The Caesar cipher is one of the earliest known and simplest ciphers. It is a type of substitution cipher in

which each letter in the plaintext is 'shifted' a certain number of places down the alphabet. For example,

with a shift of 1, A would be replaced by B, B would become C, and so on. The method is named after

Julius Caesar, who apparently used it to communicate with his generals.

To pass an encrypted message from one person to another, it is first necessary that both parties have

the 'key' for the cipher, so that the sender may encrypt it and the receiver may decrypt it. For the Caesar

cipher, the key is the number of characters to shift the cipher alphabet.

Here is a quick example of the encryption and decryption steps involved with the Caesar cipher. The text

we will encrypt is 'defend the east wall of the castle, by sending 50 more soldiers there', with a shift

(key) of 1.

plaintext: defend the east wall of the castle, by sending 50 more soldiers there

ciphertext: FGHGPF VJG GCUV YCNN QH VJG ECUVNG, DA UGPFKPI 61 OQTG UQNFKGTU VJGTG

Write a C# program that allows the user to enter the following information into text boxes:

Whether they want to encrypt a message or decrypt a message

The key value (1 20)

The filename where the original message is located

The program should then either encrypt or decrypt the message, displaying the result in a list box. Test

your program by decrypting the text file secretMessage.txt. The key for this file is 1. You are required to create an array that will

be the cipher code. Any characters that are not part of the 26 letters of the alphabet and the 10 digits

should be passed through without changing them. When you create your cipher, add the digits 0-9 to

the end of the alphabet and shift for 36 total characters.

Then Add punctuation (. , ? ! ;) and a space as part of the characters of the available alphabet and part of the

cipher. So the above message would cipher to:

FGHGPFBVJGBGCUVBYCNNBQHBVJGBECUVNG!BD0BUGPFKPIB72BOQTGBUQNFKGTUBVJGTG

secretMessage.txt:

EQNNGIGBKUBCBVKOGBWPNKMGBCP0BQVJGTBKPB0QWTBNKHG?B0QWBJCXGBICKPGFBKPFGRGPFGPEG! 0QWBCTGBKPBCBPGYBRNCEG!BCPFB0QWTBCFWNVBNKHGBKUBITCFWCNN0BUVCTKPIB0QWBKPBVJG HCEG?B0QWBJCXGBEJQKEGUBVQBOCMG!BCPFB0QWBMPQYBKV?BVJGTGBKUBPQBUGETGVBTGEKRG HQTBUWEEGGFKPIBKPBEQNNGIGABGXGT0QPGBFQGUBKVBFKHHGTGPVN0!BKPBCBUV0NGBCNNBVJGKT QYP?BOQUVBUVWFGPVUBKPBEQNNGIG!BYJQBUWEEGGFBJQYGXGT!BUJCTGBEGTVCKP EJCTCEVGTKUVKEU?

3?BCXQKFBRTQETCUVKPCVKPI?BEQNNGIGBCECFGOKEUBKPBVJGBHKTUVBVGTOBYKNNBDG RCTVKEWNCTN0BFKHHKEWNVBDGECWUGBKVBKUBOCVGTKCNBVJCVB0QWBJCXGBPGXGTBUGGPBDGHQTG? RNWU!B0QWBCTGBHCEKPIBOWEJBJKIJGTBGZRGEVCVKQPU!BGURGEKCNN0BVJCVB0QWBCTGBVJGBQPG TGURQPUKDNGBHQTB0QWTBOQVKXCVKQPBCPFBUWEEGUU?BWPNKMGBJKIJBUEJQQN!BEQNNGIG GZRGEVUB0QWBVQBDWKNFB0QWTBGFWECVKQPBHTQOBVJGBDQVVQOBWR!BTCVJGTBVJCP TGIWTIKVCVKPIBYJCVGXGTBHCEVUBCBVGCEJGTBHGGFUB0QW?BVJKUBOGCPUBOWEJBOQTGBYQTM VJCPB0QWBCTGBWUGFBVQ? IKXGB0QWTUGNHBKPEGPVKXGUBVQBUVWF0BKPBCFXCPEG?BFQP'VBECUJB0QWTBRC0EJGEMBWPVKN 0QW'TGBHKPKUJGFBYKVJBVJCVBVGTOBRCRGT?BEGNGDTCVGBYKVJBHTKGPFUBCHVGTB0QW'XGBVCMGP VJGBVGUV?BVTGCVB0QWTUGNHBVQBUQOGVJKPIB0QW'XGBDGGPBYCPVKPIBCHVGTB0QWBHKPKUJB0QWT UVWF0KPIBIQCNU? EJQQUGB0QWTBRTKQTKVKGU?BKVBKUBPQVBRQUUKDNGBVQBHKVBKPBCNNBVJGBUCOGBUQEKCN! CECFGOKE!BGORNQ0OGPV!BCPFBNQIKUVKECNBTGURQPUKDKNKVKGUBKPBEQNNGIGBVJCVB0QWBFKF KPBJKIJBUEJQQN?BDGBTGCNKUVKEBCDQWVBJQYBOWEJBVKOGBKUBTGSWKTGFBVQBOGGVB0QWT CECFGOKEBQDNKICVKQPUBCPFBJQYBOWEJB0QWBECPBFGXQVGBVQBUQEKCNBCEVKXKVKGU?

4?BIGVBRCUUKQPCVGBCDQWVBUQOGVJKPI?BVCMGBCBOQOGPVBVQBTGHNGEVBQPBYJCVB0QWBGPLQ0 FQKPIBCPFBUVWF0KPI!BCPFBYJCVB0QW'TGBIGPWKPGN0BKPVGTGUVGFBKP?BYJCVBCTGB0QWT IQCNU;BYJCVBCTGB0QWTBRNCPU;BEQNNGIGBKUBCPQVJGTBUVGRBQPBVJGBNCFFGTBVQBVJGBTGUV QHB0QWTBNKHG?BYJCVBFQB0QWBYCPVBVQBFQBCHVGTBEQNNGIG!BCPFBJQYBYKNNBEQNNGIG RTGRCTGB0QWBHQTBVJCVBPGZVBUVGR;

5?BYQTMBQPB0QWTBIGPGTCNBGFWECVKQP?BOQUVBEQNNGIGUBTGSWKTGBCBDTQCFBTCPIGBQH ENCUUGUBKPBVJGBDGIKPPKPI!BQHVGPBTGHGTTGFBVQBCUB"IGPGTCNBGFWECVKQP"BQT "FKUVTKDWVKQP"BTGSWKTGOGPVU?BGXGPBKHB0QW'XGBCNTGCF0BFGENCTGFB0QWTBOCLQTBCPF MPQYBYJCVB0QWBYCPVBVQBUVWF0!BVJGBFKUVTKDWVKQPBTGSWKTGOGPVUBDWKNFBETKVKECN UMKNNUBUWEJBCUBYTKVVGPBCPFBQTCNBEQOOWPKECVKQP!BETKVKECNBVJKPMKPIBCPFBRTQDNGO UQNXKPIBUMKNNU?BMGGRB0QWTBOKPFBQRGPBCPFBNQQMBHQTBYC0UBVQBCRRN0BVJGUGBUMKNNU YKVJKPB0QWTBOCLQT? CPQVJGTBTGCUQPBVQBVCMGBCFXCPVCIGBQHBVJKUBDTQCFBTCPIGBQHBENCUUGUBKPBEQNNGIG KUBVJCVB0QW'TGBNKMGN0BVQBEJCPIGBECTGGTUBQXGTB0QWTBNKHGVKOG!BCPFBGXGPBCBENCUU QTBVYQBECPBOCMGBCPBKORCEVBKPBMPQY-JQYBCPFBWPFGTUVCPFKPI?BCPGEFQVCNN0!B0QWBCTG NKMGN0BVQBDGBKPBCBFKHHGTGPVBHKGNFBCVBVJGBGPFBQHB0QWTBECTGGTBVJCPBVJGBQPGBKP YJKEJB0QWBUVCTVGF?