Re: Regarding public-private cryptograhic methods

From: Douglas A. Gwyn (DAGwyn_at_null.net)
Date: 05/12/03 

Date: Mon, 12 May 2003 18:15:24 GMT

pdqd wrote:
> 1. How exactly can someone break a private key? (I heard a lot about
> factorising the prime etc, but not sure how one can do that)

There are several PKCS; it sounds like you have RSA in mind.
For RSA, one of the two components of the public key is the product
of two primes, and a decryption key can readily be computed to
match the other component of the public key once the primes are known.
Therefore, if factoring an arbitrary product of two large primes
suddenly became feasible, so would computing private key
equivalents from RSA public keys.

> 2. If I have a large list of numbers along with the encrypted version
> of it (with my one private key), will the process of breaking my
> private key be easier for someone if he manages to get hold of that
> list?

Anybody can create such a list using the *public* key, so PKCS
would be useless if having such a list enabled cracking.

> And I always wanted to know what would be the best technique to
> exchange a confidential information between 2 parties (Is it RSA or
> some other?)

One would need to know *all* the relevant constraints. Generally
speaking it's not possible to be *sure* that some third party
cannot obtain the information, so all solutions involve trade-offs.

Relevant Pages

  • Re: Weak keys for RSA ?
    ... Robert D. Silverman RSA Public Key Validation, ... that p,q are so-called strong primes. ... outline how to guard against the Bach/Shallit ... a standard. ...
    (sci.crypt)
  • Need a bit help with decyphering a message
    ... not tell the encryption algorithm, so I decided to do a little ... I checked dozens of packets, and found out that the first 8 bytes are ... It is likely that they are primes, ... if it would be a Public Key). ...
    (sci.crypt)
  • Re: Need a bit help with decyphering a message
    ... which was "attila". ... not tell the encryption algorithm, so I decided to do a little ... It is likely that they are primes, ... if it would be a Public Key). ...
    (sci.crypt)
  • Re: SF: Back to theory
    ... you could pick up a pile of RSA challenge checks ... those upset with my saying special primes, ... Now if mathematicians were honest, good folk, who are sensible, as some ... If surrogate factoring gets quietly developed, ...
    (sci.math)
  • Re: SF: Back to theory
    ... you could pick up a pile of RSA challenge checks ... those upset with my saying special primes, ... Now if mathematicians were honest, good folk, who are sensible, as some ... If surrogate factoring gets quietly developed, ...
    (sci.crypt)
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