return AWS S3 compatible error for invalid but equal keys during key rotation (#5783)

This change let the server return the S3 error for a key rotation
if the source key is not valid but equal to the destination key.

This change also fixes the SSE-C error messages since AWS returns error messages
ending with a '.'.

Fixes #5625

cmd/api-errors.go

@@ -138,6 +138,7 @@ const (
 	ErrMissingSSECustomerKey
 	ErrMissingSSECustomerKeyMD5
 	ErrSSECustomerKeyMD5Mismatch
+	ErrInvalidSSECustomerParameters
 
 	// Bucket notification related errors.
 	ErrEventNotification
@@ -629,7 +630,7 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 	},
 	ErrInsecureSSECustomerRequest: {
 		Code:           "InvalidRequest",
-		Description:    errInsecureSSERequest.Error(),
+		Description:    "Requests specifying Server Side Encryption with Customer provided keys must be made over a secure connection.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrSSEMultipartEncrypted: {
@@ -639,7 +640,7 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 	},
 	ErrSSEEncryptedObject: {
 		Code:           "InvalidRequest",
-		Description:    errEncryptedObject.Error(),
+		Description:    "The object was stored using a form of Server Side Encryption. The correct parameters must be provided to retrieve the object.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrInvalidEncryptionParameters: {
@@ -649,27 +650,32 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 	},
 	ErrInvalidSSECustomerAlgorithm: {
 		Code:           "InvalidArgument",
-		Description:    errInvalidSSEAlgorithm.Error(),
+		Description:    "Requests specifying Server Side Encryption with Customer provided keys must provide a valid encryption algorithm.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrInvalidSSECustomerKey: {
 		Code:           "InvalidArgument",
-		Description:    errInvalidSSEKey.Error(),
+		Description:    "The secret key was invalid for the specified algorithm.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrMissingSSECustomerKey: {
 		Code:           "InvalidArgument",
-		Description:    errMissingSSEKey.Error(),
+		Description:    "Requests specifying Server Side Encryption with Customer provided keys must provide an appropriate secret key.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrMissingSSECustomerKeyMD5: {
 		Code:           "InvalidArgument",
-		Description:    errMissingSSEKeyMD5.Error(),
+		Description:    "Requests specifying Server Side Encryption with Customer provided keys must provide the client calculated MD5 of the secret key.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrSSECustomerKeyMD5Mismatch: {
 		Code:           "InvalidArgument",
-		Description:    errSSEKeyMD5Mismatch.Error(),
+		Description:    "The calculated MD5 hash of the key did not match the hash that was provided.",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
+	ErrInvalidSSECustomerParameters: {
+		Code:           "InvalidArgument",
+		Description:    "The provided encryption parameters did not match the ones used originally.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 
@@ -884,6 +890,8 @@ func toAPIErrorCode(err error) (apiErr APIErrorCode) {
 		return ErrObjectTampered
 	case errEncryptedObject:
 		return ErrSSEEncryptedObject
+	case errInvalidSSEParameters:
+		return ErrInvalidSSECustomerParameters
 	case errSSEKeyMismatch:
 		return ErrAccessDenied // no access without correct key
 	}

cmd/encryption-v1.go

@@ -35,14 +35,15 @@ import (
 
 var (
 	// AWS errors for invalid SSE-C requests.
-	errInsecureSSERequest  = errors.New("Requests specifying Server Side Encryption with Customer provided keys must be made over a secure connection")
-	errEncryptedObject     = errors.New("The object was stored using a form of Server Side Encryption. The correct parameters must be provided to retrieve the object")
-	errInvalidSSEAlgorithm = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide a valid encryption algorithm")
-	errMissingSSEKey       = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide an appropriate secret key")
-	errInvalidSSEKey       = errors.New("The secret key was invalid for the specified algorithm")
-	errMissingSSEKeyMD5    = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide the client calculated MD5 of the secret key")
-	errSSEKeyMD5Mismatch   = errors.New("The calculated MD5 hash of the key did not match the hash that was provided")
-	errSSEKeyMismatch      = errors.New("The client provided key does not match the key provided when the object was encrypted") // this msg is not shown to the client
+	errInsecureSSERequest   = errors.New("SSE-C requests require TLS connections")
+	errEncryptedObject      = errors.New("The object was stored using a form of SSE")
+	errInvalidSSEAlgorithm  = errors.New("The SSE-C algorithm is not valid")
+	errMissingSSEKey        = errors.New("The SSE-C request is missing the customer key")
+	errInvalidSSEKey        = errors.New("The SSE-C key is invalid")
+	errMissingSSEKeyMD5     = errors.New("The SSE-C request is missing the customer key MD5")
+	errSSEKeyMD5Mismatch    = errors.New("The key MD5 does not match the SSE-C key")
+	errSSEKeyMismatch       = errors.New("The SSE-C key is not correct")                  // access denied
+	errInvalidSSEParameters = errors.New("The SSE-C key for key-rotation is not correct") // special access denied
 
 	// Additional Minio errors for SSE-C requests.
 	errObjectTampered = errors.New("The requested object was modified and may be compromised")
@@ -247,9 +248,6 @@ func ParseSSECustomerHeader(header http.Header) (key []byte, err error) {
 
 // This function rotates old to new key.
 func rotateKey(oldKey []byte, newKey []byte, metadata map[string]string) error {
-	if subtle.ConstantTimeCompare(oldKey, newKey) == 1 {
-		return nil
-	}
 	delete(metadata, SSECustomerKey) // make sure we do not save the key by accident
 
 	if metadata[ServerSideEncryptionSealAlgorithm] != SSESealAlgorithmDareSha256 { // currently DARE-SHA256 is the only option
@@ -273,10 +271,14 @@ func rotateKey(oldKey []byte, newKey []byte, metadata map[string]string) error {
 	n, err := sio.Decrypt(objectEncryptionKey, bytes.NewReader(sealedKey), sio.Config{
 		Key: keyEncryptionKey,
 	})
-	if n != 32 || err != nil {
-		// Either the provided key does not match or the object was tampered.
-		// To provide strict AWS S3 compatibility we return: access denied.
-		return errSSEKeyMismatch
+	if n != 32 || err != nil { // Either the provided key does not match or the object was tampered.
+		if subtle.ConstantTimeCompare(oldKey, newKey) == 1 {
+			return errInvalidSSEParameters // AWS returns special error for equal but invalid keys.
+		}
+		return errSSEKeyMismatch // To provide strict AWS S3 compatibility we return: access denied.
+	}
+	if subtle.ConstantTimeCompare(oldKey, newKey) == 1 {
+		return nil // we don't need to rotate keys if newKey == oldKey
 	}
 
 	nonce := make([]byte, 32) // generate random values for key derivation