full-disclosure - question regarding RSA

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Date: Mon, 30 Aug 2010 21:32:06 -0500
From: jf@...s74ur.corenetworks.net
To: full-disclosure@...ts.grok.org.uk
Subject: question regarding RSA

Hi,

i'm not really a crypto guy and I'm having problems explaining something; basically my understanding of RSA PKI is that the padding bytes are added because RSA is a deterministic algorithm and that without the padding an attacker with knowledge of the plaintext and access to the resultant ciphertext can significantly reduce the keyspace in deducing the private key, but the question is by how much? Assuming the absence of OAEP/et al, is it realistic to expect one to be able to brute force this keyspace? Theres really no documentation on the subject because well RSA is not expected to be secure in this environment, even though its deployeed this way more often than expected.

I'm trying to write up a test to do this, but I'm running into the problem that I'm having to modify what simplified implementations I can find to make sure no padding (or attacker controlled padding) exists, and therefore I'm gonna have the problem of either modifying something i didnt mean to, or more likely having the results discarded because it was my own implementation.

So, what I'm hoping for is someone with a fairly in-depth knowledge of RSAES-OAEP who can tell me what the reduction in complexity would be given an attacker that can control the plain-text, can receive the ciphertext, and can control the variables associated with OAEP; they just dont have access to the private key.

Thanks.
jf

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