AB#1943 Extract KMS package (#56)

* Extract kmsapi from coordinator

* Add kmsapi cmd server

kms/server/kmsapi/kmsapi_test.go

@@ -0,0 +1,58 @@
+package kmsapi
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/edgelesssys/constellation/kms/server/kmsapi/kmsproto"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zaptest"
+)
+
+func TestGetDataKey(t *testing.T) {
+	assert := assert.New(t)
+	require := require.New(t)
+
+	kms := &stubKMS{derivedKey: []byte{0x0, 0x1, 0x2, 0x3, 0x4, 0x5}}
+	api := New(zaptest.NewLogger(t), kms)
+
+	res, err := api.GetDataKey(context.Background(), &kmsproto.GetDataKeyRequest{DataKeyId: "1", Length: 32})
+	require.NoError(err)
+	assert.Equal(kms.derivedKey, res.DataKey)
+
+	// Test no data key id
+	res, err = api.GetDataKey(context.Background(), &kmsproto.GetDataKeyRequest{Length: 32})
+	require.Error(err)
+	assert.Nil(res)
+
+	// Test no / zero key length
+	res, err = api.GetDataKey(context.Background(), &kmsproto.GetDataKeyRequest{DataKeyId: "1"})
+	require.Error(err)
+	assert.Nil(res)
+
+	// Test derive key error
+	api = New(zaptest.NewLogger(t), &stubKMS{deriveKeyErr: errors.New("error")})
+	res, err = api.GetDataKey(context.Background(), &kmsproto.GetDataKeyRequest{DataKeyId: "1", Length: 32})
+	assert.Error(err)
+	assert.Nil(res)
+}
+
+type stubKMS struct {
+	masterKey    []byte
+	derivedKey   []byte
+	deriveKeyErr error
+}
+
+func (c *stubKMS) CreateKEK(ctx context.Context, keyID string, kek []byte) error {
+	c.masterKey = kek
+	return nil
+}
+
+func (c *stubKMS) GetDEK(ctx context.Context, kekID string, dekID string, dekSize int) ([]byte, error) {
+	if c.deriveKeyErr != nil {
+		return nil, c.deriveKeyErr
+	}
+	return c.derivedKey, nil
+}