Re: Using the Public Key embedded in the Assembly?

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• In reply to: Shawn Farkas [MS]: "RE: Using the Public Key embedded in the Assembly?"
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Date: Sat, 2 Oct 2004 15:56:20 +0200

Shawn
Thanks for your reply.
I am not sure if I follow you.
I have put the RSA keypair that I created via sn.exe on my machine in a
container: I used sn.exe -i [keyfile] [containername]. This made it possible
to create an RSACryptoProvider in a program on my machine to sign a license
file using my private key. The .snk file is used by the compiler to sign the
assembly and to embed the public key in the assembly.
When I send the assembly to a customer (together with the license file), the
assembly is only containing the public key, not the private key (I hope so!)
and no csp container with such name and content exists on the machine of the
customer. So to verify the signature, I need to transform the byte array I
get from [AssemblyName.GetPublicKey] in a useable form.
I don't understand how the StrongNameKeyInstall API can help me on the
machine of the customer: doesn't it need the .snk file (i.e. the keypair)?
Regards, Roland

""Shawn Farkas [MS]"" <shawnfa@online.microsoft.com> wrote in message
news:W64KMDAqEHA.3944@cpmsftngxa06.phx.gbl...
> Hi Roland,
>
> Instead of parsing the blob yourself, I would instead try to put it in a
> key container, and then use the RSACryptoServiceProvider constructor that
> reads keys out of containers. If you're on Whidbey, you can use the new
> ImportCspBlob method on RSACryptoServiceProvider, but if you're on Everett
> you'll have to do a little more work.
> You can use the exposed StrongNameKeyInstall API. You can find:
> * some details on using this API here:
> http://blogs.msdn.com/shawnfa/archive/2004/10/01/236773.aspx
> * the P/Invoke declaration for it here:
> http://blogs.msdn.com/shawnfa/articles/236725.aspx
> * and a sample of using it here;
> http://blogs.msdn.com/shawnfa/articles/236731.aspx
> Specifically, you'll want to look at the InstallKey method on line 149 of
> that last link.
>
> Once you've gotten a key into the key container, you can create a
> CspParameters object that specifies the key container name you installed

> to, and pass that object to the RSACryptoServiceProvider constructor.
>
> When you've finished your validation, the same links above will give a
> sample of the StrongNameKeyDelete API, which will remove the key
container.
>
> -Shawn
> http://blogs.msdn.com/shawnfa
> --
> This posting is provided "AS IS" with no warranties, and confers no
rights.
>
>
> Note:
> For the benefit of the community-at-large, all responses to this message
> are best directed to the newsgroup/thread from which they originated.
> --------------------
> > From: "roland" <roland.demeester@skynet.be>
> > Subject: Using the Public Key embedded in the Assembly?
> > Date: Fri, 1 Oct 2004 09:21:25 +0200
> > Lines: 48
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> >
> > L.S.
> > I want to build-in a license scheme in my controls.
> > The concept is to have the public key embedded im my assembly; a
> > licenseprovider then retrieves this public key and uses it to verify the
> > signature of the license file. The license file is unique to each
> licensee,
> > so if the license file is going astray, I always can trace the source.
> >
> > This is how I implemented this:
> >
> > I used sn.exe to create an RSA keypair that I refer to in my assembly
and
> I
> > stored this key pair (via sn. exe -i) in a named csp container. This
> embeds
> > the public key in my assembly. In my license file creation program I use
> an
> > RSACryptographicProvider based on cspParameters from this named
container.
> > During execution I retrieve the public key from the assembly through
> > [Assembly].GetExecutingAssembly().getName.getPublicKey. This gives me a
> byte
> > array, 160 long. The problem is that the methods for verifying the
> signature
> > in a signedXML document are using a RSACryptographicProvider and not
this
> > publicKey as a byte array. By browsing the user groups I found (was
> 'told')
> > that I can retrieve the modulus and the exponent from this byte array:
the
> > exponent should be equal to the last 3 elements and the modulus should
be
> > 128 elements long and starting at 27th element.
> > This should make it possible to create such a provider and use it to
> verify
> > the signature.
> > 'Create a new instance of RSACryptoServiceProvider.
> > Dim _rsa As RSACryptoServiceProvider = New RSACryptoServiceProvider
> > Dim _RSAKeyInfo As RSAParameters = New RSAParameters
> > 'Set _RSAKeyInfo to the public key values.
> > _RSAKeyInfo.Modulus = _modulus '(a byte array extracted from the
> publickey
> > array)
> > _RSAKeyInfo.Exponent = _exponent '(idem)
> > 'Import key parameters into the provider.
> > _rsa.ImportParameters(_RSAKeyInfo)
> > ...
> > return signedXml.CheckSignature(_rsa)
> > But this doesn't work!
> > When I extract the public key by using ToXMLString(False) in both cases,
I
> > get a totally different result for the public key: the modulus of the
> public
> > key retrieved from the csp container is only some 88 characters long,
> while
> > the one retrieved from the embedded public key in the assembly is some
160
> > characters long. Also the exponents are totally different (although
their
> > length is the same: 3).
> >
> > Obviously I am doing something wrong. Can anybody point me to the
> solution?
> > Thanks in advance.
> >
> > Roland
> >
> >
> >
>

• Previous message: roland: "Re: Using the Public Key embedded in the Assembly?"
• In reply to: Shawn Farkas [MS]: "RE: Using the Public Key embedded in the Assembly?"
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