move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/session/tdesktop/local_key.go

@@ -0,0 +1,93 @@
+package tdesktop
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/sha1" // #nosec G505
+	"crypto/sha512"
+
+	"github.com/go-faster/errors"
+	"golang.org/x/crypto/pbkdf2"
+
+	"github.com/gotd/ige"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+)
+
+// See https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/details/storage_file_utilities.cpp#L322.
+func createLegacyLocalKey(passcode, salt []byte) (r crypto.Key) {
+	iters := localEncryptNoPwdIterCount
+	if len(passcode) > 0 {
+		iters = localEncryptIterCount
+	}
+
+	key := pbkdf2.Key(passcode, salt, iters, len(r), sha1.New)
+	copy(r[:], key)
+	return r
+}
+
+// See https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/details/storage_file_utilities.cpp#L300.
+func createLocalKey(passcode, salt []byte) (r crypto.Key) {
+	iters := 1
+	if len(passcode) > 0 {
+		iters = kStrongIterationsCount
+	}
+
+	h := sha512.New()
+	_, _ = h.Write(salt)
+	_, _ = h.Write(passcode)
+	_, _ = h.Write(salt)
+
+	key := pbkdf2.Key(h.Sum(nil), salt, iters, len(r), sha512.New)
+	copy(r[:], key)
+	return r
+}
+
+// See https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/details/storage_file_utilities.cpp#L584.
+func decryptLocal(encrypted []byte, localKey crypto.Key) ([]byte, error) {
+	if l := len(encrypted); l%aes.BlockSize != 0 {
+		return nil, errors.Errorf("invalid length %d, must be padded to 16", l)
+	}
+	// Get encryptedKey.
+	var msgKey bin.Int128
+	n := copy(msgKey[:], encrypted)
+	encrypted = encrypted[n:]
+
+	aesKey, aesIV := crypto.OldKeys(localKey, msgKey, crypto.Server)
+	cipher, err := aes.NewCipher(aesKey[:])
+	if err != nil {
+		return nil, errors.Wrap(err, "create cipher")
+	}
+
+	decrypted := make([]byte, len(encrypted))
+	ige.DecryptBlocks(cipher, aesIV[:], decrypted, encrypted)
+
+	if h := sha1.Sum(decrypted); !bytes.Equal(h[:16], msgKey[:]) /* #nosec G401 */ {
+		return nil, errors.New("msg_key mismatch")
+	}
+	return decrypted, nil
+}
+
+// encryptLocal code may panic
+func encryptLocal(decrypted []byte, localKey crypto.Key) ([]byte, error) {
+	if l := len(decrypted); l%aes.BlockSize != 0 {
+		return nil, errors.Errorf("invalid length %d, must be padded to 16", l)
+	}
+	// Compute encryptedKey.
+	var msgKey bin.Int128
+	h := sha1.Sum(decrypted) // #nosec G401
+	copy(msgKey[:], h[:])
+
+	aesKey, aesIV := crypto.OldKeys(localKey, msgKey, crypto.Server)
+	cipher, err := aes.NewCipher(aesKey[:])
+	if err != nil {
+		return nil, errors.Wrap(err, "create cipher")
+	}
+
+	encrypted := make([]byte, 16+len(decrypted))
+	copy(encrypted, msgKey[:])
+	ige.EncryptBlocks(cipher, aesIV[:], encrypted[16:], decrypted)
+
+	return encrypted, nil
+}