  This paper describes a novel bit level stream cipher based symmetric key
cryptographic technique. At first, sender and receiver agree upon a symmetric
key. Then the symmetric key is formed using Greatest Common Divisor (G.C.D) of
sum of even or odd bit positional weightth even or odd number and a symmetric
key value is derived from the symmetric by the sender. The symmetric key value
is XORed with the ASCII value of the plain text character to get the cipher
text character. This is repeated for the entire plain text file. The symmetric
key and the entire cipher text file is sent by the sender to the receiver. From
the symmetric key, the receiver calculates the symmetric key value. The
symmetric key value is XORed with the cipher text character to get back the
plain text character. When this process is repeated for every cipher text
character, then entire plain text file is formed by the decryption process.
This technique has several advantages like formation of symmetric key
dynamically, more emphasis on symmetric key value rather than the symmetric
key, security and equal applicability for encryption and decryption of a large
number of files of almost any type or extension.
