C++ PROGRMMING LANGUAGE

PROJECT: Encryption and Decryption

Encryption is widely used on the internet to protect user information being sent between a browser and a server, including passwords, payment information and other personal information that should be considered private. An encryption algorithm is applied to the plain text to generate cipher text that cant be recognized easily. Decryption is simply the inverse of encryption.

We will practice the idea of encryption and decryption in this assignment based on string manipulation. Given a string plaintext, it is encrypted as following:

plaintext is first shifted right length() / 2 positions (toward higher index).

Next each letter is transformed:

If an uppercase letter: 'A'->'Z', 'B'->'Y', ... 'M'->'N', 'N'->'M', ..., 'Y'->'B', 'Z'->'A'

If a lowercase letter: same idea as for uppercase letter. i.e. 'a' -> 'z', 'b'->'y', ..., 'y'->'b', 'z'->'a'

If a digit: same idea as for uppercase letter. i.e. '0' ->'9', '1'->'8', '2'->'7' ...

Anything else remains the same.

For example, given a plain text of Secret 12, its changed into:

// index: 0 1 2 3 4 5 6 7 8

// S e r e c t 1 2

// length is 9, so shift 4 times toward right (9/2 is 4, int division. If length is 10, should shift 5 times)

// After shifting:

t 1 2 S e r e c

// next change each character:

g 8 7 H v x i v

Your program should include at least the following:

One function to encrypt a given plain text string as explained above. It should return a string containing the corresponding cipher text.

One function to decrypt a cipher text that has been encrypted as explained above. This function should return the decrypted text as a string.

You may add additional function(s) which is(are) necessary for your design.

Include in your main() one or more testing cases, with each testing case tests both the encryption function and the decryption function:

std::string str = "Secret 12";

std::string secretStr = encrypt(str);

std::cout

std::cout

std::cout

Your .cpp file should also contain:

Algorithms (pseudo code) for your encryption function as block comments at the beginning of your source code file. If you choose to draw flowchart, include it in your HW document instead.

/*IN*/, /*OUT*/, /*INOUT*/ comments to each function parameter.

Pre- and Post- condition comments for each function.

Do not use global variables (a 5% penalty).

Provide at least three testing cases (sample input and expected output for each testing case) and explain why you pick those three. Provide screenshots of the execution matching your three testing cases.

Comment your program appropriately. Pay attention to the standard stuff like coding style, indention, heading, and curly braces.

priginal Secret 12 encrypted: g 87Hvxiiu