1

I'm confused by the meaning of or in this sentence:

Encryption poses a problem for intelligence agencies by scrambling data with a secret code so that even if they, or any other third-party, manages to capture it, they cannot read it—unless they possess the key to decrypt it or have the ability to crack the encryption scheme.

Source

If we look at these example usages of or:

A. I don't like apples or oranges.

B. I ignored it not simply because I was sick or I didn't care about it.

In both these sentences, the or implies that neither of the options are right. In the case of A, I like neither apples nor oranges. In the case of B, neither because I was sick nor because I didn't care about it. (They are both wrong.)

However, in the excerpt above, it doesn't sound like this is true. If I apply the interpretation above to the part containing "or" here, it would mean that they would have to have both the key to decrypt it and have the ability to crack the encryption. Because "unless they possess the key or have the ability" means "if they don't possess the key or have the ability," which means that this or the rule applied above transferred to this as well, would mean the aforementioned.

What's going on here?

  • What's throwing you off is that, in your sample usages, you are using a NOT. Try samples without a not, like: "I would like an apple or an orange" (which means you'd like to have either one, but not necessarily both), or "We want to paint the room blue or yellow" (so, either a can of blue paint or a can of yellow paint will meet our needs). When you mix negation with logic, odd things happen. – J.R. Sep 9 '13 at 1:22
3

The combination of or or and with a negation in natural language doesn't always make sense if you try to parse the sentence like a mathematical formula. However, in the case of unless, you can parse the sentence reliably. “Unless X” means “if X is not true”, even when X contains a conjunction or a disjunction.

“They cannot read it, unless they possess the key to decrypt it or have the ability to crack the encryption scheme.” =
* “They cannot read it if not (they possess the key to decrypt it or have the ability to crack the encryption scheme).” =
“They cannot read it if they neither possess the key to decrypt it nor have the ability to crack the encryption scheme.” =
“They cannot read it, if they don't possess the key to decrypt it and don't have the ability to crack the encryption scheme.”

  • So you mean, you need both the key to decrypt and the ability to crack the encryption? – user2492 Sep 8 '13 at 22:34
  • @kih1930 No, it's the opposite: if they possess the key or the ability to crack the encryption scheme, then they can read the data – Gilles 'SO- stop being evil' Sep 8 '13 at 22:40
  • So if they have neither A nor B, they can't do C. It means if they have either A or B, they can do C? Am I right? So is my interpretation of the A and B sentences is correct? – user2492 Sep 8 '13 at 22:43
  • 2
    @kih1930 At this point, I'm not sure whether you have a problem with English or with logic or with cryptography. Yes, if they have either A or B, they can do C. If they have neither A nor B, they can't do C. – Gilles 'SO- stop being evil' Sep 8 '13 at 22:46
5

You're comparing, well, apples and oranges, a bit. (Sorry, had to do that.)

I know the sentence says "they can't read it", but that's before the "unless". The "unless" makes it a positive statement, so it's no longer an example of "I don't like apples or oranges". Instead, it's like "I can get there by bike or by bus." If either of the options is true/available, then I can get there.

Another reason you might be having trouble parsing the sentence is that there's a bit of ellipsis going on. If we put in the omitted pronoun, the structure is a bit easier to see.

Encryption poses a problem for intelligence agencies by scrambling data with a secret code so that even if they, or any other third-party, manages to capture it, they cannot read it—unless they possess the key to decrypt it or [they] have the ability to crack the encryption scheme.

So, encrypted data is generally unreadable. However, if you possess the decryption key, OR if you have the ability to crack the encryption scheme, then you can read it.

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