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    "How to construct more secure ciphers by the original cipher"

    In the situation where the security of a cipher decreases, the post-cipher with both higher security and compatibility to the original cipher is required until a totally new cipher will have spread. In this paper we propose an idea to construct a more secure cipher with compatibility to the original block cipher. The known schemes such as triple-DES do not provide the security corresponding to the key size. Our scheme provides the security corresponding to both the key size and the number of original-cipher repetitions under a certain condition. Furthermore we show that breaking our scheme is at least as hard as breaking the original block cipher.

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