Barack Obama

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visits member for 1 year, 5 months
seen Mar 4 '13 at 9:53

Feb
6
comment Is such a crypto-system available?
The question to which this is a good answer is quite far away from the initial question to which my answer was perfectly correct. Could you separate this into two questions for which yours would be the answer to one of them and mine the other?
Feb
6
comment Is such a crypto-system available?
@Eugen I must object to the goalpost shifting! I spent a fair amount of time checking that my solution solved your problem and then updating it after you changed the question once. Now you've changed it completely and it seems likely Poncho's answer will be better. It would have been fairer to accept my answer and then ask a new question with the "real" problem you were trying to solve all along!
Feb
5
comment What are some approaches to attack an triple key polyalphabetic cipher when the IV key and PT key are known?
The first keyed alphabet is **U P S T A I R B C D E F G H J K L M N O Q V W X Y Z **
Feb
5
comment What are some approaches to attack an triple key polyalphabetic cipher when the IV key and PT key are known?
The IV characters corresponding to the crib are "PIMA" yes? The crib row contents I have are P Y F R A B C D E G H I J K L M N O Q T U V W Z X S R T T <br/> I J K L M N O Q T U V W Z X S P Y F R A B C D E G H X H H <br/> M N O Q T U V W Z X S P Y F R A B C D E G H I J K L S E E <br/> A B C D E G H I J K L M N O Q T U V W Z X S P Y F R F Y Y <br/>
Feb
5
comment Generate random number which should depend on key
@fgrieu You're quite right. Although I'm sure it's more fun to pick holes in other people's answers than it is to craft your own, now you've already expended all this effort, why don't you craft a "proper" answer and see whether it gets accepted eh?
Feb
5
comment Is such a crypto-system available?
@poncho I guess I could have specified that D=E and then f is the inverse as you said.
Feb
5
comment Is such a crypto-system available?
@CodesInChaos 1)No. My definition of f is correct because the post specifies D(k_new,c2)=pt not E(k_new,c2)=pt. Presumably the Decryption function magically obtains the decryption exponent from k_new! 2)Give me an example of inverting f which is not equivalent to factoring the modulus and hence breaking RSA.
Feb
5
comment Generate random number which should depend on key
@fgrieu What you say is true. I forgot the lower bit would toggle and should have insisted on an odd $m$. However the level of my answer was appropriate for the question. We both know that any simple scheme based on a linear congruential generator is flawed and therefore "Streetboy" is not looking for something secure but needs instead to be told that he doesn't need to set m to 100 just because he needs numbers in that range. Now give me some upvotes!