The idea is to prevent attackers from drawing conclusions about previous or subsequent keys when one key is cracked on a communication channel, so that earlier and later messages continue to be protected.
This technique generates new key pairs for every chat to create what is known as Perfect-Forward-Secrecy (PFS). The software uses Off-the-Record (OTR) messaging to encrypt users' messages. The expert was especially angered about the bug fix description, saying that the developers made an attempt to cover up their mistake claiming the fix became necessary because of backwards compatibility problems.Ĭryptocat is designed to provide a securely encrypted online chat facility. This meant the private Elliptic Curve Cryptography (ECC) keys would be "ridiculously small" and would present an ideal attack vector for brute force attacks. A function that expected an array of 15-bit integer values was actually handed a string of the digits 0 to 9 with the ASCII value of the digit taking the place of the 15-bit integer value and shrinking the possible values from 2^15 to 10. Thomas says that the vulnerability was triggered by a flaw in the code for converting strings into arrays of integers. On his web site, Steve Thomas has a massive go at the software developers. The security hole affects all versions of the chat software since 2.0, as the hole was only discovered and closed in version 2.0.42. According to security expert Steve Thomas, messages sent via Cryptocat between 17 October 2011 and 15 June 2013 are compromised.
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