Almost all security systems in the modern world rely on a shared secret (password) system of some kind. The premise is that no-one other than the account holder knows the secret, so anyone who knows the secret must be the account holder!

Is there a basis in Halacha for using a piece of secret information to establish credibility (נאמנות)? I am looking for answers based on the rules of נאמנות only which do not rely on extra agreements between the parties.

Here are a few example cases where this would make a difference:

  1. A Jewish bank offering online money transfer to Jewish customers. What if the customer claims he never signed on and requested the money transfer?
  2. Sending online payments to a Jewish vendor. What if the vendor claims you sent it to the wrong place?
  3. Trusting a Psak from an authority which is already נאמן. For example, if I receive an e-mail from a someone claiming to be R' Chaim Kanievsky שליט''א (or his agent) and I want to verify it. (You can use secure hashes to verify identity, they work like passwords).
  4. ... lots more
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    Can you give an example where this would be useful? – Double AA Mar 25 '15 at 18:50
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    Why would you think they can't? The customer agreed to those terms of service presumably – Double AA Mar 25 '15 at 18:55
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    @DoubleAA How about shelichus for a get, or similar? – Ypnypn Mar 25 '15 at 18:58
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    Ploni, welcome to Mi Yodeya, and thanks for bringing your question here! As @DoubleAA indicates, it will be a much stronger question if you edit in some suggestions for realms of Halacha or particular cases in which password-based trust may matter. Please consider registering your account, which will give you access to more of the site's features. – Isaac Moses Mar 25 '15 at 19:00
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