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SymmetricKeyAlgorithmProvider.BlockLength | blockLength property

Gets the size, in bytes, of the cipher block for the open algorithm.


var blockLength = symmetricKeyAlgorithmProvider.blockLength;

Property value

Type: Number [JavaScript] | System.UInt32 [.NET] | uint32 [C++]

Block size.


If you are not using a PKCS#7 block padding algorithm (which automatically pads your content to the correct length), you must ensure that the message to be encrypted is an exact multiple of the length supported by the algorithm. For more information, see the following code example.


public IBuffer SampleCipherEncryption(
    String strMsg,
    String strAlgName,
    UInt32 keyLength,
    out BinaryStringEncoding encoding,
    out IBuffer iv,
    out CryptographicKey key)
    // Initialize the initialization vector.
    iv = null;

    // Initialize the binary encoding value.
    encoding = BinaryStringEncoding.Utf8;

    // Create a buffer that contains the encoded message to be encrypted. 
    IBuffer buffMsg = CryptographicBuffer.ConvertStringToBinary(strMsg, encoding);

    // Open a symmetric algorithm provider for the specified algorithm. 
    SymmetricKeyAlgorithmProvider objAlg = SymmetricKeyAlgorithmProvider.OpenAlgorithm(strAlgName);

    // Demonstrate how to retrieve the name of the algorithm used.
    String strAlgNameUsed = objAlg.AlgorithmName;

    // Determine whether the message length is a multiple of the block length.
    // This is not necessary for PKCS #7 algorithms which automatically pad the
    // message to an appropriate length.
    if (!strAlgName.Contains("PKCS7"))
       if ((buffMsg.Length % objAlg.BlockLength) != 0)
            throw new Exception("Message buffer length must be multiple of block length.");

    // Create a symmetric key.
    IBuffer keyMaterial = CryptographicBuffer.GenerateRandom(keyLength);
    key = objAlg.CreateSymmetricKey(keyMaterial);

    // CBC algorithms require an initialization vector. Here, a random
    // number is used for the vector.
    if (strAlgName.Contains("CBC"))
        iv = CryptographicBuffer.GenerateRandom(objAlg.BlockLength);

    // Encrypt the data and return.
    IBuffer buffEncrypt = CryptographicEngine.Encrypt(key, buffMsg, iv);
    return buffEncrypt;

Requirements (Windows 10 device family)

Device family


API contract

Windows.Foundation.UniversalApiContract, introduced version 1.0


Windows::Security::Cryptography::Core [C++]



Requirements (Windows 8.x and Windows Phone 8.x)

Minimum supported client

Windows 8

Minimum supported server

Windows Server 2012

Minimum supported phone

Windows Phone 8.1 [Windows Runtime apps only]


Windows::Security::Cryptography::Core [C++]



See also

Symmetric Key Encryption



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