.NET (Core and Framework)

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Imports System.Security.Cryptography<br />
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        Public Function CreateSignature(ByVal strString As String) As Boolean<br />
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        'The exception occurs in the 'objCngKey = CngKey.Import' line on the bottom<br />
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        Dim data() As Byte<br />
        Dim bSignature() As Byte<br />
        Dim sSignature As String<br />
        Dim objCngKey As CngKey<br />
        Dim keyName As String = "ECDSA Key"<br />
        Dim publicKeyBytes(), privateKeyBytes() As Byte<br />
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        'Check if CngKey exists - if so, delete it, if not create a new pair of keys<br />
        If (CngKey.Exists(keyName)) Then<br />
            objCngKey = CngKey.Open(keyName)<br />
            objCngKey.Delete()<br />
        Else<br />
            Dim creationParameters = New CngKeyCreationParameters()<br />
            creationParameters.ExportPolicy = CngExportPolicies.AllowPlaintextExport<br />
            objCngKey = CngKey.Create(CngAlgorithm.ECDsaP256, keyName, creationParameters)<br />
        End If<br />
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        'Export the public and the private key to byte arrays<br />
        publicKeyBytes = objCngKey.Export(CngKeyBlobFormat.EccPublicBlob)<br />
        privateKeyBytes = objCngKey.Export(CngKeyBlobFormat.EccPrivateBlob)<br />
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        'Convert String to be signed to a byte array<br />
        data = System.Text.Encoding.Default.GetBytes(strString)<br />
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        'Create a ECDsaCng Object<br />
        Dim ecdsa As ECDsaCng = New ECDsaCng(objCngKey)<br />
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        'Sign the string<br />
        bSignature = ecdsa.SignData(data)<br />
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        'Convert Signature to Base64 string for better reading<br />
        sSignature = Convert.ToBase64String(bSignature)<br />
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        'Destroy Keypair<br />
        objCngKey.Delete()<br />
        objCngKey.Dispose()<br />
        ecdsa = Nothing<br />
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        'Re-Import the keys created above<br />
        'Actually the code below was part of another function, to which I pass the private key which was created by the code above<br />
        'The purpose of this was to sign another string with the same private key<br />
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        'Re-Import the previously exported public key - that works fine.<br />
        objCngKey = CngKey.Import(publicKeyBytes, CngKeyBlobFormat.EccPublicBlob) 'That works fine<br />
        'NOW, here's where the trouble starts:<br />
        '>>>>>>>>>><br />
        objCngKey = CngKey.Import(privateKeyBytes, CngKeyBlobFormat.EccPrivateBlob)<br />
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'Here a cryptographic exception occurs<br />
        '>>>>>>>>>><br />
        'Although I am re-importing the key exactly as exported above, a cryptographic exception occurs.<br />
        'What am I doing wrong? Importing the public key works fine, importing the private key fails...<br />
        'I also tried to only import the private key, without importing the public key, but that does not help either ...<br />
        'Is this a bug in the ECDsaCng function, or am I doing anything wrong?<br />
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    End Function<br />
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