I am using the RSACryptoServiceProvider and C#. I have a web server (A) that will be encrypting data and storing it in a database. I have another server (B) that will be reading the encrypted data and decrypting it. The private key will only ever live on server B.
I would like to limit private key access to my application and a very short list of domain users.
What is the best way to store the key so that it is safe from compromise by an unauthorized person?
You can use Windows RSA Key containers to store the key. The key can be installed / created by the aspnet_regiis.exe tool that ships with the .NET framework.
Here is a walkthrough.
The two options to look out for are:
-pi (installs a key to the RSA container)
-pa (managements permissions for the key)
Related
I had a look on
configSection.SectionInformation.ProtectSection("DataProtectionConfigurationProvider");
but I had two questions:
Is there a way to encrypt config file with a key, because any one can decrypt my file if he knows this method, right?
Does the decryption done automatically when retrieving the connection string at run-time? (in any class, or in data-sets)?
thanks
Yes, Encrypting config file is common. DPAPI way uses symmetric key and therefore, if someone gets the key, he can decrypt.
In my case I used an RSA asymmetric key. That way encryption with public key is performed. Decryption can be performed only with private key protected and held by server in SQL database. On application side, users and application don't need the decrypted secret but need to stay encrypted. Simply, public key is to encrypt and private key is to decrypt. And nobody can easily get the private key.
Furthermore, when it comes to cloud platform like Microsoft Azure, we have to use certificate way which is of also RSA.
My case took almost 1 month to understand the complexity. I completed this task just recently.
The decryption is performed automatically by indicating the thumbprint of private key in the config file.
I have a big XML that needs to be encrypted on one server (by one c# application), and needs to be decrypted on another server (by another c# application). The XML contains the critical information for which this encryption needs to be done.
My real need is that my server that does the encryption should only know the public key and the private key is known only to the server which is doing the decryption. Also, this private key should be stored in a safe area on the server such as certificates.
What should be the steps that can help me achieve so?
Can I generate my private key and store that in certificates or the certificates will generate the private key on their own?
Also, if certificates generate the public and private key, can the public key be separated from the certificate and exported to the server where the encryption has to be done?
How the key-pair and certificate are generated depends on the software used.
The private key can be obtained from a certificate.
The general method is to encrypt data with a symmetric encryption algorithm such as AES and encrypting the symmetric key with asymmetric encryption algorithm such as RSA or EC and the public key. This is done for two reasons: 1. Asymmetric encryption is very slow compared to symmetric encryption. 2. The data length for Asymmetric encryption is limited by the key size: a typical key size is 2048-bits and that limits the data length to 245-bytes.
There is in general no way to securely store a private key (or anything) on the server other than the server being secure short of the server having an HSM or access to a TPM. The main step on making the server secure is 2-factor authentication. But if it is on a shared computer beware of root escalation exploits by other users of the server.
HSM - Hardware Encryption Module
TPM - Trusted Platform Module
Asymmetric encryption is very processor intensive and, consequently very slow. For that reason, it is not normally used to encrypt large amounts of data.
What is normally done is symmetric encryption is used to encrypt the bulk of the data and asymmetric encryption (public key) is used to encrypt the keys used in the symmetric encryption.
The encrypted keys are transmitted with the encrypted data. The keys are decrypted (private key), then using the symmetric keys the bulk data is decrypted.
This is how I have achieved it.
On my server 2, I am generating a certificate(.cer) and a private key(.pvk) using the 'makecert.exe' command. Then, using the 'pvk2pfx.exe', I am generating a .pfx file. This is the file which will now house the certificate and private key.
Now I export the certificate with just the public key to the server 1, where I encrypt the data, and on Server 2 using the certificate's private key I decrypt the data.
For learning purposes, I'm creating a chat application where the connections are done via SSL/TLS, and the messages are encrypted using AES-CBC-256 and the AES keys are encrypted with RSA-2048.
The AES key is randomly generated (AesProvider.GenerateKey()) per user per session (which means one key for every person an user is chatting with) and the IV is randomly generated (AesProvider.GenerateIV()) by passing in the key generated, each time a message is created (before being sent).
On the RSA side, I'm generating a secure random session name to store the private keys generated in containers, and sending out the public key. I'm also using the same model (one key pair per user per session) as in AES.
I should also state that I'm using HMAC-SHA512 to hash the messages and sending the HMAC key encrypted using the same public key that the AES key/Iv gets encrypted with. Since I've read that it doesn't need to be regenerated often, I'm planning on regenerate the HMAC key every 5000 or 10000 calls.
Questions:
1) Should I be creating only one RSA key pair per user and use it for all sessions, or is it good how it is right now?
2) Is using the same AES key and only changing the IV like explained above considered secure?
Not much to answer because what you are doing is the best practice aready.
Some notes though;
RSA key pairs per session is not required (and generating the key is expensve).
You can have only one 2048 bit strong RSA key throughout the lifecycle of your application or for years, since this is what even the most security demanding web applications like e-commerce sites or financial applications do.
You should have a random AES key/IV pair for each session, that is fine.
It is better to have one HMAC key per session (not process wide) since you are sending the key securely (RSA encrypted) and you are also sending the HMAC value securely (AES encrypted) on the wire.
Changing only the IV is almost equal to changing the key and IV (in a sense) because the encrypted output will be different for the same content if you change the IV.
One note however. To prevent a man-in-the-middle attack mimicking your server certificate, is your client code validating the certificate through means of signature checking, or is it just the public key that you are sending without any validation on the client side?
You should have either a self-signed persistent certificate or generate the random certificate (RSA Key Pair) as is issued by the persistent certificate (eg, CN=FrozenDeathChatServer) where the clients during installation of your client software install under the trusted root certificate authorities.
I've been tasked with signing some data with the C# RSACryptoServiceProvider.SignData() Method. In order to generate the public and private key i've used the RSACryptoServiceProvider and passed a keycontainername in order to store the keys safely.
When i run the MSDN example to generate a set of public/private keys on my machine with the fixed keycontainername, the expected public / private keys are generated every time the same.
This will work fine on a single server environment, however, we are operating on an elastic environment where the servers are load balanced. If i encrypt the data with a private key on any one single machine and store this data in through the RSACryptoServiceProvider the data will only exist at the machine level. Each machine will use a different key to sign the data and the user of the public key won't be able to verify the signature.
Is there any way i can store the key safely in a distributed environment?
Thanks
There are two that come to mind.
The first is use X509 certificates that contain the private key. You can use the X509Certificate2 class to get an RSACryptoServiceProvider instance that has the private key. The certificate and private key itself would be kept in the Windows certificate store. You can then limit access to the private key through the certificate store to certain accounts. You would then just install the certificate on each machine / AMI that needs it.
Your other option is to use an Hardware Security Module. AWS has a service called CloudHSM that allows you to use a network HSM inside of a VPC (I don't know how well that will work with Elastic Bean Stalk). The HSM vendor, SafeNet IIRC, allows installing a CSP that points to the HSM. You'd then give the RSACryptoServiceProvider a instance of CspParameters that accepts the container and CSP name.
The HSM solution is the most secure, albeit more complex and expensive.
If RSACryptoServiceProvider cannot Encrypt data larger than it's KeySize, how RsaProtectedConfigurationProvider is implemented in the .Net framework?
I am working on a utility that is going to be used to encrypt/decrypt some sensitive information. My two encryption provider options are DPAPI and RSA, while DPAPI not suited for web farm kind of environment, RSA is fits because of the Export/Import options with a KeyContainer. This is a stand alone application running on a workstation.
As I am aware that Asymmetric algorithms are not designed for large data, I just tried encrypting a string of length over 400K using the code below and it works well.
if (!section.SectionInformation.IsProtected)
{
section.SectionInformation.ProtectSection("RSAProtectedConfigurationProvider");
section.SectionInformation.ForceSave = true;
config.Save(ConfigurationSaveMode.Full);
}
Definitely this implies that more things are happening behind the scenes apart from the export import key options in aspnet_regiis.exe.
My understanding:
we encrypt myapp.exe.config with RsaProtectedConfigurationProvider, provide a key container name myrsakeycontainer, and export the public and private keys to an xml file myrsakeyfile.xml.
If we want myapp.exe.config to be decrypted in another computer, we import they keypair from myrsakeyfile.xml with a container named myrsakeycontainer.
this works well. I can achieve the same thing in my project via RSACryptoServiceProvider. But I can't handle data that larger than the key size that
new RSACryptoServiceProvider(cspParameters)
generated for me.
I want to be able to decrypt huge data (just in case) just the way
RsaProtectedConfigurationProvider does.
Yes I could use a RijndaelManaged (my favorite) for actual
encryption and for the symmetric key transport (export/import) I
could use the RSACryptoServiceProvider. This leaves me in a
situation that If I want to export/import the symmetric key, I should
first encrypt it with the public key or RSA, import it to another
machine, decrypt with the private key of RSA. Which is export the RSA
key pair along with the encrypted symmetric key.
But, when I export RSA key pair used by
RsaProtectedConfigurationProvider via aspnet_regiis.exe, I
believe that it exports only the public/private key pair in an xml
file and no other information (like the symmetric key information).
So, with just the RSA key pair, how does
RsaProtectedConfigurationProvider manage to derypt (huge - over
400K chars in my case) information that was encrypted on another
computer? In cases it uses a symmetric algorithm (perhaps?!) to
encrypt information, how is that symmetric key exported/imported to another
computer for decryption? Is that symmetric key part of the RSA key container exported via aspnet_regiis.exe or is the symmetric key is contrived dynamic based on an algorithm?
I could get away with a Rijndael, whose key is encrypeted with an RSA
key pair and I can export/import both the RSA key pair and the
Rijndael symmetric key to another computer. (which I have done in the past)
I am interested to know what is used inside
RsaProtectedConfigurationProvider.
Any theories? concepts? links? recommendations? please..
Similar Question - What algorithms are used by RSAProtectedConfigurationProvider in web.config encyrption?
The encrypted symmetric key is stored in the XML alongside the encrypted configuration information that the symmetric key has encrypted.
If you use Reflector to look at the code, what it does is load the XML node and use the asymmetric RSA private key to decrypt a symmetric key stored within the XML node itself.
The function that actually does this magic is here:
public virtual SymmetricAlgorithm GetDecryptionKey(EncryptedData encryptedData, string symmetricAlgorithmUri);
Declaring Type: System.Security.Cryptography.Xml.EncryptedXml
Assembly: System.Security, Version=2.0.0.0
See the code around
this.m_document.SelectNodes("//enc:EncryptedKey", nsmgr);
This blog post has a nice writeup about how you pair Asymmetric and Symmetric algorithms in real-world practice: http://pages.infinit.net/ctech/20031101-0151.html