Connect and share knowledge within a single location that is structured and easy to search. HTTP S is stateless, right? Is it a combination of SSL session cache and cookies? It is usually not directly related to the user session which is determined by the web application and spawns several HTTP requests. Sign up to join this community. The best answers are voted up and rise to the top.
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Viewed 10k times. How long is this symmetric key kept in use by the major browsers before a new key is negotiated? Improve this question.
Add a comment. Active Oldest Votes. So what occurs especially in a Web context is the following: The symmetric keys for a connection remain unchanged until the end of that connection. A connection lives as long as client and server allow it; in a Web context, the server will normally close connections which have gone inactive for more than one or two minutes.
Sessions , i. A typical Web browser will remember SSL sessions until it is closed as a process, i. A typical Web server will remember SSL sessions for some given amount of time, which is configurable typically 10 minutes to 10 hours or so , also subject to available RAM and a configurable limit each remembered session will use a couple of kilobytes at most.
Improve this answer. Community Bot 1. The process of establishing a TLS session is called the handshake negotiation. Before the client and the server can begin exchanging application data over TLS, the encrypted tunnel must be negotiated: the client and the server must agree on the version of the TLS protocol, choose the encryption protocol and verify certificates if necessary.
Unfortunately, each of these steps requires new packet roundtrips between the client and the server, which adds startup latency to all TLS connections. New TLS connections require two roundtrips for a "full handshake". However, in practice, optimized deployments can speed up the process and deliver a consistent one roundtrip TLS handshake.
Such optimized deployment is used when the client has previously communicated with the server. In this case an "abbreviated handshake" can be used, which requires one roundtrip and also allows the client and server to reduce the CPU overhead by reusing the previously negotiated parameters for the secure session.
The extra latency and computational costs of the full TLS handshake impose a serious performance penalty on all applications that require secure communication. To help mitigate some of the costs, TLS Session Resumption provides a mechanism to resume or share the same negotiated secret key data between multiple connections. Session resumption is an important optimization deployment.
The abbreviated handshake eliminates a full roundtrip of latency and significantly reduces computational costs for both sides. In this mechanism , the server assigns a random session ID during the initial handshake with the browser client. Client and server store this session ID along with the session keys and connection states. To resume a session, the client sends the stored session ID with the first protocol message ClientHello to the server.
If the server recognizes the connection and is willing to resume the session, it replies with the same session ID to re-establish the respective session. This allows a secure connection to be established quickly and with no loss of security since we are reusing the previously negotiated session data. However, one of the practical limitations of the Session Identifiers mechanism is the requirement for the server to create and maintain a session cache for every client.
This results in several problems on the server, which may see tens of thousands or even millions of unique connections every day: consumed memory for every open TLS connection, a requirement for a session ID cache and eviction policies, and deployment challenges for popular sites with many servers, which should, ideally, use a shared TLS session cache for best performance.
Hence, for any multi-server deployment, session identifiers will require some careful thinking and systems architecture to ensure a well-operating session cache. To address this concern for server-side deployment of TLS session caches, the "Session Ticket" RFC replacement mechanism was introduced, which removes the requirement for the server to keep the per-client session state.
Instead, if the client indicates that it supports session tickets, the server can include a session ticket record, which includes all of the negotiated session data encrypted with a secret key known only by the server. This session ticket is then stored by the client and can be included in the handshake message of a subsequent session. Thus, all session data is stored only on the client, but the ticket is still safe because it is encrypted with a key known only by the server.
The session ticket mechanism is referred to as the stateless resumption mechanism. The main improvement of stateless resumption is the removal of the server-side session cache, which simplifies deployment by requiring that the client provide the session ticket on every new connection to the server until the ticket has expired.
The draft of TLS 1. After the initial handshake, the server sends a PSK identity to the client. The content of the PSK identity depends on the server and may contain a database lookup key or a self-encrypted and self-authenticated ticket. The client stores this PSK identity along with its own session keys. In a subsequent handshake, the client provides this PSK identity within the ClientHello message to the server.
Depending on the content of the PSK identity, the server decrypts the ticket and uses the contained session keys and connection states to resume the session, or the server uses the contained lookup key to find the session keys and connection states in its own database. Unfortunately, in most cases, security and utility are inversely proportional. Their technique exploits the session resumption feature implemented in the TLS protocol.
A session lasts for a predetermined period of time , from a few minutes up to several hours. If the browser revisits a server within the session window, the ongoing TLS session can resume via a single resumption request, instead of a full handshake negotiation. In this respect, a TLS session resumption is uniquely tied to a specific browser, can be used to track users in the same way cookies might.
Essentially, when a browser resumes a session, the website can correlate the connection with the one that originally created the session, even if the user visits from a different network i. Using the above method, each individual user can be tracked for at most several hours, based on the length of the negotiated session window. The paper calls this technique a prolongation attack. The researchers conclude :. Our results indicate that with the standard-setting of the session resumption lifetime in many current browsers, the average user can be tracked for up to eight days.
Which is why they don't do it. You've just invented yet another obvious vulnerability that would be obviously stupid to implement. You can stop now. They really did think about all this stuff. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How long is an ssl session key valid? And how is it associated with a client? Ask Question. Asked 5 years, 11 months ago. Active 5 years, 11 months ago. Viewed times. I have a few questions on this How long is this session key valid?
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