Bounds on Key Appearance Equivocation for Substitution Ciphers
<|reference_start|>Bounds on Key Appearance Equivocation for Substitution Ciphers: The average conditional entropy of the key given the message and its corresponding cryptogram, H(K|M,C), which is reffer as a key appearance equivocation, was proposed as a theoretical measure of the strength of the cipher system under a known-plaintext attack by Dunham in 1980. In the same work (among other things), lower and upper bounds for H(S}_{M}|M^L,C^L) are found and its asymptotic behaviour as a function of cryptogram length L is described for simple substitution ciphers i.e. when the key space S_{M} is the symmetric group acting on a discrete alphabet M. In the present paper we consider the same problem when the key space is an arbitrary subgroup K of S_{M} and generalize Dunham's result.<|reference_end|>
@article{borissov2006bounds,
    title={Bounds on Key Appearance Equivocation for Substitution Ciphers},
    author={Yuri Borissov and Moon Ho Lee},
    journal={arXiv preprint arXiv:cs/0612064},
    year={2006},
    archivePrefix={arXiv},
    eprint={cs/0612064},
    primaryClass={cs.IT cs.CR math.IT}
}