On Thu, Dec 08, 2005 at 03:33:40PM -0600, Chevalier, Victor T. wrote:
> I want to create a public key that is the same strength as the private
> key.
Game over, the above demonstrates sufficiently deep confusion about RSA,
that you must not proceed any further until you see why it is absurd.
> I need the public key to match the size constraints, as I am using then
> to encrypt and decrypt and when I try to use the public key the bioerr
> spits out"
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.
> When I run my code using openssl I am trying to decrypt using my public
> key,
> I get:
>
> 3500:error:0406506C:rsa routines:RSA_EAY_PRIVATE_DECRYPT:data greater
> than modlen:rsa_eay.c:308
>
> I want to decrypt with the public key.
>
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.
--
Viktor.
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