I am trying to decrypt an XML package that was encrypted by a SHA-256 certificate. So far, any examples have focused on SHA-1.

As directed in this post, I have created a CK_RSA_PKCS_OAEP_PARAMS struct type, and populated it with the SHA-256 algorithms.

Unfortunately, calling the session's DecryptInit() with the CKM_RSA_PKCS_OAEP mechanism and its parameters always returns error code 13 (CKR_MECHANISM_PARAM_INVALID). This occurs whether I use SHA-256 or the SHA-1 sample provided in the post linked above.

Here are the relevant sections of code:

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[StructLayout(LayoutKind.Sequential, Pack = 0, CharSet = CharSet.Unicode)]
public struct CK_RSA_PKCS_OAEP_PARAMS
{
    public ulong HashAlg;

    public ulong Mgf;

    public ulong Source;

    public IntPtr SourceData;

    public uint SourceDataLen;
}

...

Mechanism mech = new Mechanism(Mechanism.CKM_RSA_PKCS_OAEP, new CK_RSA_PKCS_OAEP_PARAMS()
{
    HashAlg = Mechanism.CKM_SHA256,
    Mgf = Mechanism.CKG_MGF1_SHA256,
    Source = 1,
    SourceData = IntPtr.Zero,
    SourceDataLen = 0,
});

_session.DecryptInit(mech, privateKey); // This returns code 113

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