TEXTSECURE is an app that claims to provide secure instant messaging and has a large number of installations via Google’s Play Store. Since Facebook bought WhatsApp, instant messaging apps with security guarantees became more and more popular. In this paper, they have provided a detailed security analysis of TEXTSECURE. They described the protocol and then performed a security analysis of the individual steps of the protocol. This led to the discovery of several weaknesses, most notably an UKS attack. Best to their knowledge, this is the first formal verification of the security guarantees offered by the tool.
Read the full paper here - https://eprint.iacr.org/2014/904.pdf