Ciphers are standard and fast. Key handling is where a private messaging design is won or lost.
Encryption algorithms are rarely the weak point in a private messaging system. They are the part that has been studied, attacked and standardised for decades. The weak point is almost always the key.
A 2018 study on protecting chat content shows this by where it spends its design effort. AES handles the message itself. Almost everything else in the proposal is about making sure the right person, and only the right person, can unlock it.
The proposed system generates a key from sixteen random numbers, then disguises that key with several layers of MD5 hashing tied to private values that live inside the application. Sending a message means sending both the encrypted content and enough information for the recipient to rebuild the key.
That structure raises questions every messaging product has to answer.
The performance results are reassuring on this front. On a low spec Android handset, encryption and decryption stayed between a few milliseconds and a few tens of milliseconds for messages up to a thousand characters, well inside what users perceive as instant.
That is the useful takeaway for teams building private communication features. Fast cryptography is available off the shelf. The work that decides whether a feature is genuinely private happens in the design of the key, its storage, and the recovery path.
Wardhono et al. (2018). End-to-End Privacy Protection for Facebook Mobile Chat based on AES with Multi-Layered MD5. International Journal of Interactive Mobile Technologies.
