International Association for Cryptologic Research

International Association
for Cryptologic Research


Okan Seker


A White-Box Masking Scheme Resisting Computational and Algebraic Attacks 📺
White-box cryptography attempts to protect cryptographic secrets in pure software implementations. Due to their high utility, white-box cryptosystems (WBC) are deployed by the industry even though the security of these constructions is not well defined. A major breakthrough in generic cryptanalysis of WBC was Differential Computation Analysis (DCA), which requires minimal knowledge of the underlying white-box protection and also thwarts many obfuscation methods. To avert DCA, classic masking countermeasures originally intended to protect against highly related side-channel attacks have been proposed for use in WBC. However, due to the controlled environment of WBCs, new algebraic attacks against classic masking schemes have quickly been found. These algebraic DCA attacks break all classic masking countermeasures efficiently, as they are independent of the masking order.In this work, we propose a novel generic masking scheme that can resist both DCA and algebraic DCA attacks. The proposed scheme extends the seminal work by Ishai et al. which is probing secure and thus resists DCA, to also resist algebraic attacks. To prove the security of our scheme, we demonstrate the connection between two main security notions in white-box cryptography: probing security and prediction security. Resistance of our masking scheme to DCA is proven for an arbitrary order of protection, using the well-known strong non-interference notion by Barthe et al. Our masking scheme also resists algebraic attacks, which we show concretely for first and second-order algebraic protection. Moreover, we present an extensive performance analysis and quantify the overhead of our scheme, for a proof-of-concept protection of an AES implementation.
Side-Channel Protections for Picnic Signatures 📺
We study masking countermeasures for side-channel attacks against signature schemes constructed from the MPC-in-the-head paradigm, specifically when the MPC protocol uses preprocessing. This class of signature schemes includes Picnic, an alternate candidate in the third round of the NIST post-quantum standardization project. The only previously known approach to masking MPC-in-the-head signatures suffers from interoperability issues and increased signature sizes. Further, we present a new attack to demonstrate that known countermeasures are not sufficient when the MPC protocol uses a preprocessing phase, as in Picnic3.We overcome these challenges by showing how to mask the underlying zero-knowledge proof system due to Katz–Kolesnikov–Wang (CCS 2018) for any masking order, and by formally proving that our approach meets the standard security notions of non-interference for masking countermeasures. As a case study, we apply our masking technique to Picnic. We then implement different masked versions of Picnic signing providing first order protection for the ARM Cortex M4 platform, and quantify the overhead of these different masking approaches. We carefully analyze the side-channel risk of hashing operations, and give optimizations that reduce the CPU cost of protecting hashing in Picnic by a factor of five. The performance penalties of the masking countermeasures ranged from 1.8 to 5.5, depending on the degree of masking applied to hash function invocations.
Extending Glitch-Free Multiparty Protocols to Resist Fault Injection Attacks
Side channel analysis and fault attacks are two powerful methods to analyze and break cryptographic implementations. At CHES 2011, Roche and Prouff applied secure multiparty computation to prevent side-channel attacks. While multiparty computation is known to be fault-resistant as well, the particular scheme used for side-channel protection does not currently offer this feature. This work introduces a new secure multiparty circuit to prevent both fault injection attacks and sidechannel analysis. The new scheme extends the Roche and Prouff scheme to make faults detectable. Arithmetic operations have been redesigned to propagate fault information until a new secrecy-preserving fault detection can be performed. A new recombination operation ensures randomization of the output in the case of a fault, ensuring that nothing can be learned from the faulty output. The security of the new scheme is proved in the ISW probing model, using the reformulated t-SNI security notion. Besides the new scheme and its security proof, we also present an extensive performance analysis, including a proof-of-concept, software-based AES implementation featuring the masking technique to resist both fault and side-channel attacks at the same time. The performance analysis for different security levels are given for the ARM-M0+ MCU with its memory requirements. A comprehensive leakage analysis shows that a careful implementation of the scheme achieves the expected security level.