Re: searching for encrypted fields in data columns

On Tue, 09 Mar 2004 07:04:04 GMT, Chris <chris2k01_at_hotmail.com> wrote:

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>Steve Jorgensen wrote:
>
><snip>
>> If you use PKI-style encryption, you can make the encryption key
>> public, and
>> the decryption key private. This way, you can encrypt a card
>> number, then do
>> a search for a match on that value. Since the card number will
>> encrypt identically each time, the search will match.
><snip>
>
>Hi,
>As a matter of fact, your assumption is not quite true. While there
>are asymmetric encryption algorithms that *do* output the same
>ciphertext for a certain plaintext with a certain key, most are not
>like that, at least not most secure implementations. For example,
>using RSA, padding is almost always applied to the plaintext before
>encryption. This padding serves multiple purposes: it expands the
>plaintext to the correct length, it can (in some cases) catch a
>faulty decryption, and it prevents the same ciphertext from resulting
>from the same plaintext. The padding is random within a set of rules,
>thus introducing a small amount of random plaintext into the mixture.
>This plaintext basically randomizes the whole ciphertext, making it
>impossible to search in this way.

Yes, but if searching is required, a PKI system without padding could be used. Of course, that has all the security weaknesses that you and I have both suggested.

...
>If we're talking about credit card numbers, I'd like to think they're
>being stored with top-of-the-line encryption here, which would by
>nature include padding or feedback of some type.

Right, and that means you can't search for them. The very act of having them be searchable by card number by any means makes the system vulnerable. Received on Tue Mar 09 2004 - 01:35:52 CST