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| package main | |
| import ( | |
| "bytes" | |
| "crypto/aes" | |
| "crypto/cipher" | |
| "crypto/rand" | |
| "crypto/rsa" | |
| "crypto/sha256" | |
| "encoding/binary" | |
| "fmt" | |
| "io" | |
| "testing" | |
| ) | |
| func aesEncrypt(key, plaintext []byte) ([]byte, error) { | |
| block, err := aes.NewCipher(key) // key長度有限制必須為16, 24, 32. 對應 AES-128, AES-192, or AES-256 | |
| if err != nil { | |
| return nil, err | |
| } | |
| // 整個密文的長度 = blockSize + len(plaintext) | |
| ciphertext := make([]byte, aes.BlockSize+len(plaintext)) | |
| // 生成block的內容 | |
| iv := ciphertext[:aes.BlockSize] | |
| if _, err = io.ReadFull(rand.Reader, iv); err != nil { | |
| return nil, err | |
| } | |
| stream := cipher.NewCFBEncrypter(block, iv) | |
| stream.XORKeyStream( // 會執行cfb.XORKeyStream, 以plaintext和提供的iv, 計算結果存到ciphertext[aes.BlockSize:]去 | |
| ciphertext[aes.BlockSize:], // 這是輸出。此輸出搭配真實的密鑰，才可以反算回來 | |
| plaintext, | |
| ) | |
| return ciphertext, nil | |
| } | |
| func aesDecrypt(key, ciphertext []byte) ([]byte, error) { | |
| block, err := aes.NewCipher(key) | |
| if err != nil { | |
| return nil, err | |
| } | |
| if len(ciphertext) < aes.BlockSize { | |
| return nil, fmt.Errorf("ciphertext too short") | |
| } | |
| iv := ciphertext[:aes.BlockSize] | |
| ciphertext = ciphertext[aes.BlockSize:] | |
| stream := cipher.NewCFBDecrypter(block, iv) | |
| stream.XORKeyStream(ciphertext, ciphertext) | |
| return ciphertext, nil | |
| } | |
| func GPGEncrypt(data []byte, publicKey *rsa.PublicKey, symmetricKey []byte) ([]byte, error) { | |
| // 使用一個對稱式加密演算法來生成會話的密鑰，假設我們使用AES來加密 | |
| // 被加密起來的訊息 | |
| encryptData, err := aesEncrypt(symmetricKey, data) | |
| if err != nil { | |
| return nil, err | |
| } | |
| // 使用公鑰加密訊息 | |
| iHash := sha256.New() | |
| // 用對方的公鑰對會話密鑰加簽, 對方可以透過此公鑰的對應的私鑰將其還原 | |
| sessionKeyBytes, err := rsa.EncryptOAEP(iHash, rand.Reader, publicKey, symmetricKey, nil) | |
| if err != nil { | |
| return nil, err | |
| } | |
| // 以下只是隨便模擬一個簡單的過程，主要是接收方有辦法識別加簽起來的內容與加簽起來的密鑰 | |
| type Header struct { | |
| DataSize uint32 | |
| KeySize uint32 | |
| } | |
| encryptedMessageBuf := bytes.NewBuffer(nil) | |
| _ = binary.Write(encryptedMessageBuf, binary.BigEndian, &Header{ | |
| DataSize: uint32(len(encryptData)), | |
| KeySize: uint32(len(sessionKeyBytes)), | |
| }) | |
| encryptedMessageBuf.Write(encryptData) | |
| encryptedMessageBuf.Write(sessionKeyBytes) | |
| return encryptedMessageBuf.Bytes(), nil | |
| } | |
| func GPGDecrypt(privateKey *rsa.PrivateKey, encryptedMessage []byte) (orgData []byte, sessionKey []byte, err error) { | |
| // 解析接收的資料內容 | |
| // 這邊只是模擬接收到的資料結構，實際上的資料結構更為複雜 | |
| type ReceiveData struct { | |
| MsgSize uint32 | |
| KeySize uint32 | |
| Msg []byte | |
| Key []byte | |
| } | |
| var msgSize uint32 | |
| msgSize = binary.BigEndian.Uint32(encryptedMessage) // 這是我們自己訂的結構，其一開始4byte表示訊息長度 | |
| var receive ReceiveData | |
| receive.Msg = encryptedMessage[8 : 8+msgSize] // 8為表頭前8byte(msgSize, keySize) | |
| receive.Key = encryptedMessage[8+msgSize:] | |
| // 解出會話用的真實密鑰pairKey | |
| sessionKey, err = rsa.DecryptOAEP(sha256.New(), rand.Reader, // 此為OAEP的特色，對方已經用己方提供的公鑰加密，用自己的私鑰能解密 | |
| privateKey, // 接收方的私鑰理論上只有自己才會有，因此只要沒有這個私鑰，就沒有辦法把會話密鑰還原 | |
| receive.Key, nil, | |
| ) | |
| if err != nil { | |
| return nil, nil, err | |
| } | |
| // 使用會話密鑰將內容還原 | |
| orgData, err = aesDecrypt(sessionKey, receive.Msg) | |
| return orgData, sessionKey, nil | |
| } | |
| func Test_rsaOAEP(t *testing.T) { | |
| // 模擬取得接收方的公鑰 | |
| receiverKey, err := rsa.GenerateKey(rand.Reader, 2048) | |
| if err != nil { | |
| t.Fatal(err) | |
| } | |
| receiverPublicKey := &receiverKey.PublicKey | |
| // 加簽過程: 用公鑰加密 | |
| realMessage := []byte("這是一個秘密訊息") | |
| // 模擬隨機生成對稱式密鑰 | |
| const defaultKeySize = 16 // 由於我們採用AES演算法，他的私鑰長度有限制，對應的長度分別為16, 24, 32對應AES-128, AES-192, or AES-256. | |
| symmetricKey := make([]byte, defaultKeySize) | |
| if _, err = rand.Read(symmetricKey); err != nil { | |
| t.Fatal(err) | |
| } | |
| encryptedMessage, err := GPGEncrypt(realMessage, receiverPublicKey, symmetricKey) | |
| if err != nil { | |
| t.Fatal(err) | |
| } | |
| expectedMsg, symmetricKey2, err := GPGDecrypt(receiverKey, encryptedMessage) | |
| if err != nil { | |
| t.Fatal(err) | |
| } | |
| // 驗證 | |
| if !bytes.Equal(symmetricKey, symmetricKey2) { | |
| t.Fatal("密鑰不同", err) | |
| } | |
| if !bytes.Equal(expectedMsg, realMessage) { | |
| t.Fatal("內容不一致") | |
| } | |
| } |
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