# Differential fault analysis of secret key cryptosystems

## Abstract

In September 1996 Boneh, Demillo, and Lipton from Bellcore announced a new type of cryptanalytic attack which exploits computational errors to find cryptographic keys. Their attack is based on algebraic properties of modular arithmetic, and thus it is applicable only to public key cryptosystems such as RSA, and not to secret key algorithms such as the Data Encryption Standard (DES).

In this paper, we describe a related attack, which we call *Differential Fault Analysis*, or *DFA*, and show that it is applicable to almost any secret key cryptosystem proposed so far in the open literature. Our DFA attack can use various fault models and various cryptanalytic techniques to recover the cryptographic secrets hidden in the tarn per-resistant device. In particular, we have demonstrated that under the same hardware fault model used by the Bellcore researchers, we can extract the full DES key from a sealed tamper-resistant DES encryptor by analyzing between 50 and 200 ciphertexts generated from unknown but related plaintexts.

In the second part of the paper we develop techniques to identify the keys of completely unknown ciphers (such as Skipjack) sealed in tamper-resistant devices, and to reconstruct the complete specification of DES-like unknown ciphers.

In the last part of the paper, we consider a different fault model, based on permanent hardware faults, and show that it can be used to break DES by analyzing a small number of ciphertexts generated from completely unknown and unrelated plaintexts.

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