The Truth on TPy

In this note we refer to the security of the Py and TPy families, as discussed in several papers in recent years. We investigate the published attacks, and show that no attacks on TPy, TPypy and TPy6 have ever been published, whose complexities are within the bounds set by the security claims of these ciphers. Also, only a single attack on Py was published which may be considered within the scope of the security claims — as a response to this attack the Py family was tweaked to TPy, TPypy and TPy6. We conclude that the TPy family of ciphers is highly secure, and recommend using them in applications that require secure stream ciphers.