1. Initial Setup (Authorization Key Generation):
When you first use Telegram on a device, a critical step happens behind the scenes: the creation of an authorization key.
Diffie-Hellman Key Exchange (DH): Your Telegram telegram number database client (app) and the Telegram server engage in a secure Diffie-Hellman key exchange. This is a cryptographic handshake that allows both the client and server to establish a shared, secret authorization key without ever transmitting the key itself over the network.
Proof of Work (Optional but enhances security): In some cases, to deter brute-force attacks during key exchange, Telegram might require the client to perform a small "proof of work." This involves solving a minor computational puzzle.
Long-Term Key: This authorization key (usually 2048-bit RSA) is a long-term key stored securely on your device. It forms the basis of all future encrypted communication between your client and the Telegram server for that specific session. It's tied to the device, not just the phone number.
Client Request: When you enter your phone number in the app, your Telegram client sends a request to the server using the auth.sendCode method via an encrypted connection established with the authorization key (if one exists for that device, or a temporary key for new devices).
Server Response (Code Delivery Type): The server analyzes the request and determines the most secure and reliable way to send the verification code. It communicates this back to the client via the auth.SentCodeType constructor. This can be:
auth.SentCodeTypeSms: The standard SMS to your phone number.