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title Encrypting and Decrypting Strings in Visual Basic
ms.custom
ms.date 07/20/2015
ms.prod .net
ms.reviewer
ms.suite
ms.technology
devlang-visual-basic
ms.tgt_pltfrm
ms.topic article
helpviewer_keywords
encryption [Visual Basic], strings
strings [Visual Basic], encrypting
decryption [Visual Basic], strings
strings [Visual Basic], decrypting
ms.assetid 1f51e40a-2f88-43e2-a83e-28a0b5c0d6fd
caps.latest.revision 18
author dotnet-bot
ms.author dotnetcontent

Walkthrough: Encrypting and Decrypting Strings in Visual Basic

This walkthrough shows you how to use the xref:System.Security.Cryptography.DESCryptoServiceProvider class to encrypt and decrypt strings using the cryptographic service provider (CSP) version of the Triple Data Encryption Standard (xref:System.Security.Cryptography.TripleDES) algorithm. The first step is to create a simple wrapper class that encapsulates the 3DES algorithm and stores the encrypted data as a base-64 encoded string. Then, that wrapper is used to securely store private user data in a publicly accessible text file.

You can use encryption to protect user secrets (for example, passwords) and to make credentials unreadable by unauthorized users. This can protect an authorized user's identity from being stolen, which protects the user's assets and provides non-repudiation. Encryption can also protect a user's data from being accessed by unauthorized users.

For more information, see Cryptographic Services.

Important

The Rijndael (now referred to as Advanced Encryption Standard [AES]) and Triple Data Encryption Standard (3DES) algorithms provide greater security than DES because they are more computationally intensive. For more information, see xref:System.Security.Cryptography.DES and xref:System.Security.Cryptography.Rijndael.

To create the encryption wrapper

  1. Create the Simple3Des class to encapsulate the encryption and decryption methods.

    [!code-vbVbVbalrStrings#38]

  2. Add an import of the cryptography namespace to the start of the file that contains the Simple3Des class.

    [!code-vbVbVbalrStrings#77]

  3. In the Simple3Des class, add a private field to store the 3DES cryptographic service provider.

    [!code-vbVbVbalrStrings#39]

  4. Add a private method that creates a byte array of a specified length from the hash of the specified key.

    [!code-vbVbVbalrStrings#41]

  5. Add a constructor to initialize the 3DES cryptographic service provider.

    The key parameter controls the EncryptData and DecryptData methods.

    [!code-vbVbVbalrStrings#40]

  6. Add a public method that encrypts a string.

    [!code-vbVbVbalrStrings#42]

  7. Add a public method that decrypts a string.

    [!code-vbVbVbalrStrings#43]

    The wrapper class can now be used to protect user assets. In this example, it is used to securely store private user data in a publicly accessible text file.

To test the encryption wrapper

  1. In a separate class, add a method that uses the wrapper's EncryptData method to encrypt a string and write it to the user's My Documents folder.

    [!code-vbVbVbalrStrings#78]

  2. Add a method that reads the encrypted string from the user's My Documents folder and decrypts the string with the wrapper's DecryptData method.

    [!code-vbVbVbalrStrings#79]

  3. Add user interface code to call the TestEncoding and TestDecoding methods.

  4. Run the application.

    When you test the application, notice that it will not decrypt the data if you provide the wrong password.

See Also

xref:System.Security.Cryptography
xref:System.Security.Cryptography.DESCryptoServiceProvider
xref:System.Security.Cryptography.DES
xref:System.Security.Cryptography.TripleDES
xref:System.Security.Cryptography.Rijndael
Cryptographic Services