Re: [Full-disclosure] stealing ssh keys

["Raj Mathur (राज माथुर)" <raju@xxxxxxxxxxxxxxx>]

On Thursday 25 Oct 2012, Ivaylo Hubanov 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.

We're splitting hairs here :) but the private key is actually used to 
encrypt.  That encryption is called a signature.

Except, what you encrypt with the private key is a digest of the 
message, not the whole message itself.  When your recipient gets the 
message with the encrypted digest, she uses the same algorithm to make 
her own digest of the received message.  She then uses your public key 
to decrypt the encrypted digest you'd sent and compares the two digests.

If they're the same, then (a) the message originated from you, and (b) 
the message was not tampered with during transmission.

If they're not the same, then someone is playing silly buggers in the 
message flow.

Regards,

-- Raj
-- 
Raj Mathur                          || raju@xxxxxxxxxxxxx   || GPG:
http://otheronepercent.blogspot.com || http://kandalaya.org || CC68
It is the mind that moves           || http://schizoid.in   || D17F

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