Debreach: Mitigating Compression Side Channels via Static Analysis and Transformation Compression is an emerging source of exploitable sidechannel leakage that threatens data security, particularly in web applications where compression is indispensable for performance reasons. Current approaches to mitigating compression side channels have drawbacks in that they either degrade compression ratio drastically or require too much effort from developers to be widely adopted. To bridge the gap, we develop Debreach, a static analysis and program transformation based approach to mitigating compression side channels. Debreach consists of two steps. First, it uses taint analysis to soundly identify flows of sensitive data in the program and uses code instrumentation to annotate data before feeding them to the compressor. Second, it enhances the compressor to exploit the freedom to not compress of standard compression protocols, thus removing the dependency between sensitive data and the size of the compressoru0027s output. Since Debreach automatically instruments applications and does not change the compression protocols, it has the advantage of being nondisruptive and compatible with existing systems. We have evaluated Debreach on a set of web server applications written in PHP. Our experiments show that, while ensuring leakagefreedom, Debreach can achieve significantly higher compression performance than stateoftheart approaches.

Mitigating Both Data Corruption and Content Replay Attacks with Implicit Data Integrity We study the security of the recently proposed implicit integrity methodology. Implicit integrity is a novel methodology that supports corruption detection without producing, storing or verifying mathematical summaries of the content such as MACs or ICVs, as typically done today. The main idea behind implicit integrity is that, whereas typical user data demonstrate patterns such as repeated bytes or words, decrypted data resulting from corrupted ciphertexts no longer demonstrate such patterns. Thus, by checking the entropy of decrypted ciphertexts, corruption can be possibly detected. Past contributions to the implicit integrity methodology have focused on observed patterns on client and server data that motivate the methodology, entropy definitions for arbitrarily small messages, and constructions that mitigate data corruption attacks. In this paper, we extend the known analytical results concerning implicit integrity addressing content replay attacks as well. We demonstrate that the class of cryptographic constructions known as xe2x80x98random oracles according to observer functionsxe2x80x99, which has been proposed for mitigating data corruption attacks, is actually simultaneously secure under two different adversary models: an input perturbing adversary performing content corruption attacks, and an oracle replacing adversary performing content replay attacks.