encryption strength in bits

Discussion on encryption, data integrity, passwords, etc


encryption strength in bits

Postby insecurepc » Fri Apr 11, 2003 8:50 pm

It maybe in the links but I couldn't find it. If I could get a simple explanation of 56 bit and how it compares to 128 to 168 to 256 etc... I don't get it and just need a simple explanation.
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Postby kostyanj » Fri Apr 11, 2003 8:54 pm

Those are all different strengths of the keys.


How strong is a 128-bit key? For starters, a 128-bit key has 3.4 x 1038 possible values. That’s 1021 times stronger than a 56-bit DES key. The famous “DES Cracker” machines built in the late 1990’s could recover a 56-bit key in a matter of hours. If this time could subsequently be reduced to one second (meaning trying 255 keys per second), then it would take that same machine approximately 149 thousand-billion (149 trillion) years to crack a 128-bit key. To put this into perspective, the universe is believed to be less than 20 billion years old. Of course, if you need something stronger, SafeHouse still has you covered; offering two 256-bit ciphers and another at 448-bits.

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symmetric ciphers

Postby adfgvx » Sun Apr 13, 2003 2:35 am

You should, however, be wary of putting all your faith in key size. When considering a cyrptosystem, you should take lots of factors into consideration:

- How long has it been around? In other words, what is the liklyhood that an attack will be discovered aginst this cipher that is not yet known?

- Are there any known attacks? If so, do these "break" the cipher?

- How fast is it?

- What is the key length? Keep in mind a key length of 512 bits probably isn't appriciably more secure than one that is 256 bits long, since both are computational infeasable to brute force.

New ciphers like AES show a lot of promise, but they havn't been around as long as somthing like 3DES. So, in the end, it's a compromise. For all you know, the NSA has already discovered a flaw in AES that the acedemic community has yet to uncover.
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