Windows Form Application – Symmetric Key Encryption

Topics:

Simple Encryption/Decryption, String Manipulation & Conversion, File I/O, Sequential Text File, ComboBox Control, OpenFileDialog() Control, ASCII Character Set, Asc(), Chr(), SubString(), Mod Operator

Develop a Visual Basic Windows Forms application that will ‘encrypt’ (character shift) the characters in a string based on a symmetric key (process known as symmetric-key cryptography). The application must also ‘decrypt’ the message based on the symmetric key used.

Sample Windows Form Controls

General Requirements

The clear-text message (that will be ‘encrypted’) is to be stored in a text-file.
The text-file is to be selected using an OpenFileDialog runtime control object
Text-file contents are to be displayed in a Textbox control located on the Windows form (you can also use this textbox to input clear-text characters)
Keys are contained in a ComboBox control object. Users can select a particular key resulting in alternate cipher-text output
Keys are to be a minimum of 4 digits. Each key digit is used for encoding where your program will move to the next digit for every character in the clear-text message.
Since there are a limited number of digits in a key, your program must ‘wrap-back’ to the first digit
The selected key must be stored in an array
Using the same key for encryption, decrypt the cipher-text message and display it in a textbox on the Windows Form
Since only printable characters are used (see table), if the ANSI code becomes larger than 126, you will need to wrap around to the ANSI code 32 (space)
Use exception handling where needed.
Add comments throughout your code
Example: Using a sample key of 58912, the output would be as follows:

Clear Character

N

J

I

T

V

B

N

e

T

ASCII Code

78

74

73

84

32

86

66

78

101

84

ASCII Code + Key Value

83

82

82

85

34

91

74

87

102

86

Shifted Character

S

R

R

U

“

[

J

W

f

V

Clear-Text: “NJIT VBNet”

Cipher-Text: “SRRU”[JWfV”

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