How to Update particular Attribute after finding an object. getting error Method C_SetAttributeValue returned CKR_ATTRIBUTE_READ_ONLY

Question

I am trying to update an attribute after finding the object. Have tried out different cases.

My creation code:

using (var pkcs11 = new Pkcs11(@"C:\SoftHSM2\lib\softhsm2.dll", AppType.SingleThreaded))
{
    var slot = pkcs11.GetSlotList(SlotsType.WithTokenPresent)[0];
    using (var session = slot.OpenSession(SessionType.ReadWrite))
    {
        session.Login(CKU.CKU_USER, "1111");
        var objectAttributes = new List<ObjectAttribute>
        {
            new ObjectAttribute(CKA.CKA_CLASS, CKO.CKO_DATA),
            new ObjectAttribute(CKA.CKA_TOKEN, true),
            new ObjectAttribute(CKA.CKA_MODIFIABLE, true),
            new ObjectAttribute(CKA.CKA_APPLICATION, txtTypeofData.Text),
            new ObjectAttribute(CKA.CKA_LABEL,txtMsisdn.Text),
            new ObjectAttribute(CKA.CKA_VALUE, "Data object content original " + DateTime.Now)
        };
        var result = session.CreateObject(objectAttributes);
        session.Logout();
    }
}

My modifying code is:

using (Pkcs11 pkcs11 = new Pkcs11(@"C:\SoftHSM2\lib\softhsm2.dll", AppType.MultiThreaded))
{            
    var slot = pkcs11.GetSlotList(SlotsType.WithTokenPresent)[0];
    using (Session session = slot.OpenSession(SessionType.ReadWrite))
    {
        session.Login(CKU.CKU_USER, "1111");
        List<ObjectAttribute> objectAttributes = new List<ObjectAttribute>();
        objectAttributes.Add(new ObjectAttribute(CKA.CKA_CLASS, CKO.CKO_DATA));
        objectAttributes.Add(new ObjectAttribute(CKA.CKA_TOKEN, true));
        objectAttributes.Add(new ObjectAttribute(CKA.CKA_APPLICATION, txtTypeofData.Text));
        objectAttributes.Add(new ObjectAttribute(CKA.CKA_LABEL, txtMsisdn.Text));
        objectAttributes.Add(new ObjectAttribute(CKA.CKA_MODIFIABLE, true));

        var findA = session.FindAllObjects(objectAttributes);
        if(findA != null && findA.Count > 0)
        {
            List<ObjectAttribute> objectAttributesNew = new List<ObjectAttribute>();
            objectAttributesNew.Add(new ObjectAttribute(CKA.CKA_VALUE, "Data object content two changed " + DateTime.Now));
            session.SetAttributeValue(findA[0], objectAttributesNew);                        
        }                   
        session.Logout();
    }
}

Answer 1

The behavior you are observing seems to be specific to SoftHSM implementation. You can find following comment in its source code:

// NOTE: There is no mention in the PKCS#11 v2.40 spec that for a Data
//  Object the CKA_VALUE attribute may be modified after creation!
//  Therefore we assume it is not allowed to change the CKA_VALUE
//  attribute of a Data Object.