micro/tunnel/crypto.go

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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)
}
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// 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
}
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// 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()
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if len(data) < nonceSize {
return nil, ErrDecryptingData
}
// 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
}