Technical Terms and Abbreviations Glossary: M
Man-in-the-middle attack, Multi-Device Functionality
In cryptography and computer security, a man-in-the-middle, monster-in-the-middle, machine-in-the-middle, monkey-in-the-middle (MITM) or person-in-the-middle (PITM) attack is a cyberattack where the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other. One example of a MITM attack is active eavesdropping, in which the attacker makes independent connections with the victims and relays messages between them to make them believe they are talking directly to each other over a private connection, when in fact the entire conversation is controlled by the attacker. The attacker must be able to intercept all relevant messages passing between the two victims and inject new ones. This is straightforward in many circumstances; for example, an attacker within the reception range of an unencrypted Wi-Fi access point could insert themselves as a man-in-the-middle.
As it aims to circumvent mutual authentication, a MITM attack can succeed only when the attacker impersonates each endpoint sufficiently well to satisfy their expectations. Most cryptographic protocols include some form of endpoint authentication specifically to prevent MITM attacks. For example, TLS can authenticate one or both parties using a mutually trusted certificate authority.
Some instant messaging services (IMS for short) already offer «multi-device functionality» with only one user ID for all of your devices, usually called «ID». However, previous solutions are not really secure! Investigating authorities, secret services and criminals therefore have an easy time intercepting WA, FC, Telegram etc.
To do this, a device will be registered at the IMS for multi-device support in the name of the owner. The attacker tells the IMS the identification of the person to be intercepted, usually the mobile phone number. The IMS sends the owner a security query via SMS. However, the attacker intercepts this and the attack remains unnoticed. The solution of the IMS Threema is at a development stage where technical details are still subject to change, but the basic framework has been built.