ExpectedErr: Error("The object metadata is missing the internal sealed key for SSE-S3"),
 		Metadata:    map[string]string{SSEIV: "", SSESealAlgorithm: ""}, DataKey: []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 2
 	{
-		ExpectedErr: Error{"The object metadata is missing the internal KMS key-ID for SSE-S3"},
+		ExpectedErr: Error("The object metadata is missing the internal KMS key-ID for SSE-S3"),
 		Metadata:    map[string]string{SSEIV: "", SSESealAlgorithm: "", S3SealedKey: "", S3KMSSealedKey: "IAAF0b=="}, DataKey: []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 3
 	{
-		ExpectedErr: Error{"The object metadata is missing the internal sealed KMS data key for SSE-S3"},
+		ExpectedErr: Error("The object metadata is missing the internal sealed KMS data key for SSE-S3"),
 		Metadata:    map[string]string{SSEIV: "", SSESealAlgorithm: "", S3SealedKey: "", S3KMSKeyID: ""},
 		DataKey:     []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 4
@@ -150,7 +150,7 @@ var s3ParseMetadataTests = []struct {
 		DataKey: []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 6
 	{
-		ExpectedErr: Error{"The internal sealed key for SSE-S3 is invalid"},
+		ExpectedErr: Error("The internal sealed key for SSE-S3 is invalid"),
 		Metadata: map[string]string{
 			SSEIV: base64.StdEncoding.EncodeToString(make([]byte, 32)), SSESealAlgorithm: SealAlgorithm, S3SealedKey: "",
 			S3KMSKeyID: "", S3KMSSealedKey: "",
@@ -158,7 +158,7 @@ var s3ParseMetadataTests = []struct {
 		DataKey: []byte{}, KeyID: "", SealedKey: SealedKey{},
 	}, // 7
 	{
-		ExpectedErr: Error{"The internal sealed KMS data key for SSE-S3 is invalid"},
+		ExpectedErr: Error("The internal sealed KMS data key for SSE-S3 is invalid"),
 		Metadata: map[string]string{
 			SSEIV: base64.StdEncoding.EncodeToString(make([]byte, 32)), SSESealAlgorithm: SealAlgorithm,
 			S3SealedKey: base64.StdEncoding.EncodeToString(make([]byte, 64)), S3KMSKeyID: "key-1",
@@ -218,7 +218,7 @@ var ssecParseMetadataTests = []struct {
 	{ExpectedErr: errMissingInternalIV, Metadata: map[string]string{}, SealedKey: SealedKey{}},                     // 0
 	{ExpectedErr: errMissingInternalSealAlgorithm, Metadata: map[string]string{SSEIV: ""}, SealedKey: SealedKey{}}, // 1
 	{
-		ExpectedErr: Error{"The object metadata is missing the internal sealed key for SSE-C"},
+		ExpectedErr: Error("The object metadata is missing the internal sealed key for SSE-C"),
 		Metadata:    map[string]string{SSEIV: "", SSESealAlgorithm: ""}, SealedKey: SealedKey{},
 	}, // 2
 	{
@@ -233,7 +233,7 @@ var ssecParseMetadataTests = []struct {
 		SealedKey: SealedKey{},
 	}, // 4
 	{
-		ExpectedErr: Error{"The internal sealed key for SSE-C is invalid"},
+		ExpectedErr: Error("The internal sealed key for SSE-C is invalid"),
 		Metadata: map[string]string{
 			SSEIV: base64.StdEncoding.EncodeToString(make([]byte, 32)), SSESealAlgorithm: SealAlgorithm, SSECSealedKey: "",
 		},