Theory Agents

(*******************************************************************************

  Project: Development of Security Protocols by Refinement

  Module:  Refinement/Agents.thy (Isabelle/HOL 2016-1)
  ID:      $Id: Agents.thy 133854 2017-03-20 17:53:50Z csprenge $
  Author:  Christoph Sprenger, ETH Zurich <sprenger@inf.ethz.ch>

  Agents and nonces (partly based on Paulson's Message.thy)

  Copyright (c) 2009-2016 Christoph Sprenger 
  Licence: LGPL

*******************************************************************************)

section ‹Atomic messages›

theory Agents imports Main 
begin

text ‹The definitions below are moved here from the message theory, since
the higher levels of protocol abstraction do not know about cryptographic 
messages.›


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subsection ‹Agents›
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datatype  ― ‹We allow any number of agents plus an honest server.›
  agent = Server | Agent nat

consts 
  bad :: "agent set"			      ― ‹compromised agents›

specification (bad)
  Server_not_bad [iff]: "Server ∉ bad"
    by (rule exI [of _ "{Agent 0}"], simp)

abbreviation 
  good :: "agent set"
where
  "good ≡ -bad"

abbreviation 
  Sv :: "agent"
where
  "Sv ≡ Server"


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subsection ‹Nonces›
(******************************************************************************)

text ‹We have an unspecified type of freshness identifiers. 
For executability, we may need to assume that this type is infinite.›

typedecl fid_t

datatype fresh_t = 
  mk_fresh "fid_t" "nat"      (infixr "$" 65) 

fun fid :: "fresh_t ⇒ fid_t" where
  "fid (f $ n) = f"

fun num :: "fresh_t ⇒ nat" where
  "num (f $ n) = n"


text ‹Nonces›

type_synonym 
  nonce = "fresh_t"


end