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What is Cryptanalysis?

By Dan Blacharski
Updated May 17, 2024
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Cryptanalysis is the study of taking encrypted data, and trying to unencrypt it without use of the key. The other side of cryptography, it is used to break codes by finding weaknesses within them. In addition to being used by hackers with bad intentions, this discipline is also often used by the military. It is also appropriately used by designers of encryption systems to find, and subsequently correct, any weaknesses that may exist in the system under design.

There are several types of attacks that a cryptanalyst may use to break a code, depending on how much information he or she has. A ciphertext-only attack is one where the analyst has a piece of ciphertext (text that has already been encrypted), with no plaintext (unencrypted text). This is probably the most difficult type of cryptanalysis, and calls for a bit of guesswork. In a known-plaintext attack, the analyst has both a piece of ciphertext and the corresponding piece of plaintext.

Other types of attacks may involve trying to derive a key through trickery or theft, such as in the "man-in-the-middle" attack. In this method, the cryptanalyst places a piece of surveillance software in between two parties that communicate. When the parties' keys are exchanged for secure communication, they exchange their keys with the attacker instead of each other.

The ultimate goal of the cryptanalyst is to derive the key so that all ciphertext can be easily deciphered. A brute-force attack is one way of doing so. In this type of attack, the cryptanalyst tries every possible combination until the correct key is identified. Although using longer keys make the derivation less statistically likely to be successful, faster computers continue to make brute-force attacks feasible. Networking a set of computers together in a grid combines their strength, and their cumulative power can be used to break long keys. The longest keys used, 128-bit keys, remain the strongest, and less likely to be subject to this type of attack.

At its core, cryptanalysis is a science of mathematics, probability, and fast computers. Cryptanalysts also usually require some persistence, intuition, guesswork and some general knowledge of the target. The field also has an interesting historical element; the famous Enigma machine, used by the Germans to send secret messages, was ultimately cracked by members of the Polish resistance and transferred to the British.

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Discussion Comments

By bagley79 — On Nov 29, 2012

As computers continue to get faster, I think it will be easier instead of more difficult for information to get into the wrong hands. I have had my computer hacked into, and if that ever happens to you, one thing is for sure, you sure take different measures to try and protect your information. I guess I could refuse to use a computer, but don't really know if that would be any better or not.

By julies — On Nov 29, 2012

My nephew is a computer genius. This is something he has been able to do since he was young and his mind just naturally understands how computers work. He can hack into just about any system and that is kind of scary.

The positive side of this is that his ability can be used for good. Companies need people with his ability to offset those hackers who use their skills to steal information from people.

I have no clue how cryptanalysis works. I think the majority of people are like me, and think that just because a website is secure, you are safe. There is a lot that goes on behind the scenes that I don't understand, yet I feel comfortable enough to continue entering personal information online.

By John57 — On Nov 28, 2012

I try to take the proper precautions to prevent hackers from breaking into my computer system. When I think about all the personal information I have stored on my computer, it can make me pretty nervous thinking about someone having access to all that information.

I have read somewhere that some hackers can break into your computer just by following the keystrokes you make on your keyboard. That sounds pretty creepy to me.

Even by changing passwords on a regular basis and making sure I have a firewall, I know it is possible for the right person to get at my information.

By honeybees — On Nov 27, 2012

Although I don't understand much about cryptanalysis, I am somewhat fascinated by it. It amazes me how people who know what they are doing can break a code and get at valuable information that was supposed to be safe. Even though modern cryptanalysis has come along way from where it used to be, the concept is still the same.

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