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SymmetricAlgorithm.IV Property

Gets or sets the initialization vector (IV) for the symmetric algorithm.

Namespace:  System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)

public virtual byte[] IV { get; set; }

Property Value

Type: System.Byte[]
The initialization vector.


An attempt was made to set the initialization vector to null.


An attempt was made to set the initialization vector to an invalid size.

The IV property is automatically set to a new random value whenever you create a new instance of one of the SymmetricAlgorithm classes or when you manually call the GenerateIV method. The size of the IV property must be the same as the BlockSize property divided by 8.

The classes that derive from the SymmetricAlgorithm class use a chaining mode called cipher block chaining (CBC), which requires a key and an initialization vector to perform cryptographic transformations on data. To decrypt data that was encrypted using one of the SymmetricAlgorithm classes, you must set the Key property and IV property to the same values that were used for encryption.

For a given secret key k, a simple block cipher that does not use an initialization vector will encrypt the same input block of plain text into the same output block of cipher text. If you have duplicate blocks within your plain text stream, you will have duplicate blocks within your cipher text stream. If unauthorized users know anything about the structure of a block of your plain text, they can use that information to decipher the known cipher text block and possibly recover your key. To combat this problem, information from the previous block is mixed into the process of encrypting the next block. Thus, the output of two identical plain text blocks is different. Because this technique uses the previous block to encrypt the next block, an initialization vector is needed to encrypt the first block of data.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.