Re: Code Signing And Hacking

From: Andreas Hakansson (andreas.hakansson_at_nospam.com)
Date: 10/15/04 

Date: Fri, 15 Oct 2004 09:45:41 +0200

"Eugene Mayevski" <mayevski@eldos.org> skrev i meddelandet
news:uz$MggjsEHA.1468@TK2MSFTNGP12.phx.gbl...
> Hello!
> You wrote on Thu, 14 Oct 2004 10:53:32 -0700:
>
> V> 1. Is it possible to Recompile back into executable (since the original
> V> one was signed) and the hacker dont have a certificate?
>
> Yes.
>
> V> 2. If (1) is true, then would runtime detect that it has been hacked?
>
> No.
>
> Code signing is not aimed to protect you against the hacker, but to
> identify
> the vendor of the package. All in all, signing is signing and not
> encryption. If you want to protect the code, then start with obfuscation
> and
> see more specific topics about this.

Not quite sure, but if he is talking about strong naming then your statement
is
untrue. When you strong name an assembly, a SHA1 hash is created of your
assembly which in turn is encrypted with the private key. The encrypted hash
is then placed in your assembly along with the public key. These two
(encrypted
hash and public key) is refered to as a digital signature of your assembly.

Tampering would be impossible since when loaded, the CRL computes a SHA1
hash of the assembly, the public key is used to decrypt the encrypted hash,
created
when the assembly was signed. It then compares the two and determins if they
are
the same. If not then the CRL assumes it's been corrupted in some way
(tampering
being one possible explination).

So strong naming provides both a way of identifiying if the code is from a
specified
(and perhaps trusted) source as well as way to determin if it has been
tampered with.

> With best regards,
> Eugene Mayevski

HTH,

.Andreas

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