can you help on this

[ragun...@gmail.com]

Greetings frnds

i am working on the folllowing area "Working over an Encoded data"

Homomorphic" is an adjective which describes a property of an encryption scheme. That property, in simple terms, is the ability to perform computations on the ciphertext without decrypting it first. Because this tends to sound either baffling or miraculous the first time you hear it, let's begin with a very simple example.

The popular but wildly insecure cipher scheme rot-13 (a.k.a. "Caesar cipher") is partially homomorphic, specifically with respect to the concatenation operation. Imagine we write an Encrypt and Decrypt function using the rot-13 algorithm. The "secret key" will be 13, the number of characters each letter is shifted. Let's encrypt two words and then concatenate the ciphertext, and finally decrypt the result. In psuedocode, this is:



LOGIC is this

var c1 = Encrypt(13, "HELLO"); // c1 = URYYB
var c2 = Encrypt(13, "WORLD"); // c2 = JBEYQ
var c3 = Concat (c1, c2); // c3 = URYYBJBEYQ
var p = Decrypt(13, c3); // p = HELLOWORLD







Instead of Giving Text i want to use files for Encoding and Decoding and some other algorithm.. can you help on this




Because it was not necessary to first decrypt the two fragments of ciphertext before performing the concatenation operation, we can say that rot-13 is homomorphic with respect to concatenation. In other words, it is possible to take two pieces of ciphertext and perform an operation on them which results in the ciphertext of the concatenation of the two respective pieces of plaintext.

Visually, it looks like this:

Homomorphic concat with Rot-13

It just so happens that in this case the homomorphic concatenation (concatenating the two fragments of ciphertext) is the same operation as the non-homomorphic concatenation (concatenating two fragments of plaintext). This is not always the case. What is important is that we can perform some operation on the input ciphertext which will produce new ciphertext that, when decrypted, will produce output plaintext corresponding to a desired operation on the input plaintext.

https://github.com/angelausy/cs111b/blob/master/fileIO/Append.java

http://www.cs.ucf.edu/~czou/research/EcryptedCloud-Globecom12.pdf


http://www.dreamincode.net/forums/topic/196577-help-with-vigener-cipher-project/