I have seen articles regarding encrypt/decrypt data using Private/Public key. All I want to do is to just encrypt a generated RSA private key already stored in a file. I have been browsing widely to get an idea how it can be done but with no luck.I presume my question is rather an unusual one. Please help!
First, you need a *Key derivation function, to turn your password into a symmetric key which you can use to encrypt your private key. If you solely use the .NET framework, you should use the Rfc2898DeriveBytes class for that. If you are able to use BouncyCastle, then SCrypt would be preferred.
Then you can encrypt your key, prefreably using the AES algorithm.
Some usable code sample can be found in this answer
Related
I'm looking for an advice regarding cryptography.
I'm working on a .Net application which I need to create a license for it, so I plan to create an encrypted license file which my application will use to know if it is licensed or not.
Handling license is as following:
License Generation:
Generate unique symmetric key.
Use symmetric key to encrypt license information.
Use asymmetric public key to encrypt symmetric key.
Write encrypted symmetric key and encrypted license information to file.
License Decryption:
My application will read license file.
Decrypt symmetric key using asymmetric private key which is embedded
xml file inside dll.
Use decrypted symmetric key to decrypt license information.
My questions are:
If the dll which is responsible for decrypting the license has the asymmetric private key as xml embedded resource, is it possible to spy on the dll to get the key and generate a new license?
Is there another technique I can use which is more secure?
As a very general overview, the simplest way is to sign (there's no real need to encrypt anything really) the information with a private key, and verify the signature with the corresponding public key. That's it. The private key is kept safe and no valid new signatures can be generated without it, so if someone changes the signed information the signature becomes invalid. There's no need for extra symmetric encryption on top of it - it's pointless work as far as I'm concerned.
There are plenty of libraries that already do this easily enough, but it's also not that hard to do it manually. https://github.com/dnauck/Portable.Licensing is one I used before.
Edit: also yes, in general it's very easy to decompile .net assemblies, including extracting resources from them.
I'm looking for a secured way to implement a license file for my application, with flags and features. I read about Asymmetric key mechanism in C#, but the RSA purpose is little opposite from what I need.
I want to generate a license file: encrypted cipher. The application would have the key to decrypt the file - but wont have the ability to re-encrypt it. Everywhere I checked, the example shows how party A generates public and private keys and passes the public key to party B so it can use it for encryption. It's probably there between the lines, but I can't see it.
I checked this one: Encrypting and Decrypting
I can find a way to use the code I see to implement it, but I'm not sure it's really secured.
You can still use asymmetric encryption: generate a public-private key pair, encrypt with the private key, and the client (the "application" as you mentioned) can decrypt it with the public key.
Of course, a public key (and the private key too) can be used for both encrypting and decrypting.
But re-encrypting plain text with a public key would generate a completely different cypher than a cypher encrypted using a private key. Decrypting and re-encrypting with the same key would produce a different result, and so it's useless.
What dcastro said above is absolutely correct, and you should give him credit. I just want to add to it, but can't yet comment. If you encrypt the license information with our private key, and distrute your public key with the application, you would be able to decrypt the license information. Without the private key, it wouldn't be possible to re-encrypt a different version of the license that could be decrypted with the public key without using the private key.
Asymetric encryption works like this.
Information encrypted with public key can only be decrypted using the private key.
Information encrypted with the private key can only be decrypted using the public key.
Now for the kicker.. You're probably going to want to encrypt your license with a symmetric algorithm, and encrypt the key needed to decrypt it with the asymmetric algorithm. This way the length of your license data isn't limited by the asymmetric and the symmetric key can be customer specific.
Like I said, give the credit to dcastro.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Simple 2 way encryption for C#
I want to encrypt data in my C# program, but want to be able to decrypt it later. Does anyone know of any library or tool that I can download that will enable me to do that?
Take a look at the System.Security.Cryptography namespace. There's, for example, the TripleDESCryptoServiceProvider.
You can use Microsoft Enterprise Library there is an encryption block in it
If you take a look at the System.Security.Cryptography namespace in the documentation then you'll find classes for most of the common cryptographic systems.
There are two types of algorithm:
Public key (e.g. RSA) - you encrypt with a public key and then decrypt with a private key.
Symmetric key (e.g. AES, DES) - encryption and decryption is performed with the same key.
Which one to choose depends mainly on your situation. Symmetric key algorithms are typically used for encrypting data because they're faster, but that poses the problem of exchanging the key securely. If you can manually configure the endpoints of communication with the same key, then great. If not then you can either use public key to encrypt everything or - as is used in SSL, etc. - add in a handshake phase where the keys are exchanged via public key cryptography.
There is a built in class for Cryptography
System.Security.Cryptography.RSACryptoServiceProvider
Please check this link RSACryptoServiceProvider
I am trying to encrypt/decrypt a string using c#. I've found countless tutorials on how to this ex: this However most of them assume you already have the key. So my question is:
How do I generate the key ?
Thanks in advance.
If you're using the encryption classes in the System.Security.Cryptography namespace, use the Rfc2898DeriveBytes class (#CodeInChaos points out that it supersedes PasswordDeriveBytes) to derive a key from a password.
If a random key is OK, the SymmetricAlgorithm class has a GenerateKey method.
It depends on you handle the keys.
If you automatically generate the key and just exchange the key over some channel with a key-exchange method then you should generate the key with some strong random number generator like RNGCryptoServiceProvider. Actually most Ciphers in .NET generate a random key automatically.
If you want to have some kind of user entered password then I suggest you to use the Rfc2898DeriveBytes class. There is also a Tutorial on the .NET Security blog about Rfc2898DeriveBytes.
Well depending on what key you want you can generate one here
http://randomkeygen.com/ or https://www.grc.com/passwords.htm
But what type of key are you after?
I'm no crypto expert, but as I understand it, 3DES is a symmetric encryption algorithm, which means it doesnt use public/private keys.
Nevertheless, I have been tasked with encrypting data using a public key, (specifically, a .CER file).
If you ignore the whole symmetric/asymmetric thang, I should just be able to use the key data from the public key as the TripleDES key.
However, I'm having difficulty extracting the key bytes from the .CER file.
This is the code as it stands..
TripleDESCryptoServiceProvider cryptoProvider = new TripleDESCryptoServiceProvider();
X509Certificate2 cert = new X509Certificate2(#"c:\temp\whatever.cer");
cryptoProvider.Key = cert.PublicKey.Key.
The simplest method I can find to extract the raw key bytes from the certificate is ToXmlString(bool), and then doing some hacky substringing upon the returned string.
However, this seems so hackish I feel I must be missing a simpler, more obvious way to do it.
Am I missing a simpler way to use a .cer file to provide the key data to the C# 3DES crypto class, or is hacking it out of the certificate xml string really the best way to go about this?
It's not a good idea to use keys generated for asymmetric cryptography for symmetric cryptography. There's nothing preventing you from coming up with a way of using a public key as an encryption key for 3DES, but the end result will be that anyone having access to the public key (and this means everyone!) will be able to decrypt your ciphertext.
cryptoProvider.Key = cert.GetPublicKey()?
Encrypting large amounts of data with asymmetric cryptography is not the way to go. Instead, encrypt the data with a symmetric algorithm and encrypt the symmetric key (and IV) with your public key.
This page from MSDN really helped me get going with .Net symmetric cryptography.
The real problem here is that the public key is, well, public. Meaning freely available, meaning it's providing zero security of encryption.
Heck, anyone on this thread has all the information they need to decrypt everything. So do googlers.
Please try to encourage your users not to use public key data like that. At the very least, get them to give a password or some other slightly-more-secure chunk you can use to generate a consistent key.
One more thing. Certificate keys vary in size. It can probably handle throwing away extra bytes in the key, but you'll probably get an Array Index / Out Of Bounds exception if the key happens to be shorter than the 3DES key needs. I doubt that'll happen, 3DES only needs 56bits, and cert keys are almost always 256bits or larger.
I think what you are missing is converting the bytes from the string containing the key-bytes.
Hope the method FromBase64String will help you:
byte[] keyBytes = Convert.FromBase64String(sourceString);