ssl - HelloVerifyRequest 上的 Dtls 握手中使用了错误的 SSL 版本

Question

我在 C 中实现 DTLS 1.2 协议(protocol)。在使用 openSSL 测试客户端时，我观察到 OpenSSL 发送的帧之一没有使用正确的 Dtls 版本 (1.2) 而是旧版本 (1.0)。
C 中的客户端仅支持 DTLS1.2，因此拒绝 OpenSSL 发送的帧。
C客户端发送的HelloClient:

Frame 2461: 109 bytes on wire (872 bits), 109 bytes captured (872 bits) on interface 0
Ethernet II, Src: Infineon_00:00:01 (00:03:19:00:00:01), Dst: Tp-LinkT_dc:4e:82 (50:3e:aa:dc:4e:82)
Internet Protocol Version 4, Src: 192.168.88.73, Dst: 192.168.88.77
User Datagram Protocol, Src Port: 50003, Dst Port: 60003
Datagram Transport Layer Security
    DTLSv1.0 Record Layer: Handshake Protocol: Client Hello
        Content Type: Handshake (22)
        Version: DTLS 1.2 (0xfefd)
        Epoch: 0
        Sequence Number: 0
        Length: 54
        Handshake Protocol: Client Hello

来自 OpenSSL 服务器的响应:

Frame 2464: 90 bytes on wire (720 bits), 90 bytes captured (720 bits) on interface 0
Ethernet II, Src: Tp-LinkT_dc:4e:82 (50:3e:aa:dc:4e:82), Dst: Infineon_00:00:01 (00:03:19:00:00:01)
Internet Protocol Version 4, Src: 192.168.88.77, Dst: 192.168.88.73
User Datagram Protocol, Src Port: 60003, Dst Port: 50003
Datagram Transport Layer Security
    DTLSv1.0 Record Layer: Handshake Protocol: Hello Verify Request
        Content Type: Handshake (22)
        Version: DTLS 1.0 (0xfeff)
        Epoch: 0
        Sequence Number: 0
        Length: 35
        Handshake Protocol: Hello Verify Request

我强制 OpenSSL 使用 1.2 版的 DTLS 运行以下命令:
openssl.exe s_server -nocert -psk 01234567 -accept 443 -cipher PSK-AES128-GCM-SHA256 -dtls1_2
我在 TLS ( https://www.rfc-editor.org/rfc/rfc5246#appendix-E) 的 RFC 中看到

   TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use
   compatible ClientHello messages; thus, supporting all of them is
   relatively easy.  Similarly, servers can easily handle clients trying
   to use future versions of TLS as long as the ClientHello format
   remains compatible, and the client supports the highest protocol
   version available in the server.

没有为 HelloRequestVerify 指定任何内容(rfc5246 或 rfc6347)，但这是否意味着应该接受 1.0 和 1.2 之间的任何版本？
或者这是 OpenSSL 中的一个错误？
注意:如果我继续 DTLS 握手，OpenSSL 发送的每一帧都使用正确版本的 DTLS (1.2)。

Answer 1

根据RFC 6347, 4.2.1. Denial-of-Service Countermeasures

However, in order to avoid the requirement to do version negotiationin the initial handshake, DTLS 1.2 server implementations SHOULD useDTLS version 1.0 regardless of the version of TLS that is expected tobe negotiated.

(该部分包含有关该用法的更多信息。)