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Phases are an exciting new feature that allows Verifpal to reliably model post-compromise security properties such as forward secrecy or future secrecy. When modeling with an active attacker, a new phase can be declared thus: ``` principal Alice[...] principal Bob [...] Bob -> Alice: b1 phase principal Alice[...] Alice -> Bob: a2 ``` In the above example, the attacker won't be able to learn a2 until the execution of everything that occured in phase 0 (the initial phase of any model) is concluded. Furthermore, the attacker can only manipulate a2 within the confines of the phases in which it is communicated. That is to say, the attacker will have knowledge of b1 when doing analysis in phase 1, but won't be able to manipulate b1 in phase 1. The attacker won't have knowledge of a2 during phase 0, but will be able to manipulate b1 in phase 0. Values are learned at the earliest phase in which they are communicated, and can only be manipulated within phases in which they are communicated, which can be more than one phase since Alice can for example send a2 later to Carol, to Damian... Importantly, values derived from mutations of b1 in phase 0 cannot be used to construct new values in phase 1. A pertinent example of how phases can be used has been added to the signal.vp and signal_small.vp models, where phases are used to model forward secrecy in the Signal Protocol for exchanges involving three messages and one message respectively. Phases support was already added to the Visual Studio Code and Vim extensions in a previous commit (ad26547f) and those extensions will be pushed onto their respective marketplaces shortly. The Verifpal User Manual will also be updated.
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