2 posts • joined 14 May 2012
Re: The Code Book, by Simon Singh
"All ciphers are crackable, the pertinent question is how long it takes to crack the cipher."
Wrong! A one-time pad with a key from truly random data that is never re-used is impossible to crack. This is provable in a very simple way. A particular cipher-text can decrypt into any message of the given length. So even if you can cycle through every key and decrypt the message. You can't tell whether a message you get out is the right message. For example, if you encrypted a message, "The enemy is descending on our position" with one key, you could decrypt it with a different key and get, "The enemy is running away in disarray!!" There is no way, unless you actually have the real key, to know that you have the real message.
Even symmetric keys have limits to them. If you place a Dyson sphere around the sun to capture all energy it produces for the remainder of its life. And you also create a perfect counting state machine that uses a single quanta of energy to change state. There will be insufficient energy to count through all the keys of a 256 bit symmetric key algorithm. That's just counting the keys and doesn't include the problem of actually decrypting the message to test each time. So whilst theoretically true that "symmetric key ciphers can be cracked with enough time" the reality is, enough time often does not exist.
Re: It doesn't bode well...
Sometimes it is, sometimes not.
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