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SIP REG Digest認證算法分析

本文轉載自   查看原文   2021-09-19 13:50   148    freeswitch

一、回顧SIP Register的認證過程

  1. Client(通常是話機)向REG Server(一般是OpenSIPS或Freeswitch)發起REGISTER注冊請求（注：此時發送的請求里，只有一些用戶名、客戶端類型之類的普通信息）
  2. REG Server收到請求后，發現里面沒有Digest等安全相關的摘要信息，直接返回401(未授權)，同時會附加額外的安全信息（比如：realm/nonce/algorithm/qop)
  3. Client收到401拒絕返回后，根據服務端返回的realm/nonce/algorithm/qop信息，結合自己的password，計算出一個最終的response digiest(注：是一個md5值)，重新發起第2次REGISTER，並附帶上response digest等認證相關信息。
  4. REG Server根據Client發過來的Authorization認證信息進行校驗，如果校驗通過，則返回200 OK，認證通過

 

二、認證過程中的SIP信令(報文)

這里介紹二種查看REGISTER過程SIP信令的方法：

2.1 打開FreeSwitch的SIP trace功能 

sofia profile internal siptrace on|off

在FreeSwitch控制台中，輸入上面的命令行（on為打開，off為關閉)，然后用Client（比如：免費開源軟電話MicroSIP)注冊，此時FreeSwitch中會輸出4段SIP報文，分別對應認證過程中的4個階段，類似下面這樣：

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

 

參考上圖，啟動WireShark，指定網卡以及抓包的協議為sip后，本機用Client注冊登錄1次，就能抓到這4個階段的SIP信令（注：上圖的REG Server是OpenSIPS），跟FreeSwith做為REG Server對比，可以發現OpenSIPS第3階段，返回的Authorization里，少了cnounce、 qop、nc這3個值，這一點要注意一下。

 

三、Response Digest的計算過程 

通過觀察SIP報文發現，整個注冊過程中Client始終沒有發送過任何password的明文，相對還是很安全的。Client第2次發起REGISTER時，附帶的Response值是關鍵！REG Server將校驗這個值的正確性，校驗通過才會注冊成功。

整個計算過程，分成三步：

3.1 計算HA1

規則如下：

algorithm 
HA1

MD5(或未指定)

MD5(username:realm:password)

MD5-sess

MD5(MD5(username:realm:password):nonce:cnonce)
    注：MD5計算出來的值為32位小寫，password為密碼，只有Client自己知道。

 例1（FreeSwitch充當REG Server）：

 Client第2次提交的REGISTER請求中，Authorization信息為：

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

則HA1 = MD5("1000:10.32.26.25:1234") = 6a5e40ec8a6cbac75b9914b271516a47 （假設password為1234）

 

例2（OpenSIPS充當REG Server)：

第2階段，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"

則HA1 = MD5("440444:10.2.60.171:440444") = 109cf921db79c57e146cd8d46429312d (假設password與username相同，都為440444)

 

3.2 計算HA2

規則如下：

qop
HA2

auth(或未指定)

MD5(method:digestURI)

auth-int

MD5(method:digestURI:MD5(entityBody))

注：digestURI為SIP信令Authorization節點中的uri值，對於注冊來說，method即為固定值REGISTER

例1（FreeSwitch充當REG Server）：

Client第2次提交的REGISTER請求中，Authorization信息為：

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

則HA2 = MD5("REGISTER:sip:10.32.26.25:5070;transport=tcp") = c0a1637fb943febd38e69c2087d58fe9

 

例2（OpenSIPS充當REG Server)：

第2階段，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"

則HA2 = MD5("REGISTER:sip:10.2.60.171:5060") = 9f5c90dad45f8b57a9de5ad977027d7b

 

3.3 計算Response

根據前2步計算出來的HA1及HA2，計算response值，規則如下：

qop
response
未指定 
MD5(HA1:nonce:HA2)
auth或auth-int 
MD5(HA1:nonce:nonceCount:cnonce:qop:HA2)

計算結果如下：

 
例1(FreeSwitch充當REG Server)
例2(OpenSIPS充當REG Server)
response

MD5("6a5e40ec8a6cbac75b9914b271516a47:bee3366b-cf59-476e-bc5e-334e0d65b386:00000001:c3606b3f70544096a7e17fcdb4670795:auth:c0a1637fb943febd38e69c2087d58fe9")

=7a8049557b2e77602625fa9ee7d8f088

MD5("109cf921db79c57e146cd8d46429312d:6135e48401ea0109021093850f9c5db2bf101786:9f5c90dad45f8b57a9de5ad977027d7b")

=885f45ae2179c9d8ce2bc1cbd8e4bb9f
qop auth 無
nonceCount 00000001 無
nonce bee3366b-cf59-476e-bc5e-334e0d65b386 6135e48401ea0109021093850f9c5db2bf101786
HA2 c0a1637fb943febd38e69c2087d58fe9 9f5c90dad45f8b57a9de5ad977027d7b
HA1 6a5e40ec8a6cbac75b9914b271516a47 109cf921db79c57e146cd8d46429312d
cnonce c3606b3f70544096a7e17fcdb4670795 無

 

附1：話機注銷過程，其中跟注冊過程幾乎完全一樣，只是Expires值會設置為 0，交互報文如下：

 recv 547 bytes from tcp/[10.32.26.25]:61932 at 09:21:34.274829:
   ------------------------------------------------------------------------
   REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0
   Via: SIP/2.0/TCP 10.32.26.25:61932;rport;branch=z9hG4bKPj909d767a192f4db1ad491cb466fe9b99;alias
   Max-Forwards: 70
   From: <sip:1099@10.32.26.25>;tag=c40977782b0d4b87912ff9636fdce333
   To: <sip:1099@10.32.26.25>
   Call-ID: a08b443e427044e8815ed2e3f1dd51d0
   CSeq: 23519 REGISTER
   User-Agent: MicroSIP/3.20.3
   Supported: outbound, path
   Contact: <sip:1099@10.32.26.25:61932;transport=TCP;ob>;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000011058e7e>"
   Expires: 0
   Content-Length:  0

   ------------------------------------------------------------------------
send 670 bytes to tcp/[10.32.26.25]:61932 at 09:21:34.279829:
   ------------------------------------------------------------------------
   SIP/2.0 401 Unauthorized
   Via: SIP/2.0/TCP 10.32.26.25:61932;rport=61932;branch=z9hG4bKPj909d767a192f4db1ad491cb466fe9b99;alias
   From: <sip:1099@10.32.26.25>;tag=c40977782b0d4b87912ff9636fdce333
   To: <sip:1099@10.32.26.25>;tag=6e3DjUDX76p3N
   Call-ID: a08b443e427044e8815ed2e3f1dd51d0
   CSeq: 23519 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="7ff40180-f465-465c-8ca1-44c77d2107f4", algorithm=MD5, qop="auth"
   Content-Length: 0

   ------------------------------------------------------------------------
recv 821 bytes from tcp/[10.32.26.25]:61932 at 09:21:34.279829:
   ------------------------------------------------------------------------
   REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0
   Via: SIP/2.0/TCP 10.32.26.25:61932;rport;branch=z9hG4bKPj793d3c194cd6461589e44c864e031e52;alias
   Max-Forwards: 70
   From: <sip:1099@10.32.26.25>;tag=c40977782b0d4b87912ff9636fdce333
   To: <sip:1099@10.32.26.25>
   Call-ID: a08b443e427044e8815ed2e3f1dd51d0
   CSeq: 23520 REGISTER
   User-Agent: MicroSIP/3.20.3
   Supported: outbound, path
   Contact: <sip:1099@10.32.26.25:61932;transport=TCP;ob>;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000011058e7e>"
   Expires: 0
   Authorization: Digest username="1099", realm="10.32.26.25", nonce="7ff40180-f465-465c-8ca1-44c77d2107f4", uri="sip:10.32.26.25:5070;transport=tcp", response="92e6ae0a0f23e04d21b0866a7746decd", algorithm=MD5, cnonce="85b6265e67b949aa9c2c7bcc26cad2c9", qop=auth, nc=00000001
   Content-Length:  0

   ------------------------------------------------------------------------
send 578 bytes to tcp/[10.32.26.25]:61932 at 09:21:34.286827:
   ------------------------------------------------------------------------
   SIP/2.0 200 OK
   Via: SIP/2.0/TCP 10.32.26.25:61932;rport=61932;branch=z9hG4bKPj793d3c194cd6461589e44c864e031e52;alias
   From: <sip:1099@10.32.26.25>;tag=c40977782b0d4b87912ff9636fdce333
   To: <sip:1099@10.32.26.25>;tag=7Qv6Kpy04FDpH
   Call-ID: a08b443e427044e8815ed2e3f1dd51d0
   CSeq: 23520 REGISTER
   Date: Thu, 23 Sep 2021 09:21:34 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

   ------------------------------------------------------------------------

　　

附2：如果注冊過程中，digest校驗失敗，SIP會返回403，報文如下

recv 647 bytes from tcp/[10.32.26.25]:63125 at 09:26:04.493306:
   ------------------------------------------------------------------------
   REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0
   Via: SIP/2.0/TCP 10.32.26.25:63125;rport;branch=z9hG4bKPj258fc605159e449ea95e1fdd55b4c16d;alias
   Max-Forwards: 70
   From: <sip:1099@10.32.26.25>;tag=69516ebac8224d94a7225271fec56f87
   To: <sip:1099@10.32.26.25>
   Call-ID: 514ac58ec6dd4d8295a62d8f04648c52
   CSeq: 25348 REGISTER
   User-Agent: MicroSIP/3.20.3
   Supported: outbound, path
   Contact: <sip:1099@10.32.26.25:63125;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

   ------------------------------------------------------------------------
send 670 bytes to tcp/[10.32.26.25]:63125 at 09:26:04.496305:
   ------------------------------------------------------------------------
   SIP/2.0 401 Unauthorized
   Via: SIP/2.0/TCP 10.32.26.25:63125;rport=63125;branch=z9hG4bKPj258fc605159e449ea95e1fdd55b4c16d;alias
   From: <sip:1099@10.32.26.25>;tag=69516ebac8224d94a7225271fec56f87
   To: <sip:1099@10.32.26.25>;tag=DemUyr3NK5j6p
   Call-ID: 514ac58ec6dd4d8295a62d8f04648c52
   CSeq: 25348 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="7180f42a-1d76-4a6f-a846-6f9b34f7db4e", algorithm=MD5, qop="auth"
   Content-Length: 0

   ------------------------------------------------------------------------
recv 921 bytes from tcp/[10.32.26.25]:63125 at 09:26:04.496305:
   ------------------------------------------------------------------------
   REGISTER sip:10.32.26.25:5070;transport=tcp SIP/2.0
   Via: SIP/2.0/TCP 10.32.26.25:63125;rport;branch=z9hG4bKPj6727ace0eb4d406cadf969591438a644;alias
   Max-Forwards: 70
   From: <sip:1099@10.32.26.25>;tag=69516ebac8224d94a7225271fec56f87
   To: <sip:1099@10.32.26.25>
   Call-ID: 514ac58ec6dd4d8295a62d8f04648c52
   CSeq: 25349 REGISTER
   User-Agent: MicroSIP/3.20.3
   Supported: outbound, path
   Contact: <sip:1099@10.32.26.25:63125;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="1099", realm="10.32.26.25", nonce="7180f42a-1d76-4a6f-a846-6f9b34f7db4e", uri="sip:10.32.26.25:5070;transport=tcp", response="ba8664d44668c11d030a9436800338e7", algorithm=MD5, cnonce="4c02d90a0bf94ae28a1ecd8cf30b126e", qop=auth, nc=00000001
   Content-Length:  0

   ------------------------------------------------------------------------
send 548 bytes to tcp/[10.32.26.25]:63125 at 09:26:04.499309:
   ------------------------------------------------------------------------
   SIP/2.0 403 Forbidden
   Via: SIP/2.0/TCP 10.32.26.25:63125;rport=63125;branch=z9hG4bKPj6727ace0eb4d406cadf969591438a644;alias
   From: <sip:1099@10.32.26.25>;tag=69516ebac8224d94a7225271fec56f87
   To: <sip:1099@10.32.26.25>;tag=eQDm0KmSge9rj
   Call-ID: 514ac58ec6dd4d8295a62d8f04648c52
   CSeq: 25349 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
   Content-Length: 0

   ------------------------------------------------------------------------

　　

參考文章：

https://en.wikipedia.org/wiki/Digest_access_authentication

https://datatracker.ietf.org/doc/html/rfc2069

https://datatracker.ietf.org/doc/html/rfc2617


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