什么是SSL上下文？

Question

在为SSL编程时，无论选择哪种语言（C ++，Java，Ruby等），都可能会遇到将要使用的SSLContext对象。我不知道SSLContext在语义上意味着什么？当我搜索谷歌时，只有很多页面解释了这种对象在各种编程语言中的语法用法。

我的问题：SSLContext在SSL方面的意义/做法是什么？无论实现它的语言如何。

Answer 1

SSL Context是密码，协议版本，可信证书，TLS选项，TLS扩展等的集合。由于具有相同设置的多个连接非常常见，因此它们在上下文中放在一起并且相关然后，基于此上下文创建SSL连接。要创建新连接，您只需要参考上下文，这样就可以节省时间和内存，而不必重新创建所有这些设置。

编辑：@EJP很好地将这个“集合”描述为工厂。 SSL上下文与SSL session不同，即使两者都是设置集合。会话是SSL握手后获得的会话，仅涵盖双方同意的密码和协议版本以及交换密钥。鉴于上下文涵盖了所有密码和协议版本以及本地系统（客户端或服务器）在建立新TLS连接时愿意支持的可信证书列表。因此，SSL会话描述了已建立的SSL关系，而SSL上下文描述了建立SSL关系所需的内容。

Answer 2

• SSLContext: Instances of this class represent a secure socket protocol implementation which acts as a factory for secure socket factories or SSLEngines. This class is initialized with an optional set of key and trust managers and source of secure random bytes.

• SSLSession：In SSL, sessions are used to describe an ongoing relationship between two entities. Each SSL connection involves one session at a time, but that session may be used on many connections between those entities, simultaneously or sequentially. The session used on a connection may also be replaced by a different session. Sessions are created, or rejoined, as part of the SSL handshaking protocol. Sessions may be invalidated due to policies affecting security or resource usage, or by an application explicitly calling invalidate. Session management policies are typically used to tune performance.

• SSLSessionContext：A SSLSessionContext represents a set of SSLSessions associated with a single entity. For example, it could be associated with a server or client who participates in many sessions concurrently.。可以使用会话超时配置SSLSessionContext。