当建立 TLS/LDAP 或 TLS/HTTP 连接时，线路上会发生什么? [英] What happens on the wire when a TLS / LDAP or TLS / HTTP connection is set up?
问题描述
我正在改写我的问题，希望我能得到更好的回答.我在 serverfault here 上问了一个类似的问题，并且认为一个合适且有效的 TLS 服务器是一个期待STARTTLS"的服务器.命令.
STARTTLS 是否可以发布到正确配置的 LDAP 或 HTTP TLS 服务器而无需额外端口?我知道从 SMTP 的角度来看这是正确的，但不确定我可以将这些经验应用到其他协议的范围有多大.
我花时间阅读(但没有完全掌握)
问:在 TLS over LDAP 或 HTTP 会话建立之前，线路上会发生什么?由于这是基于 TCP 的，我可以简单地 telnet 到该端口并发出一些命令来验证它是否正常工作(到目前为止)?
SSL 和 TLS 在使用方式上几乎没有区别.但是，预先建立 SSL/TLS 与使用诸如 STARTTLS 之类的命令之间存在根本区别.有时，TLS"与SSL"相对使用，表示使用STARTTLS模式".但这是不正确的.
前期 TLS/SSL
在这种情况下，客户端先启动 TLS/SSL 连接，因此首先发生 SSL/TLS 握手.一旦安全套接字启动，使用它的应用程序就可以开始为 TLS 之上的协议发送各种命令(例如 HTTP、这种模式下的 LDAP、SMTP).
在这种模式下，SSL/TLS 版本必须在与普通版本不同的端口上运行，例如:HTTPS 在 443 端口上，LDAPS 在 636 端口上，IMAPS 在 993 端口上，而不是 80、389、143 分别.
实现这些应用协议的层几乎不需要知道它们是在 TLS/SSL 之上运行的.有时，它们只是在诸如 sslwrap 之类的工具中进行隧道传输.
STARTTLS 之后的 TLS(或等效的)
TLS 规范允许随时进行握手，包括在同一 TCP 连接上以纯 TCP 交换一些数据之后.
某些协议(包括 LDAP)合并了一个命令来告诉应用程序协议将进行升级.本质上，LDAP 通信的第一部分以纯文本形式发生，然后发送一个 STARTTLS 消息(仍然是纯文本形式)，这表明当前的 TCP 连接将被重用，但接下来的命令将包裹在 TLS/SSL 层中.在这个阶段，TLS/SSL 握手发生并且通信被升级".到 TLS/SSL.只有在此之后，通信才通过 TLS/SSL 得到保护，并且客户端和服务器都知道他们必须从 TLS 层包装/解开它们的命令(通常在 TCP 层和应用层之间添加一个 TLS 库).
在每个协议中如何实现 STARTTLS 的细节因协议而异(因为这必须在某种程度上与使用它的协议兼容).
即使是 HTTP 也有使用这种机制的变体，尽管它几乎不被支持:RFC 2817 升级到TLS 在 HTTP/1.1 中.这与 HTTPS 的工作方式(RFC 2818)完全不同，后者启动 TLS/首先是 SSL.
STARTTLS 方法的优点是你可以在同一个端口上运行安全和普通变体，缺点是后果，特别是潜在的降级攻击或可能的配置错误.
(编辑:正如@GregS 指出的那样，我删除了一个不正确的句子，谢谢.)
(编辑:我还在 ServerFault 上的这个答案.)
I'm rewording my question so hopefully I can get a better response. I asked a similar question on serverfault here, and think that a proper and valid TLS server is one that expects the "STARTTLS" command.
Is it true that STARTTLS can be issued to a properly configured LDAP or HTTP TLS server without needing an extra port? I know that this is true from an SMTP perspective, but aren't sure how broadly I can apply those experiences to other protocols.
I've spent time reading (but not fully grasping)
- The TLS Spec
- Differences between TLS and SSL
- The SSL Spec
Q: What happens on the wire right before the TLS over LDAP or HTTP session is set up? Since this is TCP based can I simply telnet to that port and issue some command to verify it's working (up to that point)?
There are very few differences between SSL and TLS in the way they are used. There is, however, a fundamental difference between up-front establishment of SSL/TLS and the use of a command such as STARTTLS. Sometimes, "TLS" is used in contrast to "SSL", to mean "using a STARTTLS mode" but this is incorrect.
Up-front TLS/SSL
In this case, the client initiates the TLS/SSL connection before anything else, so SSL/TLS handshake happens first. Once the secure socket is up, the application using it can start sending the various commands for the protocol above TLS (e.g. HTTP, LDAP in this mode, SMTP).
In this mode, the SSL/TLS versions have to run on a different port from their plain counterparts, for example: HTTPS on port 443, LDAPS on port 636, IMAPS on port 993, instead of 80, 389, 143 respectively.
The layers implementing these application protocols barely need to know they're running on top of TLS/SSL. Sometimes, they're simply tunneled in tools such as sslwrap.
TLS after STARTTLS (or equivalent)
The TLS specification allows for the handshake to happen at any time, including after having exchanged some data in plain TCP over the same TCP connection.
Some protocols, including LDAP, incorporate a command to tell the application protocol there will be an upgrade. Essentially, the first part of the LDAP communication happens in plain text, then a STARTTLS message is sent (still in plain text), which indicates that the current TCP connection will be reused but that the next commands will be wrapped within a TLS/SSL layer. At this stage, the TLS/SSL handshake happens and the communication is "upgraded" to TLS/SSL. Only after this the communication is secured via TLS/SSL, and both the client and servers know that they have to wrap/unwrap their commands from the TLS layer (typically adding a TLS library between the TCP layer and the application layer).
The details of how STARTTLS is implemented within each protocol vary depending on the protocol (because this has to be compatible with the protocol using it to some extent).
Even HTTP has a variant using this mechanism, although it's mostly never supported: RFC 2817 Upgrading to TLS Within HTTP/1.1. This is completely different from the way HTTPS works (RFC 2818), which initiates TLS/SSL first.
The advantages of the STARTTLS approach is that you can run both secured and plain variants on the same port, the disadvantages are the consequences of that, in particular potential downgrade attacks or possible mistakes in the configuration.
(EDIT: I've removed an incorrect sentence, as @GregS pointed out, thanks.)
(EDIT: I've also put more on SSL vs. TLS in this answer on ServerFault.)
这篇关于当建立 TLS/LDAP 或 TLS/HTTP 连接时，线路上会发生什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
