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Cache-timing techniques: Exploiting the DSA algorithm
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Perustieteiden korkeakoulu |
Master's thesis
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SCI3071
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en
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70 + 8
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Abstract
Side-channel information is any type of information leaked through unexpected channels due to physical features of a system dealing with data. The memory cache can be used as a side-channel, leakage and exploitation of side-channel information from the executing processes is possible, leading to the recovery of secret information. Cache-based side-channel attacks represent a serious threat to implementations of several cryptographic primitives, especially in shared libraries. This work explains some of the cache-timing techniques commonly used to exploit vulnerable software. Using a particular combination of techniques and exploiting a vulnerability found in the implementation of the DSA signature scheme in the OpenSSL shared library, a cache-timing attack is performed against the DSA’s sliding window exponentiation algorithm. Moreover, the attack is expanded to show that it is possible to perform cache-timing attacks against protocols relying on the DSA signature scheme. SSH and TLS are attacked, leading to a key-recovery attack: 260 SSH-2 handshakes to extract a 1024/160-bit DSA hostkey from an OpenSSH server, and 580 TLS 1.2 handshakes to extract a 2048/256-bit DSA key from an stunnel server.