In recent weeks the concept of (perfect) forward security/secrecy has been mentioned a lot, primarily in the context of the shocking revelations about NSA eavesdropping. As far as I'm aware, this concept was introduced by C. G. Günther in . Unfortunately  only sketches the concept but does not give a security definition. The survey  gives a formal security definition only for forward secure pseudo-random generators. The textbooks [3, 4, 5, 6] all don't even mention the concept, and the relevant Wikipedia article is near unreadable.
Could somebody please point me towards a formal definition of (perfect) forward security/secrecy?
- C. G. Günther, "An Identity-based Key-exchange Protocol".
- G. Itkis, "Forward Security: Adaptive Cryptography: Time Evolution".
- J. Katz, Y. Lindell, "Introductin to Modern Cryptography".
- O. Goldreich, "Foundations of Cryptography".
- J. Hoffstein, J. Pipher, J. H. Silverma, "An Introduction to Mathematical Cryptography".
- D. R. Stinson, "Cryptography: Theory and Practise".