Forward secrecy

Forward secrecy is seen as an important security feature by several large Internet information providers. Since late 2011, Google has provided forward secrecy with TLS by default to users of its Gmail service, along with Google Docs and encrypted search among other services. Since November of 2013, Twitter has provided forward secrecy with TLS to users of its service. As of December 2013, 46.7% of TLS-enabled websites support some of cipher suites which provide forward secrecy.

 

Forward secrecy is obtained by generating new key material for each session, that is generating an ephemeral key to be used for all messages of a conversation (e.g. by using a Diffie–Hellman key exchange): in a worst-case scenario (such as arrest with live forensics performed on the device to retrieve the current ephemeral key in-memory), an adversary could only retroactively decode the ciphertext for the messages exchanged during that conversation, but none from the previous conversations.

 

Public-key systems which generate random public keys per session for the purposes of key agreement which are not based on any sort of deterministic algorithm demonstrate a property referred to as perfect forward secrecy. This means that the compromise of one message cannot lead to the compromise of others, and also that there is not a single secret value which can lead to the compromise of multiple messages.

 

http://en.wikipedia.org/wiki/Forward_secrecy

 

See also Twitter blog Forward Secrecy at Twitter.