qr code generator asp net c# User and Data Security in Visual C#

Paint QR Code ISO/IEC18004 in Visual C# User and Data Security

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The need to establish a shared secret key rules out relying solely on symmetric encryption for encrypting spontaneous network communications. For example, symmetric key encryption is not initially used between a Web client and Web server because users on the Internet aren t typically willing to wait several days while the Web site physically mails them a secret key. Instead, Web sessions are initially established by using asymmetric keys.

Most of the .NET Framework s cryptography functionality is built into the System.Security.Cryptography namespace, including the four implementations of symmetric encryption algorithms. Table 12-2 shows symmetric encryption algorithm classes.

Description The .NET Framework implementation of the Rijndael symmetric encryption algorithm. As a government encryption standard, this algorithm is also known as Advanced Encryption Standard, or AES. RijndaelManaged is the only .NET Framework symmetric encryption class that is fully managed. All other encryption classes call unmanaged code. Because of this, RijndaelManaged is the preferred choice when your application will be running in a partially trusted environment. An encryption standard designed to replace DES that uses variable key sizes. The Data Encryption Standard (DES) is a symmetric encryption algorithm that uses relatively short key lengths that are vulnerable to cracking attacks. As a result, it should be avoided. However, it remains commonly used because it is compatible with a wide range of legacy platforms.

Description The .NET Framework implementation of the Triple DES (3DES) symmetric encryption algorithm, it essentially applies the DES algorithm three times.

All symmetric algorithm classes are derived from the System.Security.Cryptography.SymmetricAlgorithm base class and share the following properties:

block size is the number of bits that the algorithm processes at a single time and can usually be ignored when creating applications that use encryption.

bits. The feedback size determines one aspect of the algorithm s encryption technique; however, as a developer, you can safely ignore this property.

Key property, both the encryptor and decryptor must specify the same value. To avoid the overhead of transferring the IV securely between the encryptor and decryptor, you might choose to statically define the IV in your application, or to derive this from the Key property.

NOTE Understanding initialization vectors (IVs)

An initialization vector (IV) is data that symmetric encryption algorithms use to further obscure the first block of data being encrypted, which makes unauthorized decrypting more difficult. You don t need to understand what IVs do to use encryption, as long as you know that you must synchronize the IV values for both the encryptor and decryptor.

Key Gets or sets the secret key for the symmetric algorithm. Keys are automat-

ically generated if you have not specifically defined them. After encryption, you must store this value and transfer it to the decryptor. During decryption, you must specify the same key used during encryption.

in bits. When you create a symmetric algorithm object, the runtime will choose the largest key size supported by the platform. As a result, you can usually ignore this property. However, if the message s recipient does not support the same key sizes as the sender, you must set this property to the highest value supported by both the encryptor and the decryptor.

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the symmetric algorithm. Each array member contains MinSize and MaxSize properties, which define the valid key ranges in bits; and a SkipSize property that specifies in bits the interval between valid key sizes.

symmetric algorithm. Each array member contains MinSize and MaxSize properties that define the valid key ranges in bits, and a SkipSize property that specifies the interval between valid key sizes in bits.

Mode A property set to one of the CipherMode enumeration values that deter-

mines one aspect of the encryption algorithm s behavior. This property is usually set to Cipher Block Chaining (CBC), the default. You should usually leave this set to CBC. If you do change this value, you must change it at both the encryptor and decryptor.