Error when signing a SHA256 Hash using Digital Certificate

Question

Is returning error from Invalid algorithm Specified, when it will be signed, how to proceed?

 Dim data = Encoding.UTF8.GetBytes(Me.txtCNPJEmpresa.Text + Me.txtCNPJSoftwareHouse.Text)
 Dim csp As RSACryptoServiceProvider = DirectCast(Certificado.PrivateKey, RSACryptoServiceProvider)

 Dim sha As SHA256 = SHA256Managed.Create()
 Dim hash As Byte() = New Byte() {}
 hash = sha.ComputeHash(data)

 Dim encrypted As Byte() = csp.SignHash(hash, "SHA256")

Answer 1

There are several possible causes; but the most common is when the certificate issued does not support the desired signature algorithm.

To check, open the certificate and select Detalhes. The following item must be present:

If necessary, re-issue the certificate with signature algorithm support SHA256.

Answer 2

Look at this simple example, running SHA256 directly in a text, debug the methods to add the certificate, in case, the certificate id right? to use as a keyword.

Private Function Encriptar(ByVal TextoEncriptar As String) As String
    Dim TextoEncriptado As String
    Dim TextoBytes() As Byte

    'Saber os Bytes do texto a encriptar
    TextoBytes = System.Text.Encoding.Unicode.GetBytes(TextoEncriptar)

    'Nova Instancia SHA256
    Dim HashSha As New SHA256Managed

    'Calcular hash do texto em bytes
    TextoBytes = HashSha.ComputeHash(TextoBytes)

    'Converter o array de bytes 
   TextoEncriptado  = Convert.ToBase64String(TextoBytes)


    Return TextoEncriptado 
  End Function

http://www.portugal-a-programar.pt/topic/18165-criptografia/

Answer 3

Try it like this.

Dim csp As SHA256 = Directcast(Certificate.Privatekey, Sha256cryptoserviceprovider)

I can’t test it now, but I think it’s conflicting with the application RSA x SHA256.