I have many methods like the below which uses X509Certificate2.PrivateKey
public SomeValue DoSomething(X509Certificate2 cert)
{
// do something that needs the cert.PrivateKey
}
They are working well so far with certificates that are stored in the Windows certificate store whose private keys are accessible. Problem now is that I need to support certificates stored in HSM devices and Azure Key Vault HSM where the private keys can't be loaded into memory (and thus the PrivateKey property is null).
I'm looking for a way to avoid changing signatures of my public methods. If the PrivateKey property is virtual, I would be easily make sub classes and return appropriate AsymmetricAlgorithm implementation for each store type (to be clear, for example in Azure Key Vault HSM, the AsymmetricAlgorithm will be an implementation that calls Azure Key Vault to do signing). Btw, the setter of the PrivateKey property doesn't allow me to set my custom AsymmetricAlgorithm.
Another problem is that the PrivateKey property is out of favor now and the GetRSAPrivateKey extension method is recommended.
Is there any trick that I can use to let an X509Certificate2.PrivateKey or the GetRSAPrivateKey extension method returns an AsymmetricAlgorithm of a type that I want?
When using KV, RSA Private Keys don't leave KV, when you get a 'key' back from KV, you really get a key ID, not the key. You will need to export the cert as a PFX file.
In yodlee deveopment environment, I can't see the private key I need to signed the generated jwt, i see the private key in sandbox, but can't see it in development
Someway I have a private key that isn't working (can't remember how i have this private key, as this is a development that i started time ago, and it stop and now i'm getting it again)
In the yodlee sandbox, you are issued your RSA keypair. This is to speed things along for you.
Once you get out of the sandbox environment, you need to generate your own RSA key pair, and upload your public key with Yodlee while keeping your private key secure, confidential, secret, and not in any mobile devices.
Google "How do I generate an RSA keypair" for info on the command line tools and other sources.
Hi Crypto experts out there, are there any best practices around distributing an ecnrypted package to multiple end user systems, specially if the end system are offline ones? in context of assymetric crypto.
is it must to create unique pub/pvt key sets [ per end user system] and encrypt the same package many times uniquely with the pub keys, resulting in a specific package per end user system? how will this scale?
will it be a good practice to sign the original private key[ corresponding to pub keys used to encrypt the package] with senders private keys and then enrypt using end user systems pub keys and share it directly with end user? through trusted communication.
or, encrypt the pvt key with end user systems public key, sign with senders private key and re-encrypt[symmetric] this with the hash of certain string uniquely identifying a end user system? This hash should be programtically reproducible using system unique identifiers later during decryption processes. This way, to retreive the original private key to decrypt the package, it will require both a corresponding pub key[end user clients] as well as end user machine [the hash of string to be generated at runtime on end user system.] and senders public key to manage the authenticity?
Thank you for any feedback!
I am not an expert, but as I understand asymmetric encryption, you can generate a key pair in the distribution center.
The private key stays secret in the distribution center.
To each offline client you provide the public key (as a file).
Each client generates a secure password for symmetric encryption, and encrypts it using the public key.
The encrypted symmetric key is sent to the distribution center.
The distribution center should associate the encrypted symmetric password to the client that sent it.
At the time of encrypting the package for the specific client, the distribution center will decrypt the symmetric password using the private key, and use it to encrypt the package.
Then the package can be sent to the client, who will use it's own password to decrypt the package.
I need to implement encryption between a C# application and a micro controller (pic32mx795). The issue I'm having is generating a public and private key pair I'm using RSACryptoServiceProvider, but I can only get the key attributes and not the complete public key.
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSAParameters RSAKeyInfo = RSA.ExportParameters(false);
I'm unable to supply the micro controller with the key parameters as it only takes the key (as bytes). There is a library that will be able to do this, but it will only be available sometime in November 2012 (SW300055). I am using the SW300052 library to perform encryption on the micro-controller (key size is limited to 256 bits).
I've also tried bouncycastle suggestion in this thread (generating keys and showing them in a text box). It saves the keys in a PEM format. From what I understand the keys are saved in a base64 format. I've specified the key length to be 256 bits but when converting the public key back to bytes, it is 62 bytes.
byte[] encodedDataAsBytes = Convert.FromBase64String (publicKeyString);
I've also looked at Microsoft's Strong Name tool (sn.exe), but the minimum key size it supports is 384 bits.
Is there any way that I can generate a public private key pair and get the public key in plain text/bytes using c# (or with any other tool)? Am I just better off using symmetric key encryption to encrypt a session key?
You can set up a certificate server on a windows box and request them directly. You'll need to install MS certificate services.
You can also use makecert and access the key with c#.
Or you could generate the keypair programmatically.
According to wikipedia (and other sources), asymmetric encryption always works like this:
Party A has a public and private key
Party B encrypts stuff with A's public key
Party A decrypts stuff with their private key
However, I don't want party A to be able to encrypt their own data and only want to them to be able to decrypt it. Using the asymmetric logic this would result in:
Party A has a private key
Party B has a private key (which is party A's public key)
Party B encrypts stuff with their private key
Party A decrypts stuff with their private key
We will be using this for some sort of license generation/checking. Our clients may not generate a license, but the license file must be readable on the client side.
Is this still asymmetric encryption or should I be looking at different methods?
Party A being able to encrypt messages using the public key is absolutely no problem.
Only you could decrypt them (with your private key) and since you have no reason to do so encrypting something with the public key embedded in your application would cause no harm - just a bunch of useless data the user has since he cannot decrypt it.
For the licensing you simply encrypt (or sign - that's enough and then people will be able to read the restrictions etc in the license file but not modidy them) your license file using your private key. The application then decrypts the file using the embedded public key (or validates the signature).
A user extracting the public key and signing a custom license file with it could not use it since it would only work if your private key was embedded in the application (since that's the key necessary to decrypt something encrypted with the public key).
However, he could very well replace your public key with a custom one (where he has the private key, too) and then sign/encrypt his own license file using his private key. That's not a cryptographical issue though - you simply need to add some anti-cracking/modification measures to make it harder to replace the embedded public key. You could do some checksum validations for example.
You have your private key in the safe, and publish your public key. When you create a license you encrypt it with your private key. The client can only decrypt it with your public key.
If you want to restrict your license to a client, ask the client to generate their keypair, and send their public key to you. You then encrypt the license with their public key, then sign it (or encrypt it again) with your private key.
When the client receives the license they will have to
1. verify the signature of (or decrypt) the license you sent them
2. decrypt the verified data using their own private key.
This ensures that 1. only you can send them the license and 2. only they can decrypt it.
What you'd generally do is generate you license on your side, and encrypt it with your private key. Then your client can read it using your public key. This is (very broadly speaking) how certificate schemes (such as used in secure online browsing with HTTPS) work. And yes, that still absolutely counts as asymmetric encryption.
Based on what you're saying, asymmetric encryption is still what you want, it just needs to be done in a different way than you're used to thinking about it.
Let's say you generate a key pair for A. You send A one half of the pair: it doesn't really matter but we'll call it the private half. You encrypt using the public half and send it on to A. Then A can decrypt it. But A won't be able to encrypt a message that appears to come from the A public key since they only have the private half of the key and you can't figure out the other half of the key if you only have half of it, no matter which half you have. So A could only encrypt messages that could be decrypted by the public key that you have kept as a secret.
Of course, as other posters have already said, there are better ways to set up this protocol. Just trying to explain why this is not really an issue once you understand the details of asymmetric encryption and look past what we like to call the key halves and how we usually use them.
You could have a look at Rhino licensing : http://hibernatingrhinos.com/open-source/rhino-licensing/introduction
The other answers already said how to do it ... here just a note that (at least with RSA) the scheme you described in your question is not secure, if it depends on B's key staying secret.
For RSA, the public and private keys are really asymmetric, and you can't simply swap them and expect the same security properties.
If your party B (Bob) encrypts multiple messages with the same public key, an attacker which reads these (ciphertext) messages can with little effort get your public key. The attacker does not get the plaintexts or the private key, but the public key will always become really "public".
For A (Alice), it is even possible to create the public key from the private one, without any message being encrypted with the public one.
I suppose similar caveats are there for other asymmetric cryptosystems - always use them only like they are specified, and proven.
In this case, you would combine two key pairs: B's one to sign/verify the message (to make sure the message was sent by B), and A's one to encrypt/decrypt the message (to make sure only A can read it).
Yes. You can do it with RSA - to do a Diffie-Hellman-like exchange, because not only do the keys from 1 associated pair commute, but keys from different keypairs can commute as well.
alice -> bob: alice.pub
bob -> alice: bob.pub
alice: r = random.secret()
alice -> bob: ( r * (alice.priv * bob.pub) )
bob: r = ( (r * (alice.priv * bob.pub)) * (bob.priv * alice.pub) )
Notice that we did something odd here. We mixed RSA operations from different keypairs in one operation. The objects in parenthesis are effectively a new virtual RSA key, and neither one of these keys is public. Had we tried to create that RSA key directly, either alice or bob would know both keys of the pair. This keypair is effectively a secret key where you write to one end and only the other side can decrypt it, yet you cant decrypt what you wrote yourself, and nobody else can encrypt messages to the other side.
I have never seen anyone mix keypairs like this, but I tested this by writing the code. I had to do something unusual though because normally, applying the private key to the message is for 'signing'. But signing usually hashes the secret and applies the private key to a hash of it; something we do not want. So in my code, once I had the RSA components (D,E,N) extracted into arbitrary precision numbers... ie: decrypt,encrypt,modulus ... I just did:
wormholeSend(me,you,msg) =
(((me ^ {me_D}) \% me_N) ^ {you_E}) \% you_N
The thing that makes it a little tricky is that E (encrypt exponent) is actually a predictable value, but the modulus N is in the public key (E,N). D is private to each party. We need to be careful here, because you and I have a different modulus N.
I did this because I wanted a system where a program is authorized to encrypt keys that can be decrypted by users. Doing this, the user cannot encrypt keys, and the program cannot decrypt them.