Lossless Text Compression

The basic requirement of Text compression mechanism is that the combination of compression & decompression mechanisms to be lossless otherwise data cannot be restored in actual format. The data compression by text substitution mechanism is used by [3][6]. The scheme of data compression mechanisms includes changes among various factors, like degree of compression, amount of distortion introduced; for lossy compression algorithm and the computational resources required to compress and uncompress data.

The mechanism given below is used for lossless text compression in the Color-Coded encryption at the source end employed by Huffman:

Huffman Encoding Compression Algorithm

The Huffman encoding algorithm is an optimal compression algorithm in which the occurrence of each letter or symbol is used to compress the data. The plan behind the technique is that if you are having some letters that are more repeated as compared to others and it makes logic to use lesser bits to encode those letters than to encode the less repeated letters [4]. This algorithm builds the bottom up tree using the occurrence of each letter or symbol.

First, every letter starts off as part of its own tree and trees are ordered by the occurrence of the letters in the actual string. Then the two least repeatedly used letters are combined into a single tree and the frequency of that tree is set to be the combined frequency of the two trees that it links together. This new tree is reinserted into the record of trees in its sorted place. The procedure is afterward repeated treating trees with more than one component the same as any other trees except that their frequencies are the sum of the frequencies of all of the letters at the leaves. This is just the sum of the left and right children of any node because each node stores the frequency information about its own children. The procedure completes when all of the trees have been combined into a single tree. This tree describes a Huffman compression encoding.

Normally tree is design from the bottom up manner: we start out with 256 trees and end up with a single tree with 256 leaves along with 255 internal nodes. The tree has attention-grabbing property: the occurrences of all of the internal nodes combined jointly will give the total number of bits required to write the encoded file

I. Proposed system

This paper proposes a cryptographic encryption and decryption method called Color coded cryptography which uses the color and Huffman compression techniques to compress the data. This is a symmetrical system which is implemented by encryption of text by converting it into colored image. Each character of the message is encrypted into some blocks of color. The inverse process is used to produce the original text from colored image at the receiver side.

Advantages of proposed System

Each character in the plaintext is substituted with a color blocks from the available 18 decillions of colors in the world and at the receiving end the cipher text block which is in colored image is decrypted into plain text. It is resilient against problems like Meet in the middle attack, Birthday attack and Brute force attacks [2]. The size of the plain text can be reduced when it is encrypted, in a lossless manner. The space occupied by the cipher text in the buffer is very less; hence transfer of cipher text through a transmission channel is very fast which subsequently brings down the transportation cost [2].

II. SYSTEM DSIGN AND WORKING

The problem definition is to suggest a system capable of carry out lossless data compression on binary data using encryption and decryption. It also works as a solution to the data protection needs of the user, holding important role in environments where privacy of data is critical and therefore contributing to information security. The encoding and compressing schemes need to be computationally and functionally efficient and must look up to provide an optimal solution to the above-mentioned problems.

The system is capable of taking input in the form of text files whose binary representation is processed and thereby encrypted in a color image. One of the suitable compression method for data compression which is known as Huffman encoding is used on the encrypted data to ensure a proper adjustment between the tasks performed and space complexity issues involved. The design should attain the best promising compression ratio, with the limited resources of a present-day computers. As a result, there are firm constraints on the memory usage and the compression speed of the design. The system presently aims to work with text file in standard ASCII based format.

The system performs on two aspects: On the Sender side this technique compresses the file using Huffman encoding and then encodes the binary file data into a color code encrypted JPEG image file. While On the Receiver side, it does the reverse i.e. decrypts the image and then decompresses it, bringing back the binary text file.