In C Programming

In this assignment you'll write a program that encrypts the alphabetic letters in a file using the Vigenre cipher. Your program will take two command line parameters containing the names of the file storing the encryption key and the file to be encrypted. The program must generate output to the console (terminal) screen as specified below.

Command Line Parameters 1. Your program must compile and run from the command line. 2. Input the required file names as command line parameters. Your program may NOT prompt the user to enter the file names. The first parameter must be the name of the encryption key file, as described below. The second parameter must be the name of the file to be encrypted, as also described below. The sample run command near the end of this document contains an example of how the parameters will be entered. 3. Your program should open the two files, echo the processed input to the screen, make the necessary calculations, and then output the ciphertext to the console (terminal) screen in the format described below. Note: If the plaintext file to be encrypted doesn't have the proper number (512) of alphabetic characters, pad the last block as necessary with the letter 'X'. Make sure that all the input characters are lower case only.

Encryption Key File Format The encryption key is plain text that may contain upper and lower case letters, numbers, and other text. The input must be stripped of all non-alphabetic characters. Please note that the input text must be converted to contiguous lower case letters to simplify the encryption process.

Format of the File to be Encrypted The file to be encrypted can be any valid text file with no more than 512 letters in it. (Thus, it's safe to store all characters in the file in a character array of size 512, including any padding characters.) Please note that the input text file will also generally have punctuation, numbers, special characters, and whitespace in it, which should be ignored. You should also ignore whether a letter is uppercase or lowercase in the input file. Thus, you should treat A and a the same in your program. In order to simply the encryption, all letters should be converted to lower case letters. In the event the plaintext input file is less than 512 characters, pad the input file with a lowercase x until the 512 character input buffer is full.

Output Format The program must output the following to the console (terminal) screen: 1. Echo the unmodified input key file 2. Echo the unmodified input plaintext file 3. Ciphertext output produced from running the cipher against the input plaintext file. The ciphertext output portion should consist of only lowercase letters in rows of exactly 80 letters per row, except for the last row, which may possibly have fewer. These characters should correspond to the ciphertext produced by encrypting all the letters in the input file. Please note that only the alphabetic letters in the input plaintext file will be encrypted. All other characters should be ignored.

Program Notes and Hints Your program must read in an input plaintext file that may contain uppercase letters, lowercase letters and non-letter characters. Your program must distinguish between these three groups so that only the letters get encrypted. All non-letter characters in the file are simply skipped and not counted as part of the plaintext. Please note that although both upper case and lower case letters will be encrypted, your program should convert an upper case input letter to the corresponding lower case letter, i.e., it should convert an A to an a. One possible breakdown to solve this problem is as follows:

1) Write a section of code or function that reads only the upper and lower case letters in the input file into an char array of size 512, storing only the appropriate lowercase letters in the character array. 2) Write a section of code or function that takes as input the array from section 1 and the encryption key and produces an array of ciphertext storing only lowercase letters. 3) Write a section of code or function that takes as input the array storing the ciphertext and outputs it to the screen in the format specified. Additional functions or code will be needed to echo the input key and plaintext files.

Sample Key File I think and think for months and years. Ninety-nine times, the conclusion is false. The hundredth time I am right. Albert Einstein Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. Albert Einstein

Sample Plaintext File Fall in love with some activity, and do it! Nobody ever figures out what life is all about, and it doesn't matter. Explore the world. Nearly everything is really interesting if you go into it deeply enough. Work as hard and as much as you want to on the things you like to do the best. Don't think about what you want to be, but what you want to do. Keep up some kind of a minimum with other things so that society doesn't stop you from doing anything at all. - Richard Feynman

Corresponding Encrypted Output File ntstvxlbyxdqgrxcdqopmpnigbyrdugvbasumqgrzxzrmynyiuchvhbsbzvnwnsldptisbnnqumwwvxa zxuafkmxlqpwpvvmlmjgkplammrrgrvxzmgpazuzwzqpzcriamxyefdvbctjbuylczxgceehhkttqpva czlzkyorwhszpatlnsfcqueezfuyefmassampvxdwervqhcxcvemwquiyshvwlvuvobuoosruvnhacoe shcknneussxfcgoaeblwndiadtbghrmrzzdjaardpfdbiyqieazczabruwglxzflagnwucgjlnkwqvml ddzwwgawaicbfyikvflamvgmegzobnrbxrepzvuaezqnqytunnqflkfpjlobfjmloqxkqqexkhkltiba dbclohkltibadbfpifjfqbatebobxpfjxdfkxqflkbjyoxzbpqebbkqfobtloiapqfjrixqfkdmoldob ppdfsfkdyfoqeqlbslirqflkxiyboqbf

Sample Run Command C or C++ program: prompt> ./a.out key1.txt plainText1.txt Java program: prompt> java vigenere key1.txt plainText1.txt