session - 如何在客户端完全禁用 SSL session 恢复？

Question

我正在使用 OpenSSL 1.0.2g。在我的客户端中，我想完全禁用 SSL session 恢复(出于测试目的)。

我在连接之前、创建 SSL_CTX 之后执行以下操作:

SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_OFF);
SSL_CTX_set_options(ctx, SSL_OP_NO_TICKET);

但是我在流量捕获中看到的是，我的客户端总是通过发送非空 session ID 来进行 session 重用。服务器确实接受了它。

如何完全禁用 SSL session 恢复？

更多扩展代码片段:

SSL_CTX *ctx = NULL;
ctx = SSL_CTX_new(SSLv23_client_method()))
SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_OFF);
SSL_CTX_set_options(ctx, SSL_OP_NO_TICKET);
SSL_CTX_set_verify(ctx, SSL_VERIFY_NONE, NULL);
SSL_CTX_set_verify_depth(ctx, 0);
SSL_CTX_set_mode(ctx, SSL_MODE_AUTO_RETRY);

我做错了什么吗？缺少任何必需的步骤吗？

Answer 1

您正在设置自动重试:

SSL_CTX_set_mode(ctx, SSL_MODE_AUTO_RETRY);

根据 documentation :

SSL_MODE_AUTO_RETRY

Never bother the application with retries if the transport is blocking. If a renegotiation take place during normal operation, a SSL_read or SSL_write would return with -1 and indicate the need to retry with SSL_ERROR_WANT_READ. In a non-blocking environment applications must be prepared to handle incomplete read/write operations. In a blocking environment, applications are not always prepared to deal with read/write operations returning without success report. The flag SSL_MODE_AUTO_RETRY will cause read/write operations to only return after the handshake and successful completion.

这意味着自动重新协商将悄然发生，而使用 OpenSSL 库的应用程序不会意识到。请参阅the documentation for SSL_write() :

If the underlying BIO is blocking, SSL_write() will only return, once the write operation has been finished or an error occurred, except when a renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur. This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the SSL_CTX_set_mode call.

这种“无声”的重新协商可能可以解释您观察到的行为，如果是这样，不使用SSL_MODE_AUTO_RETRY可能会解决您的问题。

OpenSSL 是一个极其复杂的工具，在我看来，许多选项的行为记录很少。对于一个非常相关的示例，“可以使用 SSL_CTX_set_mode 调用的 SSL_MODE_AUTO_RETRY 标志来控制此行为。” 如何控制？ 暗示使用 SSL_MODE_AUTO_RETRY 允许静默重新协商并因此重用 session ，但从未明确说明。

同样，the many options for SSL_CTX_set_session_cache_mode() 之一可能相关:

In order to reuse a session, a client must send the session's id to the server. It can only send exactly one id. The server then either agrees to reuse the session or it starts a full handshake (to create a new session).

A server will lookup up the session in its internal session storage. If the session is not found in internal storage or lookups for the internal storage have been deactivated (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP), the server will try the external storage if available.

所以，确实如此

SSL_SESS_CACHE_OFF

No session caching for client or server takes place.

禁用内部缓存的使用？对我来说，这意味着它不。