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// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
package crypto
import (
"crypto/aes"
"crypto/cipher"
"crypto/ecdh"
"crypto/rand"
"crypto/sha256"
"encoding/json"
"fmt"
"strconv"
"strings"
"time"
"github.com/kovidgoyal/kitty/tools/utils"
"github.com/kovidgoyal/kitty/tools/utils/base85"
)
func curve25519_key_pair() (private_key []byte, public_key []byte, err error) {
curve := ecdh.X25519()
privkey, err := curve.GenerateKey(rand.Reader)
if err == nil {
pubkey := privkey.PublicKey()
return privkey.Bytes(), pubkey.Bytes(), nil
}
return nil, nil, err
}
func curve25519_derive_shared_secret(private_key []byte, public_key []byte) (secret []byte, err error) {
prkey, err := ecdh.X25519().NewPrivateKey(private_key)
if err != nil {
return nil, fmt.Errorf("Invalid X25519 private key: %w", err)
}
pubkey, err := ecdh.X25519().NewPublicKey(public_key)
if err != nil {
return nil, fmt.Errorf("Invalid X25519 public key: %w", err)
}
secret, err = prkey.ECDH(pubkey)
if err != nil {
err = fmt.Errorf("Failed to perform ECDH shared secret derivation: %w", err)
}
return
}
func b85_encode(data []byte) (encoded string) {
encoded = base85.EncodeToString(data)
return
}
func b85_decode(data string) (decoded []byte, err error) {
decoded, err = base85.DecodeString(data)
return
}
func encrypt(plaintext []byte, alice_public_key []byte, encryption_protocol string) (iv []byte, tag []byte, ciphertext []byte, bob_public_key []byte, err error) {
bob_private_key, bob_public_key, err := KeyPair(encryption_protocol)
if err != nil {
return
}
shared_secret_raw, err := curve25519_derive_shared_secret(bob_private_key, alice_public_key)
if err != nil {
return
}
shared_secret_hashed := sha256.Sum256(shared_secret_raw)
shared_secret := shared_secret_hashed[:]
block, err := aes.NewCipher(shared_secret)
if err != nil {
return
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
return
}
iv = make([]byte, aesgcm.NonceSize())
_, err = rand.Read(iv)
if err != nil {
return
}
output := aesgcm.Seal(nil, iv, plaintext, nil)
ciphertext = output[0 : len(output)-16]
tag = output[len(output)-16:]
return
}
func KeyPair(encryption_protocol string) (private_key []byte, public_key []byte, err error) {
switch encryption_protocol {
case "1":
return curve25519_key_pair()
default:
err = fmt.Errorf("Unknown encryption protocol: %s", encryption_protocol)
return
}
}
func EncodePublicKey(pubkey []byte, encryption_protocol string) (ans string, err error) {
switch encryption_protocol {
case "1":
ans = fmt.Sprintf("1:%s", b85_encode(pubkey))
default:
err = fmt.Errorf("Unknown encryption protocol: %s", encryption_protocol)
return
}
return
}
func DecodePublicKey(raw string) (encryption_protocol string, pubkey []byte, err error) {
encryption_protocol, encoded_pubkey, found := strings.Cut(raw, ":")
if !found {
return "", nil, fmt.Errorf("Invalid encoded pubkey, no : in string")
}
pubkey, err = b85_decode(encoded_pubkey)
return
}
func Encrypt_cmd(cmd *utils.RemoteControlCmd, password string, other_pubkey []byte, encryption_protocol string) (encrypted_cmd utils.EncryptedRemoteControlCmd, err error) {
cmd.Password = password
cmd.Timestamp = time.Now().UnixNano()
plaintext, err := json.Marshal(cmd)
if err != nil {
return
}
iv, tag, ciphertext, pubkey, err := encrypt(plaintext, other_pubkey, encryption_protocol)
encrypted_cmd = utils.EncryptedRemoteControlCmd{
Version: cmd.Version, IV: b85_encode(iv), Tag: b85_encode(tag), Pubkey: b85_encode(pubkey), Encrypted: b85_encode(ciphertext)}
if encryption_protocol != "1" {
encrypted_cmd.EncProto = encryption_protocol
}
return
}
func Encrypt_data(data []byte, other_pubkey []byte, encryption_protocol string) (ans []byte, err error) {
d := make([]byte, 0, uint64(len(data))+32)
d = fmt.Appendf(d, "%s:", strconv.FormatInt(time.Now().UnixNano(), 10))
d = append(d, data...)
iv, tag, ciphertext, pubkey, err := encrypt(d, other_pubkey, encryption_protocol)
if err != nil {
return
}
ec := utils.EncryptedRemoteControlCmd{
IV: b85_encode(iv), Tag: b85_encode(tag), Pubkey: b85_encode(pubkey), Encrypted: b85_encode(ciphertext)}
if encryption_protocol != "1" {
ec.EncProto = encryption_protocol
}
ans, err = json.Marshal(ec)
return
}
// }}}
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