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Breaking DVB-CSA

2012; Springer Science+Business Media; Linguagem: Inglês

10.1007/978-3-642-34159-5_4

1611-3349

Erik Tews, Julian Wälde, Michael P. Weiner,

Coding theory and cryptography

Digital Video Broadcasting (DVB) is a set of standards for digital television. DVB supports the encryption of a transmission using the Common Scrambling Algorithm (DVB-CSA). This is commonly used for PayTV or for other conditional access scenarios. While DVB-CSA support 64 bit keys, many stations use only 48 bits of entropy for the key and 16 bits are used as a checksum. In this paper, we outline a time-memory-tradeoff attack against DVB-CSA, using 48 bit keys. The attack can be used to decrypt major parts a DVB-CSA encrypted transmission online with a few seconds delay at very moderate costs. We first propose a method to identify plaintexts in an encrypted transmission and then use a precomputed rainbow table to recover the corresponding keys. The attack can be executed on a standard PC, and the precomputations can be accelerated using GPUs. We also propose countermeasures that prevent the attack and can be deployed without having to alter the receiver hardware.