package tunnel import ( "crypto/aes" "crypto/cipher" "crypto/rand" "crypto/sha256" "io" ) // hash hahes the data into 32 bytes key and returns it // hash uses sha256 underneath to hash the supplied key func hash(key string) []byte { hasher := sha256.New() hasher.Write([]byte(key)) return hasher.Sum(nil) } // Encrypt encrypts data and returns the encrypted data func Encrypt(data []byte, key string) ([]byte, error) { // generate a new AES cipher using our 32 byte key c, err := aes.NewCipher(hash(key)) if err != nil { return nil, err } // gcm or Galois/Counter Mode, is a mode of operation // for symmetric key cryptographic block ciphers // - https://en.wikipedia.org/wiki/Galois/Counter_Mode gcm, err := cipher.NewGCM(c) if err != nil { return nil, err } // create a new byte array the size of the nonce // NOTE: we might use smaller nonce size in the future nonce := make([]byte, gcm.NonceSize()) if _, err = io.ReadFull(rand.Reader, nonce); err != nil { return nil, err } // NOTE: we prepend the nonce to the payload // we need to do this as we need the same nonce // to decrypt the payload when receiving it return gcm.Seal(nonce, nonce, data, nil), nil } // Decrypt decrypts the payload and returns the decrypted data func Decrypt(data []byte, key string) ([]byte, error) { // generate AES cipher for decrypting the message c, err := aes.NewCipher(hash(key)) if err != nil { return nil, err } // we use GCM to encrypt the payload gcm, err := cipher.NewGCM(c) if err != nil { return nil, err } nonceSize := gcm.NonceSize() // NOTE: we need to parse out nonce from the payload // we prepend the nonce to every encrypted payload nonce, ciphertext := data[:nonceSize], data[nonceSize:] plaintext, err := gcm.Open(nil, nonce, ciphertext, nil) if err != nil { return nil, err } return plaintext, nil }