References

Hill, L.S., 1929. Cryptography in an algebraic alphabet. Am. Math. Monthly, 36: 306-312.
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Hill, L.S., 1931. Concerning certain linear transformation apparatus of cryptography. Am. Math. Mon., 38: 135-154.
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Ismail, I.A., M. Amin and H. Diab, 2006. How to repair the hill cipher. J. Zhejiang Univ. Sci., 7: 2022-2030.
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Magamba, K., S. Kadaleka and A. Kasambara, 2012. Variable-length hill cipher with MDS key matrix. Cornell University. http://arxiv.org/ftp/arxiv/papers/1210/1210.1940.pdf.

Rangel-Romero, Y., R. Vega-Garcia, A. Menchaca-Mendez, D. Acoltzi-Cervantes, L. Martinez-Ramos et al., 2008. Comments on how to repair the hill cipher. J. Zhejiang Univ. Sci., 9: 211-214.
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Sastry, V.U.K., A. Varanasi and S.U. Kumar, 2011. A modern advanced hill cipher involving a permuted key and modular arithmetic addition operation. J. Global Res. Comput. Sci., 2: 92-97.