With RSA keys, the private key d must remain private. If the public key e is very small, this is not completely possible. This exercise demonstrates how simple it is to compute a portion of the secret key d.
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I think I found the d' but I can not submit it in correct format.
Should it be submitted as a sequence of 510 "0" and "1" or we should pad it with two "0" on the left or to pad it also on the right to make its length equal to 1024?

Ha, ha, that's why it's level II.....:)

Victor, the task: find the INTEGER value d' that approximates d for exactly 510 bits.

EDIT: looked into the challenge myself and I know understand your question Victor.

it is very confusing, what exactly d' is. it occurs in the text of the challenge, but it is never defined.

can someone specify, what d' is, resp. clearify, how the solution should look like?

best regards,
jomandi

p.s.: in the hall of fame the number of the remaining trials for a challenge is wrong. i sended 2 of 15 possible attempts for this challenge, so i have to have 13 trials left. but the site writes:

Level II - Partial Key Exposure with RSA – Part 1 - Last attempt: 2012-02-07 (21:06:53) - 2 trials left

so obviously it counts in the wrong direction.

I have returned lol.

I think this challenge is ambiguous...it doesn't say how we have to approximate. Do we match up the left most 510 bits of d or the right most?

it is unique, where the 510 matching bits are, so this is not the problem.

i have the two possible approximations of d, which are mentioned in the challenge, so i also know the greater one.

the problem is, that i do not know, what they expect as solution.

i have tested the most probable "solutions" but none of them have been accepted.

I have never really considered a problem like this before so I might have got confused. I don't see a way to find d' without using its relationship with d...and that depends on whether it shares the right hand bits or the left hand bits with d.

Isn't that nice. The more wrong answers you give, the more chances you get ...


If this were my challenge and I'd uploaded it only this afternoon I would be keen to see the reactions so I could give a reply when needed !

I really wish they would standardize that every problem must have a keyword for a solution instead of entering hundreds of characters into a 20 character text box. That would simplify it for the solvers as well as the puzzle makers.

For example, in this problem instead of having to explain about multiple d's so pick the larger one and then type in 510 1s and 0s there could be a ciphertext. The right key would decrypt it, and it would say what keyword to enter as the solution. No explanation about picking the right d' needed as only the right one would work, no grumbling in the forums about answer format as there would be no format.