On Fri, Dec 09, 2005 at 07:25:12AM +0100, [EMAIL PROTECTED] wrote:
> >RSA Public and private keys are not used to encrypt arbitrary data, there
> >are many complex traps to avoid because RSA is a commutative group. You
> >use RSA private keys to sign carefully constructed message digests that
> >avoid the various chosen plain-text attacks on RSA. You use RSA public
> >keys to encrypt randomly generated session keys that in turn encrypt
> >the message contents. All this specificed in carefully designed PKCS#N
> >standards that describe correct standard use-cases of RSA cryptography.
> >
> >The public key is not suitable for decryption, it is only suitable for
> >signature verification. Decryption is only possible with the private
> >key and only if chosen-plaintext/chose-ciphertext attacks are carefully
> >avoided.
>
> Hummm.... Victor ?
>
> You can cipher and decipher what you want as well as with a RSA public
> and private keys ;-)
>
> If you cipher with the public key you have to use the private associate
> key of course and vice versa.
>
Yes the bit patterns of the two keys are mathematical inverses, but
that is not significant. Decryption (rather than signature verification)
with a *public* key makes no sense. Also RSA is never used as a bulk
cipher, the chosen-plaintext and chosen-ciphertext attacks are not mere
theoretical musings.
Yes, the bignum value of the public key can be recast as a private key
whose public key has the bits of the original private key. Mathematically
these may be the same, but they are rather different as typed data
structures, one is a public key and the other is a private key. You
use public keys to encrypt and verify and private keys to decrypt and
sign. In all cases appropriate care is required to avoid falling prey
to chosen-<mumble>text attacks.
--
Viktor.
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