introduce new package pkg/kms (#12019)

This commit introduces a new package `pkg/kms`.
It contains basic types and functions to interact
with various KMS implementations.

This commit also moves KMS-related code from `cmd/crypto`
to `pkg/kms`. Now, it is possible to implement a KMS-based
config data encryption in the `pkg/config` package.

pkg/kms/single-key_test.go

@@ -0,0 +1,84 @@
+// MinIO Cloud Storage, (C) 2021 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 kms
+
+import (
+	"bytes"
+	"encoding/base64"
+	"testing"
+)
+
+func TestSingleKeyRoundtrip(t *testing.T) {
+	KMS, err := Parse("my-key:eEm+JI9/q4JhH8QwKvf3LKo4DEBl6QbfvAl1CAbMIv8=")
+	if err != nil {
+		t.Fatalf("Failed to initialize KMS: %v", err)
+	}
+
+	key, err := KMS.GenerateKey("my-key", Context{})
+	if err != nil {
+		t.Fatalf("Failed to generate key: %v", err)
+	}
+	plaintext, err := KMS.DecryptKey(key.KeyID, key.Ciphertext, Context{})
+	if err != nil {
+		t.Fatalf("Failed to decrypt key: %v", err)
+	}
+	if !bytes.Equal(key.Plaintext, plaintext) {
+		t.Fatalf("Decrypted key does not match generated one: got %x - want %x", key.Plaintext, plaintext)
+	}
+}
+
+func TestDecryptKey(t *testing.T) {
+	KMS, err := Parse("my-key:eEm+JI9/q4JhH8QwKvf3LKo4DEBl6QbfvAl1CAbMIv8=")
+	if err != nil {
+		t.Fatalf("Failed to initialize KMS: %v", err)
+	}
+
+	for i, test := range decryptKeyTests {
+		dataKey, err := base64.StdEncoding.DecodeString(test.Plaintext)
+		if err != nil {
+			t.Fatalf("Test %d: failed to decode plaintext key: %v", i, err)
+		}
+		ciphertext, err := base64.StdEncoding.DecodeString(test.Ciphertext)
+		if err != nil {
+			t.Fatalf("Test %d: failed to decode ciphertext key: %v", i, err)
+		}
+		plaintext, err := KMS.DecryptKey(test.KeyID, ciphertext, test.Context)
+		if err != nil {
+			t.Fatalf("Test %d: failed to decrypt key: %v", i, err)
+		}
+		if !bytes.Equal(plaintext, dataKey) {
+			t.Fatalf("Test %d: decrypted key does not generated one: got %x - want %x", i, plaintext, dataKey)
+		}
+	}
+}
+
+var decryptKeyTests = []struct {
+	KeyID      string
+	Plaintext  string
+	Ciphertext string
+	Context    Context
+}{
+	{
+		KeyID:      "my-key",
+		Plaintext:  "zmS7NrG765UZ0ZN85oPjybelxqVvpz01vxsSpOISy2M=",
+		Ciphertext: "eyJhZWFkIjoiQ2hhQ2hhMjBQb2x5MTMwNSIsIml2IjoiSmJJK3Z3dll3dzFsQ2I1VnBrQUZ1UT09Iiwibm9uY2UiOiJBUmpJakp4QlNENTQxR3o4IiwiYnl0ZXMiOiJLQ2JFYzJzQTBUTHZBN2FXVFdhMjNBZGNjVmZKTXBPeHdnRzhobSs0UGFOcnhZZnkxeEZXWmcyZ0VlblZyT2d2In0=",
+	},
+	{
+		KeyID:      "my-key",
+		Plaintext:  "UnPWsZgVI+T4L9WGNzFlP1PsP1Z6hn2Fx8ISeZfDGnA=",
+		Ciphertext: "eyJhZWFkIjoiQ2hhQ2hhMjBQb2x5MTMwNSIsIml2IjoicjQreWZpVmJWSVlSMFoySTlGcSs2Zz09Iiwibm9uY2UiOiIyWXB3R3dFNTlHY1ZyYUkzIiwiYnl0ZXMiOiJrL3N2TWdsT1U3L0tnd3Y3M2hlRzM4TldXNTc1WExjRnAzU2F4UUhETWpKR1l5UkkzRml5Z3UyT2V1dEdQWE5MIn0=",
+		Context:    Context{"key": "value"},
+	},
+}