Making Crypto Libraries Robust Against Physical Side-channel Attacks

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Alam, Md Monjur
Prvulovic, Milos
Zajić, Alenka
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The connection between theoretical and applied cryptography is often not well established due to difficulties in translating the theoretical security proofs to real world software and hardware implementations. Physical side-channel cryptanalysis is a very effective approach to break a secure cryptographic system. Most side-channel attacks on cryptographic primitives and implementations rely on different control flow or memory access patterns. As a countermeasure, the cryptographic community has established the notion of constant time program code which avoids secret-dependent control flow and data access patterns. This thesis focuses on detailing a set of new techniques to exploit widely used open sources for software implementations of cryptographic primitives. First, we present One&Done, a side-channel attack that is based on the analysis of signals that correspond to the brief computation activity that computes the value of each window during exponentiation, i.e. activity between large-integer multiplications. As the attack is message-independent, it makes the attack completely immune to existing countermeasures that focus on thwarting chosen-ciphertext attacks and/or square/multiply sequence analysis. Second, we present Nonce@Once, the first side-channel attack that recovers the secret scalar from the electromagnetic signal that corresponds to a single signing operation in current versions of Libgcrypt, OpenSSL. Our attack uses the signal differences created by systematic differences in operand values during a conditional swap operation itself to recover each bit of the secret. We also propose a mitigation that randomizes the exclusive-or mask in the conditional swap operation, is effective in preventing this and similar attacks. Next, we present a physical side-channel attack on DSA implementation, which utilizes constant-time fixed-window (m-ary) modular exponentiation. We demonstrated different implementation aspects and their effects as countermeasures which embrace the importance of re-thinking before designing and implementing PKC, in general. Lastly, We present the security issues on NAF based OpenSSL's ECDSA implementation.
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