return key, ErrCustomerKeyMD5Mismatch
	}
	copy(key[:], clientKey)
	return key, nil
}

// UnsealObjectKey extracts and decrypts the sealed object key
// from the metadata using the SSE-C client key of the HTTP headers
// and returns the decrypted object key.
func (s3 ssec) UnsealObjectKey(h http.Header, metadata map[string]string, bucket, object string) (key ObjectKey, err error) {
	clientKey, err := s3.ParseHTTP(h)

	if _, ok := metadata[MetaSealedKeyS3]; ok {
		return true
	}
	return false
}

// UnsealObjectKey extracts and decrypts the sealed object key
// from the metadata using KMS and returns the decrypted object
// key.
func (s3 sses3) UnsealObjectKey(k *kms.KMS, metadata map[string]string, bucket, object string) (key ObjectKey, err error) {
	if k == nil {
		return key, Errorf("KMS not configured")

	if _, ok := metadata[MetaSealedKeyKMS]; ok {
		return true
	}
	return false
}

// UnsealObjectKey extracts and decrypts the sealed object key
// from the metadata using KMS and returns the decrypted object
// key.
func (s3 ssekms) UnsealObjectKey(k *kms.KMS, metadata map[string]string, bucket, object string) (key ObjectKey, err error) {
	if k == nil {
		return key, Errorf("KMS not configured")

			return nil, errKMSNotConfigured
		}
		objectKey, err := crypto.S3.UnsealObjectKey(GlobalKMS, metadata, bucket, object)
		if err != nil {
			return nil, err
		}
		return objectKey[:], nil
	case crypto.S3KMS:
		if GlobalKMS == nil {
			return nil, errKMSNotConfigured
		}
		objectKey, err := crypto.S3KMS.UnsealObjectKey(GlobalKMS, metadata, bucket, object)
		if err != nil {
			return nil, err
		}

			w.Header().Set(xhttp.AmzServerSideEncryptionKmsContext, kmsCtx)
		}
	case crypto.SSEC:
		// Validate the SSE-C Key set in the header.
		if _, err = crypto.SSEC.UnsealObjectKey(r.Header, objInfo.UserDefined, bucket, object); err != nil {
			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
			return
		}