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  1. Senior Member /usr's Avatar
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    #1

    Default ...bit encryption?

    Could someone explain this a bit more? I understand the higher bit, the better the security and the harder it is to break, but what exactly does 128-bit, 40-bit, and all that mean? Sorry if the questions sounds too simple. The book I have has yet to explain it and I've got to know.
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    #2
    Well, I know very little about encrytion except that it's a method of guaranteeing protection of transmitted data against theft and/or alteration.

    I think that you want to know why the more bits the better.
    I do understand that.

    Generally when you talk about bits, you're talking about serial transmission and you talk bytes when your working parallel. Ethernet, Token-ring, Internet all work serially--bits get transferred one right after the other in a cute little row. It's like marbles rolling through an inclined tube. If the tube is at the proper diameter, once the marble starts rolling the next marble can't get ahead of the one in front of it, neither can it jump back behind the one behind it. The marbles always maintain their position while in the transmission state in the tube. And, for this to work, each marble will be either black or white(representing on or off).

    Now say in order to get into a restaurant for lunch you have to roll your marbles down your own particular tube to open the door. If you don't have each black or white marble in the proper position the door won't open and you won't get to eat lunch.

    Now, the advantage of lots-o'-bits works because the system is binary--only 2 values possible for each bit, on or off and the more possible combinations of bits that you have. That's what makes it work--combinations. E.g.,

    40 bit combos=2^40 = 1099511627776 possible combos
    128 bit combos=2^128 = 3.4 X 10^38(My calculator absolutely refused to display this as a simple number because it's ridiculous!)

    Anyway I'm pretty sure about this. But, you can see the seemingly infinite possibilities of combinations--script kiddies and seasoned crackers tremble. You can, theoretically, never crack these combos--too big.

    This is where I end. I don't know if this principle is applied to actual data, or if it's the method of supplying a key to get access to the data, but I think were talking about the key here.

    I'm sure that someone is going to add to this who has a much better grasp of things.

    Hope this is what you're looking for.
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  4. Senior Member /usr's Avatar
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    #3
    That helped, but I'm not sure how to word exactly what I'm asking. What does 128-bit encryption do to something that it is encrypted? How does it work? How does the 128 bit relate to the changing of the data? Or is it like you said, and there are just that many combinations of changing the data?

    And yes, that number is absolutely huge. Calculators won't display it, as it has around 6 or 7 sets of zero's. I only know because I saw it yesterday when we went over IPv6 in class.
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  5. Senior Member
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    #4
    Try this site.

    http://www.insanemind.co.uk/hispec/encryption.htm

    There is even an option to create an example.

    I understand a little more now. Somehow the encrytion program(?) uses an algorithm to scramble the data(text or whatever) by employing the key that we are talking about. Guess the size of the key actually determines just how radical the scrambling is.

    My marble example is not really applicable(guess I "lost my marbles" this time). But you still have to have the key, but it doesn't acheive its purpose in the way that I envisioned.

    Anyway, I'm going to put link on this site and get back to it sometime.

    Hope this helps.
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  6. Certification Invigilator Forum Admin JDMurray's Avatar
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    #5
    The longer the key the more difficult it is to break with a brute-force attack. For example, a 24-bit key has 16 million possible combinations, while a 56-bit key has 72 quadrillion possible combos. The trade-off is that shorter keys use fewer CPU cycles, but are easier to crack. Also, longer keys do not produce more cypher-text than shorter keys.

    Here's a good paper on the subject: http://www.giac.org/practical/gsec/L...liams_GSEC.pdf
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  7. Junior Member
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    The example is screwed up ... http://www.insanemind.co.uk/hispec/encryptexample.htm
    Try:
    Key= 0 (as in zero)
    Plain text= a

    or even put nothing in the Key field...
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    #7
    Thanks for the word on the example. I thought something was screwy.
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    #8
    Quote Originally Posted by LostInSpace
    What does 128-bit encryption do to something that it is encrypted? How does it work? How does the 128 bit relate to the changing of the data?
    The basic idea is this. You have your 128 bit key, and a lot of data. You split the data in 128 bit chunks. You take the first chunk, and you XOR it with the key; you got an encrypted first chunk. Then you take the second chunk and XOR it with the key; got the encrypted second chunk. Keep going until you encrypt all the chunks. Then you concatenate the encrypted chunks, and bingo, you got your encrypted data. Decryption is the same: split the encrypted data in 128 bit chunks, XOR each chunk with the key, etc.

    There are many variations of this scheme, but at its simplest, that is it.
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    #9
    Great example (directly above) on how the key can be used. Going a little deeper explains that there are many algorithms out there that use the key in different ways. The key 26, 40, 128, 256 bits and etc, is injected into the algorithm to be used in a calculation that will scramble the results. The algorithm can be any combination of substitution (mapped into a different item) and/or transposition (change the position)

    (Using only substitution) It is like this 1+3=4
    and you want to hide the answer (4). So you substitute the (3) by using a substitution algorithm with a 1 bit key to scramble the (3). The one bit key gives the algorithm directions to follow one (1 bit) of a number of particular options:
    1. Substitute the #3 with another number, one (1bit) increment higher
    2. Substitute the #3 with another number, one (1bit) increment lower
    3. Put the #3 through a scrambling calculation (a sub-algorithm) (1) time
    (if it was a 2bit key then there would be a choice of 1 or a combination of 2 of the above or more options)
    By substituting the #3 with a different number (say a 4; which would be incrementing the 3 by 1) you have effectively masked (encrypted) the answer
    1+4=5

    You will perform the same using a reverse algorithm to un-mask (un-encrypt) the answer.

    Now imagine the options that can be generated with not only substitution but also transposition as you increase the key size from (1) to 2, 4, 8 ...128. Also think about the possibilities when you include a larger key space (characters that can be used) from 0-9 to zero-through-letter Z.

    XORing is a simple substitution algorithm

    Summary and quote from "Network Security Essentials" by William Stallings
    - Encryption Algorithm: the encryption algorithm performs various substitutions and transformations on the plaintext
    - Secret Key: The secret key is input to the algorithm. The exact substitutions and transformations performed by the algorithm depend on the key. [Which will be a particular size in terms of bits]

    A side bar is that cryptography key size helps determine a level of algorithm strength. The algorithms are actually classified by 3 different dimensions in terms of processing and using the key. They are:
    (1) Types of operations - substitution or transposition
    (2) Number of keys used - 1 key=symmetric 2 keys=asymmetric or public key
    (3) Plaintext processing - block cipher: such as encrypting 64 bits of a message at a time or stream cipher: encrypting one bit or element at a time

    And all of these fall into how the 128bit key would be used in the algorithm to perform encryption

    Hope some of this helps with the thread.

    - jtb
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