"Gary Bond" wrote:

> HI All,
>
> Could I ask for some help with RSACryptoServiceProvider class. I am trying
> to write 3 small apps to demonstrate RSA encryption, and giving out a public
> key as an xml string. One app makes the xml key strings and saves them as
> files, and the other 2 apps encrypt and decrypt, using those xml strings.
>
> 1) I make the keys like this, using code from MSDN
>
>         Dim cp As CspParameters = New CspParameters()
>         cp.Flags = CspProviderFlags.UseMachineKeyStore
>         Dim RSA As RSACryptoServiceProvider = New
> RSACryptoServiceProvider(2048, cp)
>         Dim PubKey as string = RSA.ToXmlString(False)
>         Dim PrivateKey as string = RSA.ToXmlString(True)
>     'subsequently save these strings to file
>
> Do I need to initialise the CspParameters and use it in the creation of the
> RSACryptoServiceProvider? Could I just use the parameterless constructor on
> the RSACryptoServiceProvider to give me a new instance, and then save the
> public + private xml keystrings, like this
>
>         Dim RSA As RSACryptoServiceProvider = New
> RSACryptoServiceProvider(2048)
>
>
> If I have to use the CspParameters, since I am saving the xml strings for
> later use, do I have to set the UseMachineKeyStore? Would this code work if I
> move the exe's to another machine in either case. The idea of these apps is
> that I give out the public key string file and the encryptor, someone else
> encrypts some stuff for me at a remote location, and then I decrypt the file
> they send me with my private key.
>
>
> 2) When encrypting, if I try to encrypt a large string of 'stuff', I get a
> cryptographic error "Key not valid for use in specified state". Heres the
> code from the function:
>
>             Dim RSA As New RSACryptoServiceProvider
>             RSA.FromXmlString(XMLKey)
>             Return RSA.Encrypt(DataToEncrypt, False)
>
>
> where XMLKey is the public xml key string from point 1) above, previously
> saved and re-opened on my hard drive.
>
> If I encrypt a small amount of data all goes well and I can decrypt later on
> with
>
>     Dim RSA As New RSACryptoServiceProvider()
>         RSA.FromXmlString(XMLKey)
>         ClearTxt = RSA.Decrypt(BytesToDecrypt, False)
>         Return Encoding.ASCII.GetString(ClearTxt)
>
> As you can tell I am very inexperienced with encryption techniques, so I
> apologise if these are trivial questions.
>
> Thanks for any help.
>
> regards,
> Gary

"Zemp Dominik" wrote:

> Hi,
>
> 1) Here's an easy example how you can generate a new key pair and save each
> key in a xml file.
>
>         private static void GenerateKeys(string pubFile, string privateFile)
>         {
>             // Create a new RSA signing key and save it in the container.
>             RSA rsaKey = RSA.Create();
>
>             // Write the public and private key in files.
>             StringToFile(pubFile, rsaKey.ToXmlString(false));
>             StringToFile(privateFile, rsaKey.ToXmlString(true));
>         }
>
>         private static void StringToFile(string outfile, string data)
>         {
>             // Write the data into the file.
>             StreamWriter streamWriter = System.IO.File.CreateText(outfile);
>             streamWriter.Write(data);
>             streamWriter.Close();
>         }
>
> 2) The asymmetric encryption is not suitable for the encryption of large
> data. Use the RSA key pair to encrypt a symmetric encryption key.
>
> Regards,
> Dominik
> -----------------------------
> http://blogs.ecreation.ch
>
>
> "Gary Bond" wrote:
>
> > HI All,
> >
> > Could I ask for some help with RSACryptoServiceProvider class. I am trying
> > to write 3 small apps to demonstrate RSA encryption, and giving out a public
> > key as an xml string. One app makes the xml key strings and saves them as
> > files, and the other 2 apps encrypt and decrypt, using those xml strings.
> >
> > 1) I make the keys like this, using code from MSDN
> >
> >         Dim cp As CspParameters = New CspParameters()
> >         cp.Flags = CspProviderFlags.UseMachineKeyStore
> >         Dim RSA As RSACryptoServiceProvider = New
> > RSACryptoServiceProvider(2048, cp)
> >         Dim PubKey as string = RSA.ToXmlString(False)
> >         Dim PrivateKey as string = RSA.ToXmlString(True)
> >     'subsequently save these strings to file
> >
> > Do I need to initialise the CspParameters and use it in the creation of the
> > RSACryptoServiceProvider? Could I just use the parameterless constructor on
> > the RSACryptoServiceProvider to give me a new instance, and then save the
> > public + private xml keystrings, like this
> >
> >         Dim RSA As RSACryptoServiceProvider = New
> > RSACryptoServiceProvider(2048)
> >
> >
> > If I have to use the CspParameters, since I am saving the xml strings for
> > later use, do I have to set the UseMachineKeyStore? Would this code work if I
> > move the exe's to another machine in either case. The idea of these apps is
> > that I give out the public key string file and the encryptor, someone else
> > encrypts some stuff for me at a remote location, and then I decrypt the file
> > they send me with my private key.
> >
> >
> > 2) When encrypting, if I try to encrypt a large string of 'stuff', I get a
> > cryptographic error "Key not valid for use in specified state". Heres the
> > code from the function:
> >
> >             Dim RSA As New RSACryptoServiceProvider
> >             RSA.FromXmlString(XMLKey)
> >             Return RSA.Encrypt(DataToEncrypt, False)
> >
> >
> > where XMLKey is the public xml key string from point 1) above, previously
> > saved and re-opened on my hard drive.
> >
> > If I encrypt a small amount of data all goes well and I can decrypt later on
> > with
> >
> >     Dim RSA As New RSACryptoServiceProvider()
> >         RSA.FromXmlString(XMLKey)
> >         ClearTxt = RSA.Decrypt(BytesToDecrypt, False)
> >         Return Encoding.ASCII.GetString(ClearTxt)
> >
> > As you can tell I am very inexperienced with encryption techniques, so I
> > apologise if these are trivial questions.
> >
> > Thanks for any help.
> >
> > regards,
> > Gary