I read in Williams' book on truth that during the inquisition priests were eager to apply Kantian ethics under torture, and that this proved difficult because lies - and arguably secrets - were immoral.
Prima facie or indeed according to the literature may we keep a secret if we disagree with the methods of someone obtaining it? If so, may we promise to keep it, and would that mean we are obliged to? Finally, is that independent of any consequences of telling it?
If we promised to keep a secret we ought not to break it. This is another example of the categorical imperative.
Therefore, we should not lie to the torturer but explain to the torturer that 'I vowed to keep a secret and this is a promise I cannot break'.
In terms of the universalizability test (using hypothetical imperative), it would be 'to imagine a society in which everyone keeps the secrets as promised'. Can you imagine such a working society? Yes, without a doubt.
