gmessages/libgm/crypto/cryptor.go
2023-07-12 02:18:14 +03:00

103 lines
2.3 KiB
Go

package crypto
import (
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"errors"
"io"
"google.golang.org/protobuf/proto"
"go.mau.fi/mautrix-gmessages/libgm/binary"
)
type Cryptor struct {
AESKey []byte `json:"aes_key"`
HMACKey []byte `json:"hmac_key"`
}
func NewCryptor(aesKey []byte, hmacKey []byte) *Cryptor {
if aesKey != nil && hmacKey != nil {
return &Cryptor{
AESKey: aesKey,
HMACKey: hmacKey,
}
}
aesKey, hmacKey = GenerateKeys()
return &Cryptor{
AESKey: aesKey,
HMACKey: hmacKey,
}
}
func (c *Cryptor) Encrypt(plaintext []byte) ([]byte, error) {
iv := make([]byte, aes.BlockSize)
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
return nil, err
}
block, err := aes.NewCipher(c.AESKey)
if err != nil {
return nil, err
}
ciphertext := make([]byte, len(plaintext))
stream := cipher.NewCTR(block, iv)
stream.XORKeyStream(ciphertext, plaintext)
ciphertext = append(ciphertext, iv...)
mac := hmac.New(sha256.New, c.HMACKey)
mac.Write(ciphertext)
hmac := mac.Sum(nil)
ciphertext = append(ciphertext, hmac...)
return ciphertext, nil
}
func (c *Cryptor) Decrypt(encryptedData []byte) ([]byte, error) {
if len(encryptedData) < 48 {
return nil, errors.New("input data is too short")
}
hmacSignature := encryptedData[len(encryptedData)-32:]
encryptedDataWithoutHMAC := encryptedData[:len(encryptedData)-32]
mac := hmac.New(sha256.New, c.HMACKey)
mac.Write(encryptedDataWithoutHMAC)
expectedHMAC := mac.Sum(nil)
if !hmac.Equal(hmacSignature, expectedHMAC) {
return nil, errors.New("HMAC mismatch")
}
iv := encryptedDataWithoutHMAC[len(encryptedDataWithoutHMAC)-16:]
encryptedDataWithoutHMAC = encryptedDataWithoutHMAC[:len(encryptedDataWithoutHMAC)-16]
block, err := aes.NewCipher(c.AESKey)
if err != nil {
return nil, err
}
stream := cipher.NewCTR(block, iv)
stream.XORKeyStream(encryptedDataWithoutHMAC, encryptedDataWithoutHMAC)
return encryptedDataWithoutHMAC, nil
}
func (c *Cryptor) EncodeAndEncryptData(message proto.Message) ([]byte, error) {
encodedData, encodeErr := binary.EncodeProtoMessage(message)
if encodeErr != nil {
return nil, encodeErr
}
encryptedData, encryptErr := c.Encrypt(encodedData)
if encryptErr != nil {
return nil, encryptErr
}
return encryptedData, nil
}