Who Generates The Session Key

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Creating and managing keys is an important part of the cryptographic process. Symmetric algorithms require the creation of a key and an initialization vector (IV). The key must be kept secret from anyone who should not decrypt your data. The IV does not have to be secret, but should be changed for each session. Asymmetric algorithms require the creation of a public key and a private key. The public key can be made public to anyone, while the private key must known only by the party who will decrypt the data encrypted with the public key. This section describes how to generate and manage keys for both symmetric and asymmetric algorithms.

I'm using openssl on Mac OS X 10.9 to generate a self-signed certificate for Windows Server Remote Desktop Services. Using the command below I can generate the certificate, openssl req -x509 -nodes -days 365 -newkey rsa:4096 -keyout myserver.key -out myserver.crt. X509v3 Key Usage: critical Digital Signature X509v3 Extended Key Usage: critical Code Signing. Ensure certificate validity. Each one of these certificate generation techniques have very specific use cases and one certificate request should not be used for all three use cases even though it is technically possible. Openssl x509v3 Extended Key Usage. I know you can specify the purpose for which a certificate public key can be used for by adding a line like this one in the openssl.cfg file. Openssl generate certificate with extended key usage.

  1. After completion of this step, DS28C36ApplicationSlaveSessionKey.exe sets up and executes the DS28C36 Compute and Read Page Authentication command with the challenge generated by applicationmastersessionkey.exe to produce the Session Key according to Figure 9.
  2. The server and client each generate the Master Secret and session keys based on the Pre-Master Secret. The client sends 'Change cipher spec' notification to server to indicate that the client will start using the new session keys for hashing and encrypting messages.

Symmetric Keys

The symmetric encryption classes supplied by the .NET Framework require a key and a new initialization vector (IV) to encrypt and decrypt data. Whenever you create a new instance of one of the managed symmetric cryptographic classes using the parameterless constructor, a new key and IV are automatically created. Anyone that you allow to decrypt your data must possess the same key and IV and use the same algorithm. Generally, a new key and IV should be created for every session, and neither the key nor IV should be stored for use in a later session.

To communicate a symmetric key and IV to a remote party, you would usually encrypt the symmetric key by using asymmetric encryption. Sending the key across an insecure network without encrypting it is unsafe, because anyone who intercepts the key and IV can then decrypt your data. For more information about exchanging data by using encryption, see Creating a Cryptographic Scheme.

The following example shows the creation of a new instance of the TripleDESCryptoServiceProvider class that implements the TripleDES algorithm.

When the previous code is executed, a new key and IV are generated and placed in the Key and IV properties, respectively.

Sometimes you might need to generate multiple keys. In this situation, you can create a new instance of a class that implements a symmetric algorithm and then create a new key and IV by calling the GenerateKey and GenerateIV methods. The following code example illustrates how to create new keys and IVs after a new instance of the symmetric cryptographic class has been made.

The attacker can then try and find the private key value. Once that is found all the data of that particular session and all other sessions protected with the private key can be decrypted. DHE and ECDHE ciphersuites work differently. The key pairs are generated on the fly; i.e. The key pairs are ephemeral (the E in DHE). Does 'This is an asymmetrical key' mean that the session keys generated on the server and client are not the same? Do bullets 6 and 7 mean that on either the client or the server, the inputs to the algorithm that generates a session key are its own private key, and the other one's public key?

When the previous code is executed, a key and IV are generated when the new instance of TripleDESCryptoServiceProvider is made. Another key and IV are created when the GenerateKey and GenerateIV methods are called.

The key pairs are generated on the fly; i.e. The key pairs are ephemeral (the E in DHE). Both client and server establish a session key. The server (or the client and server) then authenticate by performing signature-generation (for authentication). The Session Key button at the top of the representative console; Pressing Ctrl + F4 or Command + F4; Set how long you want this session key to remain valid. The expiration time applies only to the length of time the key can be used to start a session and does not affect the length of the session itself.

Asymmetric Keys

The .NET Framework provides the RSACryptoServiceProvider and DSACryptoServiceProvider classes for asymmetric encryption. These classes create a public/private key pair when you use the parameterless constructor to create a new instance. Asymmetric keys can be either stored for use in multiple sessions or generated for one session only. While the public key can be made generally available, the private key should be closely guarded.

A public/private key pair is generated whenever a new instance of an asymmetric algorithm class is created. After a new instance of the class is created, the key information can be extracted using one of two methods:

  • The ToXmlString method, which returns an XML representation of the key information.

  • The ExportParameters method, which returns an RSAParameters structure that holds the key information.

Both methods accept a Boolean value that indicates whether to return only the public key information or to return both the public-key and the private-key information. An RSACryptoServiceProvider class can be initialized to the value of an RSAParameters structure by using the ImportParameters method.

Asymmetric private keys should never be stored verbatim or in plain text on the local computer. If you need to store a private key, you should use a key container. For more on how to store a private key in a key container, see How to: Store Asymmetric Keys in a Key Container.

The following code example creates a new instance of the RSACryptoServiceProvider class, creating a public/private key pair, and saves the public key information to an RSAParameters structure.

See also

Override session key in ASP.net?

Jan 24, 2011 11:03 PMKendallBLINK

Hi Guys,

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I am on the final stretches of putting together a complete system to get our new ASP.NET MVC code to co-exists with our legacy PHP code. By co-exists I mean that the PHP code and ASP.NET MVC code can both run on the same web site, and can share data. So we can add new code to the site using ASP.NET MVC, but still have the legacy PHP code working until it is replaced. The key to getting all this to work was to build a system to share session state between ASP.NET and PHP. Since both systems store the session data in different formats, the solution we landed on was to isolate key session variables that need to be 'shared' between the two code bases, and put those into a special shared section in our session tables, encoded in a common format. I am using JSON to encode the shared session variables, and now that I have it all working so that the ASP.NET and PHP code can both grok the same JSON formatted data, everything is working. Well, almost!

The problem I have run into is related to the session ID's. In PHP, if we have an existing session ID in the session cookie we tell PHP to go ahead and use that value, using the session_id() function:

http://us3.php.net/manual/en/function.session-id.php

So the PHP code will happily use a session ID that was generated by the ASP.NET code, once we tell it to use that value. Clearly we had to override the session ID cookie on both PHP and ASP.NET to use the same cookie value, but once that is in place, PHP will happily pick up an existing ASP.NET session and start sharing it. The problem is it does not go the other direction; both PHP and ASP.NET use different algorithms to generate the session ID's, and PHP generates one that is 26 characters long and ASP.NET generates one thast is 24 characters long. But they are both unique.

The catch is that ASP.NET appears to be doing validation on the session identifier and can tell when the identifier was NOT generated by ASP.NET, and it won't use it. Rather it will simply generate a new session identifier so we lose all the information that was in the original session.

So right now everything works great if you first land on an ASP.NET page to start the session, but it all falls apart if you first land on a PHP page, or more importantly at the moment if you do a login via the PHP code because that code regenerates the session during login. Then the first ASP.NET page you hit after that will generate a whole new session, so we are back at square one.

So, to solve this problem there are really only a couple of options:

1. Find some way to tell ASP.NET that I *want* it to use the session ID I provide it, much like the session_id() function works in PHP. If I can do that, I can solve this very easily, but I cannot find anything that would indicate it is even possible.

2. Somehow write some PHP code that can generate a session identifier that is compatible with ASP.NET code. To do that, I need to find out what algorithm is used to generate the session identifiers in ASP.NET, so I could port it over to PHP.

Session Keys Electric S

3. A hack solution related to option 2) would be to have a special ASP.NET page that does nothing except generate a new session, and return the valid session identified to the caller. I could then call that with CURL from the PHP code when it needs to generate a brand new session ID, so that the session ID that is used will be accepted by ASP.NET.

4. Completely replace the entire session module in our ASP.NET code with a custom session module. I know it is possible, and most of it is already done with our custom session state provider anyway, but then I still need to find some code to generate a solid session ID anyway!

Any suggestions on how to solve this problem?

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asp.netalgorithmsession identifier