Initial Bytes Research Articles

Formula omitted]: Efficient keyword matching for network traffic classification

Network traffic classification is required for a range of network management activities like meeting the Quality of Service demands of applications and security monitoring. Deep Packet Inspection (DPI) based methods achieve better classification accuracy compared to other techniques. However, DPI is computationally demanding and requires searching patterns in the payload. Methods found in the literature suffer from performance issues as they perform multiple scans of payload. In this paper, we describe KeyClass, which is a DPI based traffic classifier and can classify network flows with single scan of payload using keyword based signatures. KeyClass achieves performance gains (speed of classification) with a combination of two things. It quickly identifies potential application(s) by scanning few initial bytes of payload and optimize the number of character comparisons while searching remaining keywords of potential application(s). In order to identify potential applications, it uses a finite state machine constructed with first keyword of every application using classic Aho–Corasick multi-pattern matching algorithm. KeyClass has an application specific signature which is generated with the remaining set of keywords of an application. By skipping portions of payload from inspection, coupled with an efficient string matching algorithm, it practically achieves sub-linear search complexity. We evaluate the classification and execution performance of KeyClass with experiments using two large datasets containing 173619 and 885405 network flows and report that it has a good average classification accuracy of ≈ 98%. In our evaluation, KeyClass is found to be 3.79 times faster than state of the art methods.

An approach of refining RC4 with performance analysis on new variants

Many years of research on the RC4 stream cipher proves it to be strong enough, but there are claims that its swap function is responsible for essential biases in the output. There are suggestions to discard some initial bytes from the key-stream, to get rid of this, before the actual encryption starts, though no optimum value has been defined. In this paper, by analysing different variants of RC4, the authors have attempted to find out whether this cipher becomes more secure by discarding initial bytes and, if so, what is its optimum limit. Also, multiple S-boxes generated by different logics and a unique key-mixing procedure have been implemented, which made k RC4 more robust.

Proving empirical key-correlations in RC4

In view of the recent attacks on practical network protocols like WEP, WPA and TLS, there has been a renewed interest in the non-random behavior of RC4, the stream cipher that constitutes the core of all these protocols. While most of the non-random events in the cipher, more commonly known as ‘biases’, are initially reported as experimental observations, it is equally important to present theoretical proofs of such biases to justify the attacks based on these. In this paper, we provide theoretical proofs of all significant empirical correlations between the initial bytes of the RC4 keystream and its secret key, as experimentally observed by Sepehrdad, Vaudenay and Vuagnoux in SAC 2010.

(Non-)Random Sequences from (Non-)Random Permutations—Analysis of RC4 Stream Cipher

RC4 has been the most popular stream cipher in the history of symmetric key cryptography. Its internal state contains a permutation over all possible bytes from 0 to 255, and it attempts to generate a pseudo-random sequence of bytes (called keystream) by extracting elements of this permutation. Over the last twenty years, numerous cryptanalytic results on RC4 stream cipher have been published, many of which are based on non-random (biased) events involving the secret key, the state variables, and the keystream of the cipher. Though biases based on the secret key are common in RC4 literature, none of the existing ones depends on the length of the secret key. In the first part of this paper, we investigate the effect of RC4 keylength on its keystream, and report significant biases involving the length of the secret key. In the process, we prove the two known empirical biases that were experimentally reported and used in recent attacks against WEP and WPA by Sepehrdad, Vaudenay and Vuagnoux in EUROCRYPT 2011. After our current work, there remains no bias in the literature of WEP and WPA attacks without a proof. In the second part of the paper, we present theoretical proofs of some significant initial-round empirical biases observed by Sepehrdad, Vaudenay and Vuagnoux in SAC 2010. In the third part, we present the derivation of the complete probability distribution of the first byte of RC4 keystream, a problem left open for a decade since the observation by Mironov in CRYPTO 2002. Further, the existence of positive biases towards zero for all the initial bytes 3 to 255 is proved and exploited towards a generalized broadcast attack on RC4. We also investigate for long-term non-randomness in the keystream, and prove a new long-term bias of RC4.