I recently had to do the same for a Java application and it took me a while to figure it all out, so I decided to write this post to explain the whole process.įirst of all, I assume that your application is making use of Java’s native capabilities for TLS, also known as SunJSSE. For example, web browsers will log this data when a specific environment variable is populated ( SSLKEYLOGFILE). Depending on the application, there are different ways to log this piece of data. Of course, it goes without saying that this should only be done in testing environments and not in production, because if this piece of data gets leaked the whole TLS session can get compromised. The first thing to do is to log the pre-master secret key from the TLS client. Logging & Importing the pre-master secret key One way to workaround this constraint is to dump this secret piece of data - known as the pre-master secret - from the application and import it into Wireshark, which will then be able to decrypt the TLS traffic. Even though this is very useful from a security perspective, the direct consequence is it makes it harder to decrypt the TLS traffic for the purposes explained previously, since it’s not sufficient to provide the server’s private key to Wireshark. This provides a property known as forward secrecy, which means that even if the server’s (static) private key becomes compromised, any past sessions that might have been intercepted will not be compromised. These algorithms generate a different key pair for every connection, instead of using the same one. Among the available algorithms, there is also a specific category of algorithms that perform what’s known as ephemeral key exchange. In this way, observers of the traffic are unable to decrypt this data without the server’s private key. The public key is advertised to the clients, who are then using it to encrypt a piece of data and send it to the server that is then used to generate the symmetric key. Typically, the server has a key pair, consisting of a public and a private key. TLS makes use of a key exchange algorithm in order to secury agree on a symmetric key that will be used to subsequently encrypt the data that will be exchanged. Fortunately, it still provides some ways for us to decrypt that data. For example, it is still capable of capturing some information that is not encrypted, such as the IP or TCP headers, but it is not capable of presenting the actual application data since they are transmitted in an encrypted form. However, when the underlying traffic is encrypted, then the capabilities of the tool become limited. As a result, it can help someone understand deeply the data exchanged between two systems. Apart from being able to capture data transmitted through a network interface, it is able to understand the major protocols and thus provide additional facilities to the user, such as parsing low-level protocol details and presenting them in a more user-friendly way on its user interface or assembling multiple packets into a coherent stream. Wireshark is one of the main tools used for inspection of network traffic. for troubleshooting or better understanding of intricate details of the underlying protocols. However, there are some benign cases where we are in control of one of the two sides of communication and we want to decrypt the encrypted traffic that is exchanged between them, e.g. TLS relies on a set of cryptographic mechanisms that prevent any eavesdropper from being able to see the actual data that are transferred between the two sides. TLS is one of the main protocols used to exchange data securely over an insecure network, such as the Internet.
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