International Association for Cryptologic Research (IACR)
Abstract
In traditional symmetric cryptography, the adversary has
access only to the inputs and outputs of a cryptographic primitive. In the
white-box model the adversary is given full access to the implementation.
He can use both static and dynamic analysis as well as fault analysis in
order to break the cryptosystem, e.g. to extract the embedded secret
key. Implementations secure in such model have many applications in
industry. However, creating such implementations turns out to be a very
challenging if not an impossible task.
Recently, Bos et al. proposed a generic attack on white-box primitives
called differential computation analysis (DCA). This attack was applied
to many white-box implementations both from academia and industry.
The attack comes from the area of side-channel analysis and the most
common method protecting against such attacks is masking, which in
turn is a form of secret sharing. In this paper we present multiple generic
attacks against masked white-box implementations. We use the term
“masking” in a very broad sense. As a result, we deduce new constraints
that any secure white-box implementation must satisfy.
Based on the new constraints, we develop a general method for protecting
white-box implementations. We split the protection into two independent
components: value hiding and structure hiding. Value hiding must pro-
vide protection against passive DCA-style attacks that rely on analysis
of computation traces. Structure hiding must provide protection against
circuit analysis attacks. In this paper we focus on developing the value
hiding component. It includes protection against the DCA attack by Bos
et al. and protection against a new attack called algebraic attack.
We present a provably secure first-order protection against the new al-
gebraic attack. The protection is based on small gadgets implementing
secure masked XOR and AND operations. Furthermore, we give a proof
of compositional security allowing to freely combine secure gadgets. We
derive concrete security bounds for circuits built using our construction