Re: OpenNETCF Cryptography questions - using RSA for licensing strategy

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From: Steven Licciardi (Steven_Licciardi_at_nnoossppaammhotmail.com)
Date: 09/16/04 

Date: Thu, 16 Sep 2004 07:24:15 +0100

I've never done any encryption so am interested to know where you get the
private keys. Do people generate their own keys or are they bought. Is
there a licensing issue with using the RSA algorithm or just in purchasing
keys or neither? Also, is their a standard length of key?

Thanks,

Steven

"casey chesnut" <casey@MORE_spam_PLEASEbrains-N-brawn.com> wrote in message
news:OTZxps5mEHA.3352@TK2MSFTNGP15.phx.gbl...
> the public / private keys are stored on the device.
> the CryptoAPI does this ... on the desktop too.
> they are named rSaContainer and rSaContainerImp,
> depending if it is for the devices key pair or being imported
> respectively.
> the code is in RSACryptoServiceProvider.cs
>
> the following code worked for me.
> it creates the private key on the device,
> passes the private key and plainText to a WS.
> the WS loads the private key and encrypts,
> then returns the cipherText and public key.
> device loads public key and decrypts.
>
> /// DEVICE CODE /////////
> //create key pair on device
> RSACryptoServiceProvider rsa = new
> RSACryptoServiceProvider(KeySpec.KEYEXCHANGE, true);
> string privKey = rsa.ToXmlString(true);
> string pubKey = rsa.ToXmlString(false);
>
> string strData = "text for server to encrypt";
> byte [] baData = Format.GetBytes(strData);
>
> //call web service on device to encrypt
> CryptoServ.Crypto cServ = new CryptoServ.Crypto();
> cServ.Url = csUrl;
>
> string outPubKey;
> string retCipher = cServ.AsymRsaDec(strData, privKey, out outPubKey);
> byte [] outCipher = Format.GetB64(retCipher);
>
> //decrypt on device
> RSACryptoServiceProvider rsa2 = new RSACryptoServiceProvider();
> rsa2.FromXmlString(outPubKey);
> byte [] baUnEnc = rsa2.DecryptValue(outCipher);
> Format.SameBytes(baData, baUnEnc);
>
> MessageBox.Show("success");
>
> /// WEB SERVICE CODE ON DESKTOP ///////
> [WebMethod]
> public string AsymRsaDec(string plain, string privKey, out string
> outPubKey)
> {
> byte[] _plain = GetBytes(plain);
> RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
> rsa.FromXmlString(privKey);
> byte[] ciphertext = rsa.Encrypt(_plain, false);
> outPubKey = rsa.ToXmlString(false);
> return GetBase64(ciphertext);
> }
>
> casey
>
> "gcrasher" <gcrasher76@yahoo.com> wrote in message
> news:d06bbb7f.0409151053.5f0c066a@posting.google.com...
>> I've been trying to figure this out for a while and don't understand
>> what's going on.
>>
>> I'm using RSA algorithm to implement a licensing strategy in which the
>> hardware ID is sent to me, encrypted, and sent back to be decrypted on
>> the device, thus verifying that I actually created the data. This
>> requires encrypting on the desktop using my secure private key, and
>> unencrypting on the device using a public key.
>>
>> For the device I'm using the OpenNET.Security.Cryptography classes and
>> System.Security.Cryptography classes on the desktop (for my license
>> creation utility).
>>
>> I'm not understanding how the key containers work on the device using
>> OpenNETCF classes and I'm guessing that is part of my problem. Unless
>> I create the public/private keys on the device, I get a NTE_BAD_KEY
>> error when trying to decrypt on the device. When a new key set is
>> generated on the device (not to be used, just to *reset* the device so
>> I can attempt to provide my own public key), the old public key no
>> longer decrypts the old data it used to decrypt. If I use the keys the
>> device last generated then my code works fine.
>>
>> It seems that when creating the keys on the device, the public key is
>> stored somehow and even though I am specifying my own public key, the
>> OpenNETCF classes somehow are utilizing or checking that container
>> (maybe?). This decryption will need to occur on devices where the keys
>> were not generated. How is it possible for me to provide the public
>> key myself? Anyone have any ideas how I can get this working the way I
>> need to?
>>
>> Thanks!
>>
>>
>> I've included the code being used below:
>>
>> --------------------------------------
>> ---Create key pair using the device---
>> --------------------------------------
>>
>> using OpenNET.Security.Cryptography;
>>
>> RSACryptoServiceProvider rsa = new
>> RSACryptoServiceProvider(OpenNETCF.Security.Cryptography.NativeMethods.KeySpec.KEYEXCHANGE,
>> true);
>>
>> // Save the public key to pubkey.txt
>> FileStream fs = new FileStream("pubkey.txt", FileMode.Create);
>> StreamWriter sw = new StreamWriter(fs);
>> sw.Write(rsa.ToXmlString(false));
>>
>> // Save the private key to privkey.txt
>> fs = new FileStream("privkey.txt", FileMode.Create);
>> sw = new StreamWriter(fs);
>> sw.Write(rsa.ToXmlString(true));
>>
>> ---------------------------------
>> ---Encrypt data on the desktop---
>> ---------------------------------
>>
>> using System.Security.Cryptography;
>>
>> string plain = "Text to be encrypted.";
>> RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
>>
>> // Get the XML string from the privkey.txt file
>> FileStream fs = new FileStream("privkey.txt", FileMode.Open);
>> StreamReader sr = new StreamReader(fs);
>> string privateKeyString = sr.ReadToEnd();
>>
>> // Load private key
>> rsa.FromXmlString(privateKeyString);
>>
>> // convert the plaintext to a byte array using UTF-8
>> UTF8Encoding utf8 = new UTF8Encoding();
>> byte[] plaintext = utf8.GetBytes(plain);
>>
>> // Encrypt the plaintext
>> byte[] ciphertext = rsa.Encrypt(plaintext, false);
>>
>> // Create encrypted output file.
>> FileStream ciphertextfile = new FileStream(outputFile,
>> FileMode.Create);
>> ciphertextfile.Write(ciphertext, 0, ciphertext.Length);
>>
>>
>> -----------------------------------
>> ---Decrypt data using the device---
>> -----------------------------------
>>
>> using OpenNET.Security.Cryptography;
>>
>> string publicKey =
>> <RSAKeyValue><Modulus>qe9vUaTreNvSRynh36T4b74VRqdCOEHhX1xrkdmrwkRBs5yhRBAD+BM2yB5kL7aA
>> BLvW+biQAZCfVDnh3wIMUuzd9pwYaU8FtL8pnq7EEu6ps3a5C7M63fZTj1slFSiTMiGY6rCMOCajSFeOEULMPF
>> Ukj5wJ8WBjWWtRU1HYt/U=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>";
>>
>> RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
>> UTF8Encoding utf8 = new UTF8Encoding();
>>
>> // Read encrypted file.
>> byte[] encryptedBytes = Utility.ReadFile(encryptedFileName);
>>
>> // Set public key.
>> rsa.FromXmlString(publicKey);
>>
>> // Decrypt bytes.
>> string unencryptedString = new
>> String(utf8.GetChars(rsa.DecryptValue(encryptedBytes)));
>
>

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