new package: cmd/crypto (#6062)

This commit introduces a new crypto package providing
AWS S3 related cryptographic building blocks to implement
SSE-S3 (master key or KMS) and SSE-C.

This change only adds some basic functionallity esp.
related to SSE-S3 and documents the general approach
for SSE-S3 and SSE-C.

cmd/crypto/header_test.go

@@ -0,0 +1,56 @@
+// Minio Cloud Storage, (C) 2015, 2016, 2017, 2018 Minio, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package crypto
+
+import (
+	"net/http"
+	"testing"
+)
+
+var isRequestedTests = []struct {
+	Header   http.Header
+	Expected bool
+}{
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{"AES256"}}, Expected: true},  // 0
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{"AES-256"}}, Expected: true}, // 1
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{""}}, Expected: true},        // 2
+	{Header: http.Header{"X-Amz-Server-Side-Encryptio": []string{"AES256"}}, Expected: false},  // 3
+}
+
+func TestS3IsRequested(t *testing.T) {
+	for i, test := range isRequestedTests {
+		if got := S3.IsRequested(test.Header); got != test.Expected {
+			t.Errorf("Test %d: Wanted %v but got %v", i, test.Expected, got)
+		}
+	}
+}
+
+var parseTests = []struct {
+	Header      http.Header
+	ExpectedErr error
+}{
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{"AES256"}}, ExpectedErr: nil},                         // 0
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{"AES-256"}}, ExpectedErr: ErrInvalidEncryptionMethod}, // 1
+	{Header: http.Header{"X-Amz-Server-Side-Encryption": []string{""}}, ExpectedErr: ErrInvalidEncryptionMethod},        // 2
+	{Header: http.Header{"X-Amz-Server-Side-Encryptio": []string{"AES256"}}, ExpectedErr: ErrInvalidEncryptionMethod},   // 3
+}
+
+func TestS3Parse(t *testing.T) {
+	for i, test := range parseTests {
+		if err := S3.Parse(test.Header); err != test.ExpectedErr {
+			t.Errorf("Test %d: Wanted '%v' but got '%v'", i, test.ExpectedErr, err)
+		}
+	}
+}