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Old 2016-01-30, 23:07   #1
Jan 2016

1 Posts
Default RSA multi factor

i have used the YaFu and entered a N of an RSA and it solved it by giving me back 15 primes... how can i continue from this point on to break the small RSA key that i have ?
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Old 2016-01-30, 23:19   #2
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Mini-Geek's Avatar
"Tim Sorbera"
Aug 2006
San Antonio, TX USA

17·251 Posts

Are you sure you've got the right N? Any good key choice (if not any valid key, if this article's offhand comment is right) will be a semiprime, not consist of 15 primes.

Anyway, once you've got the right number factored, this post from StackOverflow goes into (the mathematical side, not a script or anything) how to calculate the private key. The most important part is this: (d is the private exponent, e is the public exponent, n is the public key, n is semiprime with factors p and q)

d = e^-1 mod phi(n)
  = e^-1 mod (p-1)*(q-1)
(note that if you don't have a semiprime, the phi calculation gets more complicated)

Then you just need to compute that modular multiplicative inverse, convert the number into a usable format (hex?) and use it.

Last fiddled with by Mini-Geek on 2016-01-30 at 23:28
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Old 2016-01-30, 23:25   #3
I moo ablest echo power!
wombatman's Avatar
May 2013

6CD16 Posts

Sounds like a Teslacrypt infection. You may wish to head over here if that's the case:
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