![]() Please note that ChangeCipherSpec messages don’t belong to this protocol, as they are a protocol by themselves, as seen below.Ĭertificate (server) needed with all key exchange algorithms, except for anonymous ones. The following diagram shows a summary of the process, which has several steps and offers optional ones. ![]() Each set is typically transmitted in a separate TCP segment. The SSL handshake protocol involves four sets of messages (sometimes called flights) that are exchanged between the client and server. Handshake Protocol: It allows the peers to authenticate each other and to negotiate a cipher suite and other parameters of the connection. ![]() Each of these protocols has a very specific purpose, and are used at different stages of the communication: The higher layer is stacked on top of the SSL Record Protocol, and comprises four subprotocols. TLS Record | |ciphertext | Add a TLS Record header | |MAC | Add a Message Authentication Code Compress data (generally no compression applied) The following diagram depicts the process of building an SSL Record.Ģ. One thing to note is that each block is packed into a structure that does not preserve client message boundaries, meaning that multiple messages of the same type may be coalesced into a single structure. In a nutshell, the Record Protocol first fragments the higher-layer protocol data into blocks of 214 bytes or less then optionally compresses the data, adds a Message Authentication Code and finally encrypts the data according to the cipher spec (when negotiated), adding an SSL Record header. This layer consists basically of the TLS Record Protocol. The lower layer is stacked on top of TCP, as it is a connection-oriented and reliable transport layer protocol. This is the general structure of the protocol, and its place in the network stack: Description of the protocolĪs mentioned before, the TLS protocol sits between the Application Layer and the Transport Layer. Nowadays SSL 2.0 and 3.0 as well as their successors TLS 1.0 and TLS 1.1 are considered insecure, so they are being replaced by the newer TLS 1.2 and TLS 1.3 versions. SSL/TLS has evolved considerably since its beginnings. Of course this comes with some drawbacks, as it limits the protocol in some fundamental aspects (such as the inability to use UDP). By acting as such, TLS requires very few changes to the protocols below and above, so the protocol can operate nearly transparently for users, meaning that users need not be aware of the fact that the protocol is in place. SSL/TLS is a separate protocol that inserts itself between the application protocol (generally HTTP, but any other is perfectly possible) and the transport protocol (TCP). It is important to note that SSL/TSL enables applications to be only as secure as the underlying infrastructural components (networks and hosts). In this post I want to show what happens at the protocol level when we use SSL/TLS.
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