full-disclosure - Re: stealing ssh keys

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Date: Fri, 26 Oct 2012 12:58:37 -0700
From: "Thor (Hammer of God)" <thor@...merofgod.com>
To: Ivaylo Hubanov <sniffski@...il.com>
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>
Subject: Re: stealing ssh keys

Actually, the DSA key is used to sign the message in many applications, though I've often wondered exactly what reduction in security exists if the paired private key is used to sign material instead. Do you have any info on that?  I've asked industry leaders in crypto, and while they report it should be avoided, I've never received any quantified answer.

And just to make sure people understand (like the guy you replied to), the *message* is not encrypted with the pubic key - the *key the message is encrypted with* is encrypted with the public key.   While you CAN asymmetrically encrypt some data (116 bytes with a 1024 RSA key), it is the symmetric key (e.g. AES) which gets encrypted/decrypted with PKI keys and th AES key used to encrypt and decrypt the message itself. 

I'm sure you knew ht, but others obviously don't. :). 

Sent from whatever device will keep us from debating which one is better.

On Oct 24, 2012, at 11:51 PM, Ivaylo Hubanov <sniffski@...il.com> wrote:

> Yes Raj,
> You almost got the RSA encryption/decryption flow. :) Just the private key is used to sign the data and not to encrypt it. 
> Check this "http://en.wikipedia.org/wiki/Public-key_cryptography"
> Each user has a pair of cryptographic keys - a public encryption key and a private decryption key.
> ...
> The two main uses for public-key cryptography are:
> - Public-key encryption: a message encrypted with a recipient's public key cannot be decrypted by anyone except a possessor of the matching private key - it is presumed that this will be the owner of that key and the person associated with the public key used. This is used to attempt to ensure confidentiality.
> - Digital signatures: a message signed with a sender's private key can be verified by anyone who has access to the sender's public key, thereby proving that the sender had access to the private key and, therefore, is likely to be the person associated with the public key used. This also ensures that the message has not been tampered with (on the question of authenticity, see also message digest).
> 
> regards,
> sniffski
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