I have some data of an X509v3 certificate that is used at a central licensing station. My question is is the following amount of information enough for me to decrypt data using C# code? And additionally, how are the certificate properties imported into a project? Do I have to create a certificate file in order to go on?
Known to me are:
Subject
Serial Number
Issuer
"root-ca"
Public Key Algorithm: "rsaEncryption"
RSA Modulus, 128 bytes
RSA Public Key Exponent
X509v3 Extended Key Usage: "critical"
Signature Algorithm: "md5WithRSAEncryption", followed by 256 untitled bytes
SHA1 Fingerprint
I do not have any certificate file. Excuse me if a similar question has already been answered, unfortunately I wasn't able to find one like mine.
No, your data is not enough. First of all, this is all public data. It doesn't contain a private key. A private key is used for decryption or signature generation. A public key is used for encryption and signature verification.
The .NET API is peculiar in that you can seemingly use a certificate to decrypt. This is not really the case; the certificate and private key pair are seen as one; only if the private key is included then you can actually decrypt. Personally I see this as a minor design mistake.
In principle you could create a certificate given the information. Basically you would have to generate a certificate with the same information and then replace the issuer and signature fields.
This is however not for the weak of heart; I recommend a few years of experience before you even try. If any information is missing from the list above you won't get a valid certificate / signature, and you won't get any warning what is wrong, just a failure. You've got one advantage though; if the signature verifies or fingerprint is identical to the one you've got then you know that you've succeeded.
You would not be able to decrypt of course; the private key would still be missing.
Note that the signature is the 256 untitled bytes.
This information is not enough. This data is a public key to encrypt data.
RSAParameters
Related
I am using a Token based authentication. My web server would generate and encrypt the token. I want the client to decrypt the token to read certain payload information.
What algorithm I should use to achieve this?
In my understanding if I use RSA, I can decrypt in c# using private key whereas the encryption has to happen from other hand so this doesn't fit-in my scenario. Is there any other asymmetric algorithm or ways to achieve this?
Server encrypt - private key.
Client decrypt - public key.
Is there any other asymmetric algorithm or ways to achieve this please suggest.
I want to correct your understanding of asymmetric encryption. Asymmetric encryption allows anyone with the public key to send a secret message to anyone with the private key. Since the public key is public, asymmetric encryption allows many possible senders to send private messages to a few special recipients.
My web server would generate and encrypt the token. I want the client to decrypt the token to read certain payload information.
In that case, with the server sending a secret message to the client, if you are using asymmetric encryption, then the server will encrypt with the public key, and the client will decrypt with the private key.
Server encrypt - private key. Client decrypt - public key.
That is not correct. In asymmetric cryptography, the public key does the encryption and the private key does the decryption.
What you might be thinking about is a digitally signed message. In that case, the sender signs the message with the private key and the receiver verifies the signature with the public key. Digitally signed messages are not secret, though, whereas encrypted messages are secret.
Is there any other asymmetric algorithm or ways to achieve this please suggest.
Since your use case is not entirely clear, I will stop the answer there, and leave it at correcting your understanding of asymmetric encryption. It might be that you need symmetric encryption or a digital signature. I encourage you to ask another, separate StackOverflow question as a follow up to this one.
As a final note, I'll refer you to the Internet Security Glossary. In particular, the section named "$ asymmetric cryptography" has a precise and brief description about how "Asymmetric cryptography can be used to create algorithms for encryption, digital signature, and key agreement."
From your other (unfortunately on hold) question https://stackoverflow.com/questions/49610839/protecting-jwt-signing-and-encryption-c-sharp-solution, it sounds like you require the following:
Send a payload from the server to the client.
Only the client can read the payload, because it is encrypted.
The client can verify who sent the payload, because it is signed.
The recommended approach is to sign-and-then-encrypt. If you are wanting to use asymmetric encryption for both:
use a private to key to sign the payload,
then use a public key to encrypt the signed payload.
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 very specific case for cryptography and I am just not sure what algorithms I need to use to achieve a result I am looking for.
So, it is as follows.
I will distribute an encrypted string to my clients, they will have a password to decrypt it. But I don't want them being able to create such encrypted strings themselves.
So, I need some particular algorithm that would allow me, and only me to encrypt something, and anyone can decrypt it if they have a password. but NOT encrypt.
Can you use certificate based encryption? This is exactly the way HTTPS/SSL encryption works.
The server has a certificate with public and private keys. The private key is used to encrypt data. The certificate with just the public key is distributed to the clients and the public key is used to decrypt data.
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
Is there a way that my server can provide an encrypted string that can be decrypted on the client, but NOT re-encrypted on the client? I know this seems kind of backwards... here's what my need is.
I have a software key that needs to be activated against our remote server. The server needs to provide something back to the client that says "You are active" and contain info such as a date that it's valid until, how many licenses, etc. However, I need to prevent it from being easily tampered with to increase license count or the dates (i.e, re-encrypt the value with a new date using a key found in the de-compiled binary or w/e).
Is such a thing possible using public/private keys? Or perhaps hashes?
EDIT
Alternatively, can the server provide a hash that the client can validate is really from the server without giving the client the ability to spoof or generate a hash on it's own?
Thanks in advance.
Public/private key encryption should do what you need. Hashes are one way functions; a good hash function will make it impossible to retrieve the original value.
In this case, the server has a public/private key pair and the client has a public/private key pair. The server's public key is embedded into the client, and the server has the client's public key as well. The server can now encrypt your payload using it's private key and the client's public key. When the client wants to decrypt the payload, it uses it's private key and the server's public key. The client cannot re-encrypt the data without access to the server's private key.
http://en.wikipedia.org/wiki/Public-key_cryptography - for an explanation of how it all works
http://msdn.microsoft.com/en-us/library/e970bs09.aspx - as a starting point for .Net classes to make it easier
Sure. Use an asymmetric-key algorithm like RSA. Both keys are required to go from cleartext to cleartext; one will encrypt, the other will decrypt. You cannot use the same key you encrypted with to decrypt, and vice-versa. So, the client could not get ciphertext, decrypt it, then use any of the information it has to come up with the same ciphertext.
HOWEVER, asymmetric-key algorithms do not differentiate between the encryption and decryption keys until one is used to encrypt. They only require that the other key is used to decrypt a message encrypted by the first. So, theoretically, your client could "re-encrypt" a message using its "decryption" key that would be decrypt-able by the server using its "encryption key". I don't know of an algorithm that would disallow this; you'd simply have to build it into your communication library by omitting any way to use the decryption key for anything but decrypting.