  This paper proposes a new block cipher termed as "Modular Arithmetic based
Block Cipher with Varying Key-Spaces (MABCVK)" that uses private key-spaces of
varying lengths to encrypt data files. There is a simple but intelligent use of
theory of modular arithmetic in the scheme of the cipher. Based on observed
implementation of the proposed cipher on a set of real data files of several
types, all results are tabulated and analyzed.The schematic strength of the
cipher and the freedom of using a long key-space expectedly can make it
reasonably nonvulnerable against possible cryptanalytic attacks. As a part of
the future scope of the work, it is also intended to formulate and implement an
enhanced scheme that will use a carrier image to have a secure transmission of
the private key.
