Secret Key Encryption Demo

• Download source code - 61.1 KB

Introduction

Encryption is the process of transforming electronic data from a "plain text" state to an unreadable state by use of a cipher, also known as an algorithm.

Although formerly pretty complex, encryption can now be implemented very easily in any .NET application using the various encryption classes in the System.Security.Cryptography namespace.

I've put together an encryption demo program that demonstrates how to encrypt and decrypt documents using the following encryption methods:

• AES (Advanced Encryption Standard)
• DES (Data Encryption Standard)
• RC2 ("Ron's Code" or "Rivest Cipher")
• Rijndael
• Triple DES (Triple Data Encryption Standard)

This application uses persistent keys in combination with the respective algorithms to encrypt and decrypt data.

Using the Code

• Pass the selected file to the Encrypt and Decrypt methods below:

Dim path As String = "C:\temp\Encryption\Encrypt-decrypt.doc"
Dim encrytedPath As String = String.Empty

encrytedPath = Encrypt(path)
MessageBox.Show("The following file has been encrypted:" & _
                          vbCrLf & vbCrLf & encrytedPath)

path = Decrypt(encrytedPath)
MessageBox.Show("The following file has been decrypted:" & _
                          vbCrLf & vbCrLf & path)

• Declare the instance of the AES class that will be used to encrypt and decrypt:

'Create the a new instance of AES
Private mAes As System.Security.Cryptography.Aes = _
                         System.Security.Cryptography.Aes.Create()

• The code for the Encrypt method:

''' <summary>
''' This function Encryptes a document and returns the encrypted document path.
''' </summary>
''' <param name="path">The path of the file to encrypt.</param>
''' <returns>The path of the encrypted file.</returns>
''' <remarks></remarks>
Private Function Encrypt(ByVal path As String) As String

    Dim outputPath As String = String.Concat(path, ".enc")

    'Encryption example using AES

    'Get a persisted key and vector
    Dim key As Byte() = GetKey()
    Dim iv As Byte() = GetIV()

    'When a new instance of the AES class is created, a new random Key and Vector (IV)
    ' are created automatically. You can use these to encrypt and decrypt your files,
    ' however, they are only good until a new instance of this class is created. Once
    ' a new random Key and Vector (IV) are created,
    ' you won't be able to decrypt files, because
    ' the Key and Vector (IV) will have changed. The solution is use them 1 time to 
    ' create a random Key and Vector (IV) (which can be viewed in the Immediate window 
    ' by typing "?mAes.Key" or "?mAes.IV",
    ' and pressing Enter), and then somehow persist it 
    ' in your application (like in a class, or in a .DLL,
    ' or in an encrypted file or something), 
    ' which I've done as an example in the GeyKey() and GetIV() methods.

    'The auto-generated random key can be used
    'by uncommenting these lines, and the corresponding
    'lines in the Decrypt method below
    'key = mAes.Key
    'iv = mAes.IV

    'Create the Encryptor using the Key and Vector (IV)
    Dim encryptor As ICryptoTransform = mAes.CreateEncryptor(GetKey(), GetIV())

    'Open both the input file for reading, and
    ' the output file for writing.
    Dim reader As New FileStream(path, FileMode.Open, FileAccess.Read)
    Dim writer As New FileStream(outputPath, FileMode.Create, FileAccess.Write)

    'Create an Encrypted Stream using the "encryptor" we created above
    Dim encryptedStream As _
                New System.Security.Cryptography.CryptoStream(writer, _
                encryptor, CryptoStreamMode.Write)

    Dim bites(1023) As Byte 'Stores 1 KB
    Dim bitesRead As Int32 = 0 'Number of Bytes read
    Dim totalBites As Int64 = 0 'Total Number of Bytes read


    'Loop through the entire file reading 1 kb at a time
    Do Until totalBites >= reader.Length

        bitesRead = reader.Read(bites, 0, 1024)
        'Read the bytes from the input file.

        encryptedStream.Write(bites, 0, bitesRead)
        'Write the encrypted bytes to the output file.

        totalBites += bitesRead

    Loop

    'Close and release streams:
    encryptedStream.Close()
    encryptedStream.Dispose()

    reader.Close()
    reader.Dispose()

    writer.Close()
    writer.Dispose()

    'Return the output file
    Return outputPath

End Function

• The code for the Decrypt method:

''' <summary>
''' This function Encryptes a document and returns the encrypted document path.
''' </summary>
''' <param name="path">The path of the file to encrypt.</param>
''' <returns>The path of the encrypted file.</returns>
''' <remarks></remarks>
Private Function Decrypt(ByVal path As String) As String

    Dim decryptedPath As String = path.Replace(".enc", "")

    Dim key As Byte() = GetKey()
    Dim iv As Byte() = GetIV()

    'You can use this to generate a new Key and Vector (IV)
    'for use in your applications.
    ' *** Do not use the key that comes with this demo, 
    ' because everyone who uses this demo will have it. ***
    'key = mAes.GenerateKey()
    'iv = mAes.GenerateIV()

    'Create the Decryptor using the Key and Vector (IV)
    Dim decryptor As ICryptoTransform = mAes.CreateDecryptor(key, iv)

    'Open both the input file for reading, and
    ' the output file for writing.
    Dim reader As New FileStream(path, FileMode.Open, FileAccess.Read)
    Dim writer As New FileStream(decryptedPath, _
                      FileMode.Create, FileAccess.Write)

    'Create an Encrypted Stream using 
    'the "encryptor" we created above
    Dim decryptedStream As _
                    New System.Security.Cryptography.CryptoStream(writer, _
                    decryptor, CryptoStreamMode.Write)

    Dim bites(1023) As Byte 'Stores 1 KB
    Dim bitesRead As Int32 = 0 'Number of Bytes read
    Dim totalBites As Int64 = 0 'Total Number of Bytes read


    'Loop through the entire file reading 1 kb at a time
    Do Until totalBites >= reader.Length

       bitesRead = reader.Read(bites, 0, 1024)
       'Read the bytes from the input file.

       decryptedStream.Write(bites, 0, bitesRead)
       'Write the encrypted bytes to the output file.

       totalBites += bitesRead

    Loop


    'Close and release streams:
    decryptedStream.Close()
    decryptedStream.Dispose()

    reader.Close()
    reader.Dispose()

    writer.Close()
    writer.Dispose()

    Return decryptedPath

End Function

• Persisted Key and Vector (IV):

'*** Just a note - DO NOT USE THIS KEY FOR YOUR OWN ENCRYPTION
' Create a new key by using the GenerateKey() method
Private Function GetKey() As Byte()

    '32 length byte array
    Dim key(31) As Byte
    key(0) = 195
    key(1) = 201
    key(2) = 141
    key(3) = 238
    key(4) = 118
    key(5) = 179
    key(6) = 108
    key(7) = 7
    key(8) = 37
    key(9) = 109
    key(10) = 7
    key(11) = 48
    key(12) = 66
    key(13) = 141
    key(14) = 2
    key(15) = 65
    key(16) = 213
    key(17) = 136
    key(18) = 141
    key(19) = 210
    key(20) = 78
    key(21) = 234
    key(22) = 83
    key(23) = 34
    key(24) = 41
    key(25) = 238
    key(26) = 152
    key(27) = 88
    key(28) = 228
    key(29) = 72
    key(30) = 160
    key(31) = 174

    Return key

End Function

'*** Just a note - DO NOT USE THIS Vector (IV) FOR YOUR OWN ENCRYPTION
' Create a new Vector (IV) by using the GenerateIV() method
Private Function GetIV() As Byte()

    '16 length byte array
    Dim IV(15) As Byte
    IV(0) = 30
    IV(1) = 185
    IV(2) = 3
    IV(3) = 73
    IV(4) = 26
    IV(5) = 247
    IV(6) = 159
    IV(7) = 124
    IV(8) = 211
    IV(9) = 112
    IV(10) = 251
    IV(11) = 231
    IV(12) = 69
    IV(13) = 25
    IV(14) = 132
    IV(15) = 1

    Return IV

End Function

Points of Interest

The process for encrypting and decrypting each of the different algorithms is the same. One of the things you will find different is the number of bytes that are used in the different key and vector arrays.

Hopefully, this demo is helpful to you!