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DSACryptoServiceProvider Class

Updated: May 2009

Defines a wrapper object to access the cryptographic service provider (CSP) implementation of the DSA algorithm. This class cannot be inherited.

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

'Declaration
<ComVisibleAttribute(True)> _
Public NotInheritable Class DSACryptoServiceProvider _
	Inherits DSA _
	Implements ICspAsymmetricAlgorithm
'Usage
Dim instance As DSACryptoServiceProvider

You can use the DSACryptoServiceProvider class to create digital signatures and protect the integrity of your data.

To use a public-key system to digitally sign a message, the sender first applies a hash function to the message to create a message digest. The sender then encrypts the message digest with the sender's private key to create the sender's personal signature. Upon receiving the message and signature, the receiver decrypts the signature using the sender's public key to recover the message digest and hashes the message using the same hash algorithm that the sender used. If the message digest that the receiver computes exactly matches the message digest received from the sender, the receiver can be sure that the message was not altered while in transit. Note that a signature can be verified by anyone, because the sender's public key is common knowledge.

This algorithm supports key lengths from 512 bits to 1024 bits in increments of 64 bits.

Important noteImportant Note:

You should ensure that IDisposable is called when you are finished with the DSACryptoServiceProvider. To do this, instantiate the object in a using statement; for example, using (DSACryptoServiceProvider DSA = new DSACryptoServiceProvider()). For more information about the using statement, see using Statement (C# Reference) or Using Statement (Visual Basic).

The following code example creates a digital signature of a hash value using the DSACryptoServiceProvider class and then verifies the signature.

Imports System
Imports System.Security.Cryptography

Public Class DSACSPSample
    Public Shared Sub Main()
        Try 
            Dim privateKeyInfo As DSAParameters
            Dim publicKeyInfo As DSAParameters

            ' Create a new instance of DSACryptoServiceProvider to generate 
            ' a new key pair. 
            Using DSA As New DSACryptoServiceProvider()
                privateKeyInfo = DSA.ExportParameters(True)
                publicKeyInfo = DSA.ExportParameters(False)
            End Using 

            ' The hash value to sign. 
            Dim HashValue As Byte() = _
                { 59, 4, 248, 102, 77, 97, 142, 201, 210, 12, 224, _
                93, 25, 41, 100, 197, 213, 134, 130, 135}

            'The value to hold the signed value. 
            Dim SignedHashValue As Byte() = DSASignHash(HashValue, privateKeyInfo, "SHA1")

            ' Verify the hash and display the results. 
            Dim verified As Boolean = DSAVerifyHash(HashValue, SignedHashValue, publicKeyInfo, "SHA1")

            If verified Then
                Console.WriteLine("The hash value was verified.")
            Else
                Console.WriteLine("The hash value was not verified.")
            End If 
        Catch e As ArgumentNullException
            Console.WriteLine(e.Message)
        End Try 
    End Sub 

    Public Shared Function DSASignHash(HashToSign As Byte(), DSAKeyInfo As DSAParameters, _
        HashAlg As String) As Byte()
        Dim sig As Byte() = Nothing 

        Try 
            ' Create a new instance of DSACryptoServiceProvider. 
            Using DSA As New DSACryptoServiceProvider()
                'Import the key information.
                DSA.ImportParameters(DSAKeyInfo)

                ' Create an DSASignatureFormatter object and pass it the 
                ' DSACryptoServiceProvider to transfer the private key. 
                Dim DSAFormatter As New DSASignatureFormatter(DSA)

                ' Set the hash algorithm to the passed value.
                DSAFormatter.SetHashAlgorithm(HashAlg)

                ' Create a signature for HashValue and return it.
                sig = DSAFormatter.CreateSignature(HashToSign)
            End Using 
        Catch e As CryptographicException
            Console.WriteLine(e.Message)
        End Try 

        Return sig
    End Function 

    Public Shared Function DSAVerifyHash(HashValue As Byte(), SignedHashValue As Byte(), _
        DSAKeyInfo As DSAParameters, HashAlg As String) As Boolean 
        Dim verified As Boolean = False 

        Try 
            ' Create a new instance of DSACryptoServiceProvider. 
            Using DSA As New DSACryptoServiceProvider()
                ' Import the key information.
                DSA.ImportParameters(DSAKeyInfo)

                ' Create an DSASignatureDeformatter object and pass it the 
                ' DSACryptoServiceProvider to transfer the private key. 
                Dim DSADeformatter As New DSASignatureDeformatter(DSA)

                ' Set the hash algorithm to the passed value.
                DSADeformatter.SetHashAlgorithm(HashAlg)

                ' Verify signature and return the result.
                verified = DSADeformatter.VerifySignature(HashValue, SignedHashValue)
            End Using 
        Catch e As CryptographicException
            Console.WriteLine(e.Message)
        End Try 

        Return verified
    End Function 
End Class

System.Object
  System.Security.Cryptography.AsymmetricAlgorithm
    System.Security.Cryptography.DSA
      System.Security.Cryptography.DSACryptoServiceProvider

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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

.NET Framework

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

.NET Compact Framework

Supported in: 3.5, 2.0

Date

History

Reason

May 2009

Added a note about ensuring that IDisposable is called after you use this class.

Information enhancement.

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