✳️ SECURITY | CRYPTOGRAPHY ✳️

📕 ABSTRACT 📕


▶️Telegram is a popular messaging app which supports end-to-end encrypted communication. In Spring 2015 we performed an audit of Telegram's source code. This short paper summarizes our findings.

▶️ Our main discovery is that the symmetric encryption scheme used in Telegram -- known as MTProto -- is not IND-CCA secure, since it is possible to turn any ciphertext into a different ciphertext that decrypts to the same message.

▶️ We stress that this is a theoretical attack on the definition of security and we do not see any way of turning the attack into a full plaintext-recovery attack. At the same time, we see no reason why one should use a less secure encryption scheme when more secure (and at least as efficient) solutions exist.

▶️ The take-home message (once again) is that well-studied, provably secure encryption schemes that achieve strong definitions of security (e.g., authenticated-encryption) are to be preferred to home-brewed encryption schemes.

#security #cryptography #cryptanalysis #MTProto