一、回顾SIP Register的认证过程
- Client(通常是话机)向REG Server(一般是OpenSIPS或Freeswitch)发起REGISTER注册请求（注：此时发送的请求里，只有一些用户名、客户端类型之类的普通信息）
- REG Server收到请求后，发现里面没有Digest等安全相关的摘要信息，直接返回401(未授权)，同时会附加额外的安全信息（比如：realm/nonce/algorithm/qop)
- Client收到401拒绝返回后，根据服务端返回的realm/nonce/algorithm/qop信息，结合自己的password，计算出一个最终的response digiest(注：是一个md5值)，重新发起第2次REGISTER，并附带上response digest等认证相关信息。
- REG Server根据Client发过来的Authorization认证信息进行校验，如果校验通过，则返回200 OK，认证通过
二、认证过程中的SIP信令(报文)
这里介绍二种查看REGISTER过程SIP信令的方法：
2.1 打开FreeSwitch的SIP trace功能
sofia profile internal siptrace on|off
在FreeSwitch控制台中，输入上面的命令行（on为打开，off为关闭)，然后用Client（比如：免费开源软电话MicroSIP)注册，此时FreeSwitch中会输出4段SIP报文，分别对应认证过程中的4个阶段，类似下面这样：
第1段 REGISTER（Client → FreeSwitch）
recv 647 bytes from tcp/[10.32.26.25]:51696 at 02:14:58.914917: ------------------------------------------------------------------------ REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0 Via: SIP/2.0/TCP 10.32.26.25:51696;rport;branch=z9hG4bKPj8d4db68b24754f539dbf3b563a44fe55;alias Max-Forwards: 70 From: <sip:1000@10.32.26.25>;tag=89aefb1f3fc0413283a453eda5407f60 To: <sip:1000@10.32.26.25> Call-ID: 1e7af0e67a5044658fc7f6716d329642 CSeq: 36850 REGISTER User-Agent: MicroSIP/3.20.3 Supported: outbound, path Contact: <sip:1000@10.32.26.25:51696;transport=TCP;ob>;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000011058e7e>" Expires: 300 Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS Content-Length: 0
第2段 401 Unauthorized(FreeSwitch → Client)
send 670 bytes to tcp/[10.32.26.25]:51696 at 02:14:58.918913: ------------------------------------------------------------------------ SIP/2.0 401 Unauthorized Via: SIP/2.0/TCP 10.32.26.25:51696;rport=51696;branch=z9hG4bKPj8d4db68b24754f539dbf3b563a44fe55;alias From: <sip:1000@10.32.26.25>;tag=89aefb1f3fc0413283a453eda5407f60 To: <sip:1000@10.32.26.25>;tag=Q0m1g96BS3vpa Call-ID: 1e7af0e67a5044658fc7f6716d329642 CSeq: 36850 REGISTER User-Agent: FreeSWITCH-mod_sofia/1.6.18+git~20170612T211449Z~6e79667c0a~64bit Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE Supported: timer, path, replaces WWW-Authenticate: Digest realm="10.32.26.25", nonce="bee3366b-cf59-476e-bc5e-334e0d65b386", algorithm=MD5, qop="auth" Content-Length: 0
第3段 REGISTER (第2次 Client → FreeSwitch)
recv 921 bytes from tcp/[10.32.26.25]:51696 at 02:14:58.925916: ------------------------------------------------------------------------ REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0 Via: SIP/2.0/TCP 10.32.26.25:51696;rport;branch=z9hG4bKPj414de93b6fd34f21a9c453d81117fee2;alias Max-Forwards: 70 From: <sip:1000@10.32.26.25>;tag=89aefb1f3fc0413283a453eda5407f60 To: <sip:1000@10.32.26.25> Call-ID: 1e7af0e67a5044658fc7f6716d329642 CSeq: 36851 REGISTER User-Agent: MicroSIP/3.20.3 Supported: outbound, path Contact: <sip:1000@10.32.26.25:51696;transport=TCP;ob>;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000011058e7e>" Expires: 300 Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS Authorization: Digest username="1000", realm="10.32.26.25", nonce="bee3366b-cf59-476e-bc5e-334e0d65b386", uri="sip:10.32.26.25:5070;transport=tcp", response="7a8049557b2e77602625fa9ee7d8f088", algorithm=MD5, cnonce="c3606b3f70544096a7e17fcdb4670795", qop=auth, nc=00000001 Content-Length: 0
第4段 200 Ok(FreeSwitch → Client)
send 646 bytes to tcp/[10.32.26.25]:51696 at 02:14:58.933914: ------------------------------------------------------------------------ SIP/2.0 200 OK Via: SIP/2.0/TCP 10.32.26.25:51696;rport=51696;branch=z9hG4bKPj414de93b6fd34f21a9c453d81117fee2;alias From: <sip:1000@10.32.26.25>;tag=89aefb1f3fc0413283a453eda5407f60 To: <sip:1000@10.32.26.25>;tag=r9Dtj4QFpcK9N Call-ID: 1e7af0e67a5044658fc7f6716d329642 CSeq: 36851 REGISTER Contact: <sip:1000@10.32.26.25:51696;transport=TCP;ob>;expires=300 Date: Mon, 06 Sep 2021 02:14:58 GMT User-Agent: FreeSWITCH-mod_sofia/1.6.18+git~20170612T211449Z~6e79667c0a~64bit Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE Supported: timer, path, replaces Content-Length: 0
2.2 采用WireShark抓包
参考上图，启动WireShark，指定网卡以及抓包的协议为sip后，本机用Client注册登录1次，就能抓到这4个阶段的SIP信令（注：上图的REG Server是OpenSIPS），跟FreeSwith做为REG Server对比，可以发现OpenSIPS第3阶段，返回的Authorization里，少了cnounce、 qop、nc这3个值，这一点要注意一下。
三、Response Digest的计算过程
通过观察SIP报文发现，整个注册过程中Client始终没有发送过任何password的明文，相对还是很安全的。Client第2次发起REGISTER时，附带的Response值是关键！REG Server将校验这个值的正确性，校验通过才会注册成功。
整个计算过程，分成三步：
3.1 计算HA1
规则如下：
|
algorithm
|
HA1
|
|---|---|
|
MD5(或未指定) |
MD5(username:realm:password) |
|
MD5-sess |
MD5(MD5(username:realm:password):nonce:cnonce) |
- 注：MD5计算出来的值为32位小写，password为密码，只有Client自己知道。
例1（FreeSwitch充当REG Server）：
Client第2次提交的REGISTER请求中，Authorization信息为：
Authorization: Digest username="1000", realm="10.32.26.25", nonce="bee3366b-cf59-476e-bc5e-334e0d65b386", uri="sip:10.32.26.25:5070;transport=tcp", response="7a8049557b2e77602625fa9ee7d8f088", algorithm=MD5, cnonce="c3606b3f70544096a7e17fcdb4670795", qop=auth, nc=00000001
则HA1 = MD5("1000:10.32.26.25:1234") = 6a5e40ec8a6cbac75b9914b271516a47 （假设password为1234）
例2（OpenSIPS充当REG Server)：
第2阶段，FreeSwitch返回的Authorization如下：
Authorization: Digest username="440444", realm="10.2.60.171", nonce="6135e48401ea0109021093850f9c5db2bf101786", uri="sip:10.2.60.171:5060", response="885f45ae2179c9d8ce2bc1cbd8e4bb9f"
则HA1 = MD5("440444:10.2.60.171:440444") = 109cf921db79c57e146cd8d46429312d (假设password与username相同，都为440444)
3.2 计算HA2
规则如下：
|
qop
|
HA2
|
|---|---|
|
auth(或未指定) |
MD5(method:digestURI) |
|
auth-int |
MD5(method:digestURI:MD5(entityBody)) |
注：digestURI为SIP信令Authorization节点中的uri值，对于注册来说，method即为固定值REGISTER
例1（FreeSwitch充当REG Server）：
Client第2次提交的REGISTER请求中，Authorization信息为：
Authorization: Digest username="1000", realm="10.32.26.25", nonce="bee3366b-cf59-476e-bc5e-334e0d65b386", uri="sip:10.32.26.25:5070;transport=tcp", response="7a8049557b2e77602625fa9ee7d8f088", algorithm=MD5, cnonce="c3606b3f70544096a7e17fcdb4670795", qop=auth, nc=00000001
则HA2 = MD5("REGISTER:sip:10.32.26.25:5070;transport=tcp") = c0a1637fb943febd38e69c2087d58fe9
例2（OpenSIPS充当REG Server)：
第2阶段，FreeSwitch返回的Authorization如下：
Authorization: Digest username="440444", realm="10.2.60.171", nonce="6135e48401ea0109021093850f9c5db2bf101786", uri="sip:10.2.60.171:5060", response="885f45ae2179c9d8ce2bc1cbd8e4bb9f"
则HA2 = MD5("REGISTER:sip:10.2.60.171:5060") = 9f5c90dad45f8b57a9de5ad977027d7b
3.3 计算Response
根据前2步计算出来的HA1及HA2，计算response值，规则如下：
|
qop
|
response
|
|---|---|
| 未指定 |
MD5(HA1:nonce:HA2) |
| auth或auth-int |
MD5(HA1:nonce:nonceCount:cnonce:qop:HA2) |
计算结果如下：
|
|
例1(FreeSwitch充当REG Server)
|
例2(OpenSIPS充当REG Server)
|
|---|---|---|
| response |
MD5("6a5e40ec8a6cbac75b9914b271516a47:bee3366b-cf59-476e-bc5e-334e0d65b386:00000001:c3606b3f70544096a7e17fcdb4670795:auth:c0a1637fb943febd38e69c2087d58fe9") =7a8049557b2e77602625fa9ee7d8f088 |
MD5("109cf921db79c57e146cd8d46429312d:6135e48401ea0109021093850f9c5db2bf101786:9f5c90dad45f8b57a9de5ad977027d7b") =885f45ae2179c9d8ce2bc1cbd8e4bb9f |
| qop | auth | 无 |
| nonceCount | 00000001 | 无 |
| nonce | bee3366b-cf59-476e-bc5e-334e0d65b386 | 6135e48401ea0109021093850f9c5db2bf101786 |
| HA2 | c0a1637fb943febd38e69c2087d58fe9 | 9f5c90dad45f8b57a9de5ad977027d7b |
| HA1 | 6a5e40ec8a6cbac75b9914b271516a47 | 109cf921db79c57e146cd8d46429312d |
| cnonce | c3606b3f70544096a7e17fcdb4670795 | 无 |
参考文章：
https://en.wikipedia.org/wiki/Digest_access_authentication
https://datatracker.ietf.org/doc/html/rfc2069