SymmetricKeyAlgorithmProvider Class

Definition

Namespace:

Windows.Security.Cryptography.Core

Represents a provider of symmetric key algorithms. For more information, see Cryptographic keys.

public ref class SymmetricKeyAlgorithmProvider sealed

/// [Windows.Foundation.Metadata.ContractVersion(Windows.Foundation.UniversalApiContract, 65536)]
/// [Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
/// [Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
class SymmetricKeyAlgorithmProvider final

[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
[Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
[Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
public sealed class SymmetricKeyAlgorithmProvider

Public NotInheritable Class SymmetricKeyAlgorithmProvider

Inheritance

Object Platform::Object IInspectable SymmetricKeyAlgorithmProvider

Attributes

ContractVersionAttribute MarshalingBehaviorAttribute ThreadingAttribute

Windows requirements

Device family	Windows 10 (introduced in 10.0.10240.0)
API contract	Windows.Foundation.UniversalApiContract (introduced in v1.0)

Examples

using Windows.Security.Cryptography;
using Windows.Security.Cryptography.Core;
using Windows.Storage.Streams;

namespace SampleSymmetricKeyAlgorithmProvider
{
    sealed partial class SymmKeyAlgProviderApp : Application
    {
        public SymmKeyAlgProviderApp()
        {
            // Initialize the application.
            this.InitializeComponent();

            // Initialize the encryption process.
            String strMsg = "1234567812345678";     // Data to encrypt.
            String strAlgName = SymmetricAlgorithmNames.AesCbc;
            UInt32 keyLength = 32;                  // Length of the key, in bytes
            BinaryStringEncoding encoding;          // Binary encoding value
            IBuffer iv;                             // Initialization vector
            CryptographicKey key;                   // Symmetric key

            // Encrypt a message.
            IBuffer buffEncrypted = this.SampleCipherEncryption(
                strMsg,
                strAlgName,
                keyLength,
                out encoding,
                out iv,
                out key);

            // Decrypt a message.
            this.SampleCipherDecryption(
                strAlgName,
                buffEncrypted,
                iv,
                encoding,
                key);
        }

        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;
        }

        public void SampleCipherDecryption(
            String strAlgName,
            IBuffer buffEncrypt,
            IBuffer iv,
            BinaryStringEncoding encoding,
            CryptographicKey key)
        {
            // Declare a buffer to contain the decrypted data.
            IBuffer buffDecrypted;

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

            // The input key must be securely shared between the sender of the encrypted message
            // and the recipient. The initialization vector must also be shared but does not
            // need to be shared in a secure manner. If the sender encodes a message string 
            // to a buffer, the binary encoding method must also be shared with the recipient.
            buffDecrypted = CryptographicEngine.Decrypt(key, buffEncrypt, iv);

            // Convert the decrypted buffer to a string (for display). If the sender created the
            // original message buffer from a string, the sender must tell the recipient what 
            // BinaryStringEncoding value was used. Here, BinaryStringEncoding.Utf8 is used to
            // convert the message to a buffer before encryption and to convert the decrypted
            // buffer back to the original plaintext.
            String strDecrypted = CryptographicBuffer.ConvertBinaryToString(encoding, buffDecrypted);
        }
    }
}

Remarks

You create a SymmetricKeyAlgorithmProvider object by calling the static OpenAlgorithm method and specifying one of the following algorithm names.

• No padding:+ DES_CBC

• DES_ECB

• 3DES_CBC

• 3DES_ECB

• RC2_CBC

• RC2_ECB

• AES_CBC

• AES_ECB

• PKCS#7 block padding modes:+ AES_CBC_PKCS7

• AES_ECB_PKCS7

• DES_CBC_PKCS7

• DES_ECB_PKCS7

• 3DES_CBC_PKCS7

• 3DES_ECB_PKCS7

• RC2_CBC_PKCS7

• RC2_ECB_PKCS7

• Authenticated modes (see the EncryptedAndAuthenticatedData class):+ AES_GCM

• AES_CCM

• Stream Cipher:+ RC4

Properties

AlgorithmName	Gets the name of the open symmetric algorithm.
BlockLength	Gets the size, in bytes, of the cipher block for the open algorithm.

Methods

CreateSymmetricKey(IBuffer)	Creates a symmetric key.
OpenAlgorithm(String)	Creates an instance of the SymmetricKeyAlgorithmProvider class and opens the specified algorithm for use.

See also

• AsymmetricKeyAlgorithmProvider
• CryptographicEngine
• CryptographicKey