9/3/2023 0 Comments Wireshark encrypted alertThese range from wildly overgeneral (“bad handshake”? What is bad about it?) to the accurate but unhelpful (“EOF in violation of protocol”, no duh). If those tools work with OpenSSL, and you’ve ever seen them fail, you’ve likely seen one of OpenSSL’s cryptic error strings pop up in your face. Lots of us use tools that work with TLS on a regular basis, usually in the form of HTTPS URLs. Today, I’m going to talk about TLS, and Wireshark’s awesome functionality for trying to understand what happens when TLS goes wrong. This may be the first in a series of posts where I demonstrate how I use Wireshark to investigate networks and to track down bugs in misbehaving implementations. Today I’m going to dive into my go-to debugging tool for network problems: Wireshark. This is a real shame, because some of the tools available to programmers working with computer networks are some of the coolest available to any programmer. This means that many of you don’t have a chance to experience some of the tools and debugging experiences that I do on a nearly daily basis. This answer is a detailed introduction to SSL/TLS, which should help in analysing recorded handshakes.Sometimes in my darker moments I forget that not all programmers get to work with computer networks every day, like I do. Some clients will try several versions: they first begin with a high announced version, but they don't like what they see, they may try again with another announced maximum version. You should inspect these field more thoroughly.Īfter a "change cipher spec", subsequent records are encrypted, so Wireshark cannot see their contents only the general type (handshake, alert, application data.) is visible, because it is part of the record header. They do not necessarily match (although they should, at least after the pair of hello messages). Also, note that when a system sends several successive handshake messages (as is common for a server: the ServerHello is usually followed by a Certificate and then a ServerHelloDone), the messages will usually be wrapped within the same record.Īs for versions, there are two of them in SSL: the protocol version negotiated in the ClientHello and ServerHello, and the one used in the record headers. Notably, there cannot be in SSL an "application data" record if a handshake has not been completed, and a complete handshake (abbreviated or not) necessarily contains two "change cipher spec" messages. Your logs are partial you don't show all packets. This doesn't seem to happen every time: Sometimes a new session will use TLS 1.2, sometimes it falls back to TLS 1.0. I don't know what Encrypted alert means (in Wireshark it is displayed as Encrypt alert (21)) - since it is sent by the client I'm assuming it's a Close notify alert.Ī few seconds after the initial session is closed, a new session starts as follows: Client Hello, version-TLS 1.0Įncrypted alert version-TLS 1.0 įrom this, I conclude the version changes, and so the cipher. ![]() I'm tracing the HTTPS traffic with Wireshark, which looks like this: Client Hello, version-TLS 1.2Įncrypted alert version-TLS 1.2 I have an application that uses HTTPS connections, implemented with WinHTTP in the client and Apache Java in the server. I know that initially, a client sends a Client Hello message to the server which includes the TLS version supported by the client. I'm studying the SSL/TLS protocol, more specifically its handshake.
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