Hi all,

Abstract: In device independent quantum key distribution (DIQKD) Alice
and Bob try to establish a shared secret key without trusting the
devices used in key generation. The setup must therefore be treated as a
black box and is mathematically described by a conditional probability
distribution. Security proofs of DIQKD protocols can be simplified if
the attacker can be restricted to attack each round in the key
distribution process in an identical fashion (collective attacks). For
many protocols such a reduction is available through the entropy
accumulation theorem (EAT), but there are interesting protocols where
the EAT is not applicable. In this presentation we introduce two de
Finetti theorems that relate the properties of an arbitrary
Clauser-Horne-Shimony-Holt (CHSH) symmetric quantum black box to a
convex combination of iid quantum black boxes (de Finetti boxes). We
further discuss how these theorems could be used in DIQKD security
proofs, even if the EAT is not applicable, to impose restrictions on the
attacker.