Crucial Security Layer: If you have Two-Step Verification (2FA) enabled for your account, you will be prompted for an additional password after successfully entering the verification code.
You must enter this 2FA password correctly to proceed.
Successful Login and Session Establishment:
Once both the phone number verification code and (if applicable) the 2FA password are correct, your device is authenticated.
A secure session is established between your device telegram number database and Telegram's servers using Telegram's MTProto protocol (which involves a Diffie-Hellman key exchange to create a secure, shared authorization key).
Your chats, contacts, and settings are then synchronized from the Telegram cloud to your new device. This device is now listed in your "Active Sessions" (Settings > Devices).
MTProto Cryptography: All communication between your device and Telegram's servers (including login requests and code delivery) is encrypted using Telegram's custom MTProto protocol, which is designed for robust security.
Two-Step Verification (2FA): This is the strongest defense against unauthorized access. Even if someone obtains your phone number and manages to intercept SMS codes (e.g., via a SIM swap attack), they cannot access your account without your 2FA password.
In-App Code Prioritization: Sending codes within the app to active sessions is more secure than SMS, as it bypasses the vulnerabilities inherent in SMS networks.
Active Sessions Management: You can review and terminate any suspicious active sessions from within your Telegram settings, adding another layer of control.
Decoupling Identity (Usernames & Fragment): While the phone number is used for login, Telegram allows you to set a public username and hide your phone number from others, promoting pseudonymity. Furthermore, Fragment's +888 anonymous numbers offer a way to create an account completely decoupled from personal phone identity.
In essence, Telegram's phone number login system is a core part of its identity and security model. It aims for simplicity and ease of use while providing robust cryptographic protection and additional security layers (like 2FA) that users are strongly encouraged to utilize.Quick Guide to Telegram Phone Number Settings.