// 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 (

"bytes"

"context"

"crypto/hmac"

"crypto/rand"

"errors"

"fmt"

"io"

"sort"

"github.com/minio/minio/cmd/logger"

sha256 "github.com/minio/sha256-simd"

"github.com/minio/sio"

)

// Context is a list of key-value pairs cryptographically

// associated with a certain object.

type Context map[string]string

// WriteTo writes the context in a canonical from to w.

// It returns the number of bytes and the first error

// encounter during writing to w, if any.

//

// WriteTo sorts the context keys and writes the sorted

// key-value pairs as canonical JSON object to w.

func (c Context) WriteTo(w io.Writer) (n int64, err error) {

sortedKeys := make(sort.StringSlice, 0, len(c))

for k := range c {

sortedKeys = append(sortedKeys, k)

}

sort.Sort(sortedKeys)

nn, err := io.WriteString(w, "{")

if err != nil {

return n + int64(nn), err

}

n += int64(nn)

for i, k := range sortedKeys {

s := fmt.Sprintf("\"%s\":\"%s\",", k, c[k])

if i == len(sortedKeys)-1 {

s = s[:len(s)-1] // remove last ','

}

nn, err = io.WriteString(w, s)

if err != nil {

return n + int64(nn), err

}

n += int64(nn)

}

nn, err = io.WriteString(w, "}")

return n + int64(nn), err

}

// KMS represents an active and authenticted connection

// to a Key-Management-Service. It supports generating

// data key generation and unsealing of KMS-generated

// data keys.

type KMS interface {

// GenerateKey generates a new random data key using

// the master key referenced by the keyID. It returns

// the plaintext key and the sealed plaintext key

// on success.

//

// The context is cryptographically bound to the

// generated key. The same context must be provided

// again to unseal the generated key.

GenerateKey(keyID string, context Context) (key [32]byte, sealedKey []byte, err error)

// UnsealKey unseals the sealedKey using the master key

// referenced by the keyID. The provided context must

// match the context used to generate the sealed key.

UnsealKey(keyID string, sealedKey []byte, context Context) (key [32]byte, err error)

}

type masterKeyKMS struct {

masterKey [32]byte

}

// NewKMS returns a basic KMS implementation from a single 256 bit master key.

//

// The KMS accepts any keyID but binds the keyID and context cryptographically

// to the generated keys.

func NewKMS(key [32]byte) KMS { return &masterKeyKMS{masterKey: key} }

func (kms *masterKeyKMS) GenerateKey(keyID string, ctx Context) (key [32]byte, sealedKey []byte, err error) {

if _, err = io.ReadFull(rand.Reader, key[:]); err != nil {

logger.CriticalIf(context.Background(), errOutOfEntropy)

}

var (

buffer bytes.Buffer

derivedKey = kms.deriveKey(keyID, ctx)

)

if n, err := sio.Encrypt(&buffer, bytes.NewReader(key[:]), sio.Config{Key: derivedKey[:]}); err != nil || n != 64 {

logger.CriticalIf(context.Background(), errors.New("KMS: unable to encrypt data key"))

}

sealedKey = buffer.Bytes()

return key, sealedKey, nil

}

func (kms *masterKeyKMS) UnsealKey(keyID string, sealedKey []byte, ctx Context) (key [32]byte, err error) {

var (

buffer bytes.Buffer

derivedKey = kms.deriveKey(keyID, ctx)

)

if n, err := sio.Decrypt(&buffer, bytes.NewReader(sealedKey), sio.Config{Key: derivedKey[:]}); err != nil || n != 32 {

return key, err // TODO(aead): upgrade sio to use sio.Error

}

copy(key[:], buffer.Bytes())

return key, nil

}

func (kms *masterKeyKMS) deriveKey(keyID string, context Context) (key [32]byte) {

if context == nil {

context = Context{}

}

mac := hmac.New(sha256.New, kms.masterKey[:])

mac.Write([]byte(keyID))

context.WriteTo(mac)

mac.Sum(key[:0])

return key

}