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/crypto/cipher_encrypt.go

@@ -0,0 +1,55 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"io"
+
+	"github.com/gotd/ige"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+func countPadding(l int) int { return 16 + (16 - (l % 16)) }
+
+// encryptMessage encrypts plaintext using AES-IGE.
+func (c Cipher) encryptMessage(k AuthKey, plaintext *bin.Buffer) (EncryptedMessage, error) {
+	offset := len(plaintext.Buf)
+	plaintext.Buf = append(plaintext.Buf, make([]byte, countPadding(offset))...)
+	if _, err := io.ReadFull(c.rand, plaintext.Buf[offset:]); err != nil {
+		return EncryptedMessage{}, err
+	}
+
+	messageKey := MessageKey(k.Value, plaintext.Buf, c.encryptSide)
+	key, iv := Keys(k.Value, messageKey, c.encryptSide)
+	aesBlock, err := aes.NewCipher(key[:])
+	if err != nil {
+		return EncryptedMessage{}, err
+	}
+	msg := EncryptedMessage{
+		AuthKeyID:     k.ID,
+		MsgKey:        messageKey,
+		EncryptedData: make([]byte, len(plaintext.Buf)),
+	}
+	ige.EncryptBlocks(aesBlock, iv[:], msg.EncryptedData, plaintext.Buf)
+	return msg, nil
+}
+
+// Encrypt encrypts EncryptedMessageData using AES-IGE to given buffer.
+func (c Cipher) Encrypt(key AuthKey, data EncryptedMessageData, b *bin.Buffer) error {
+	b.Reset()
+	if err := data.EncodeWithoutCopy(b); err != nil {
+		return err
+	}
+
+	msg, err := c.encryptMessage(key, b)
+	if err != nil {
+		return err
+	}
+
+	b.Reset()
+	if err := msg.Encode(b); err != nil {
+		return err
+	}
+
+	return nil
+}