## Section: Scientific Foundations

### Logic as a tool for assessing computer security

The various efforts of the SECSI team are united by the reliance on
*logic* and rigorous methods. As already said in
Section
3.1 , SECSI does not do
any cryptology per se.

As far as cryptographic protocol verification is concerned, one
popular kind of model is that of Dolev and Yao (after
[82] , see [68] for a
survey), where: the intruder can read and write on every
communication channel, and in effect has full control over the
network; the intruder may encrypt, decrypt, build and destruct
pairs, as many times as it wishes; and, finally, cryptographic means
are assumed to be *perfect* . The latter in particular means
that the only way to compute the plaintext M from the ciphertext
{M}_{K} is to decrypt the latter using the inverse key K^{-1} .
It also means that no ciphertext can be confused with any message
that is not a ciphertext, and that {M}_{K} = {M^{'}}_{K'} implies
M = M^{'} and K = K^{'} . Thus, messages can be simply encoded as
first-order terms, a fact which has been used by many authors. This
“perfect cryptgraphy” model has been extended to algebraic
properties of primitives (see [75] for a survey)
which was one of the main themes of the RNTL project PROUVÉ.

As soon as cryptography has been abstracted using a term algebra, first-order logic is relevant to security proofs: security proofs can be tackled from the automata-theoretic point of view or using automated deduction. In SECSI we contributed (and continue to contribute) to this line of research designing strategies and decision methods, e.g. [86] , [69] .

The thrust here is on *more automation* .