One of the things some people have asked me is what the difference between the HC modes and the forward secrecy provided by protocols such as SCIMP or  ZRTP. SCIMP has a one-way key derivation, similar to my Hash Chain Prefix  (HCP) mode. Since it is supposed that messages sent are short, I see no […]

In my previous post I presented some modes of operation of block ciphers to provide forward secrecy. Today I will let my imagination fly over Hollywood with this use case: Suppose Alice, a US secret agent working in China, has managed to break into a computer from a top-secret Chinese government agency and she has […]

Off-the-Record Messaging (OTR) is a protocol that allows people to chat in realtime securely and privately.  One of the most interesting features I’ve found in OTR is the ability to provide Perfect Forward Secrecy (PFS). Simply stated, an encryption system provides forward secrecy if even if suddenly all private keys in existence are compromised, an […]