Linear Cryptanalysis Using Multiple Approximations

We present a technique which aids in the linear cryptanalysis of a block cipher and allows for a reduction in the amount of data required for a successful attack. We note the limits of this extension when applied to DES, but illustrate that it is generally applicable and might be exceptionally successful when applied to other block ciphers. This forces us to reconsider some of the initial attempts to quantify the resistance of block ciphers to linear cryptanalysis, and by taking account of this new technique we cover several issues which have not yet been considered.