如何使用 cURL 调试 SSL 握手？

我想用客户端证书对每个目录身份验证进行故障排除。我特别想知道服务器发送哪些可接受的客户端证书。

如何调试 SSL 握手，最好使用 cURL？

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curl probably does have some options for showing more information but for things like this I always use openssl s_client

With the -debug option this gives lots of useful information

Maybe I should add that this also works with non HTTP connections. So if you are doing "https", try the curl commands suggested below. If you aren't or want a second option openssl s_client might be good

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I have used this command to troubleshoot client certificate negotiation:

openssl s_client -connect www.test.com:443 -prexit

The output will probably contain "Acceptable client certificate CA names" and a list of CA certificates from the server, or possibly "No client certificate CA names sent", if the server doesn't always require client certificates.

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curl -iv https://your.domain.io

That will give you cert and header output if you do not wish to use openssl command.

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  1. For TLS handshake troubleshooting please use openssl s_client instead of curl.
  2. -msg does the trick!
  3. -debug helps to see what actually travels over the socket.
  4. -status OCSP stapling should be standard nowadays.
openssl s_client -connect example.com:443 -tls1_2 -status -msg -debug -CAfile <path to trusted root ca pem> -key <path to client private key pem> -cert <path to client cert pem>

Other useful switches -tlsextdebug -prexit -state

https://www.openssl.org/docs/man1.0.2/man1/s_client.html

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Actually openssl command is a better tool than curl for checking and debugging SSL. Here is an example with openssl:

openssl s_client -showcerts -connect stackoverflow.com:443 < /dev/null

and < /dev/null is for adding EOL to the STDIN otherwise it hangs on the Terminal.

But if you liked, you can wrap some useful openssl commands with curl (as I did with curly) and make it more human readable like so:

# check if SSL is valid
>>> curly --ssl valid -d stackoverflow.com
Verify return code: 0 (ok)
issuer=C = US
O = Let's Encrypt
CN = R3
subject=CN = *.stackexchange.com


option: ssl
action: valid
status: OK

# check how many days it will be valid
>>> curly --ssl date -d stackoverflow.com
Verify return code: 0 (ok)
from: Tue Feb  9 16:13:16 UTC 2021
till: Mon May 10 16:13:16 UTC 2021
days total:  89
days passed: 8
days left:   81


option: ssl
action: date
status: OK

# check which names it supports
curly --ssl name -d stackoverflow.com
*.askubuntu.com
*.blogoverflow.com
*.mathoverflow.net
*.meta.stackexchange.com
*.meta.stackoverflow.com
*.serverfault.com
*.sstatic.net
*.stackexchange.com
*.stackoverflow.com
*.stackoverflow.email
*.superuser.com
askubuntu.com
blogoverflow.com
mathoverflow.net
openid.stackauth.com
serverfault.com
sstatic.net
stackapps.com
stackauth.com
stackexchange.com
stackoverflow.blog
stackoverflow.com
stackoverflow.email
stacksnippets.net
superuser.com


option: ssl
action: name
status: OK

# check the CERT of the SSL
>>> curly --ssl cert -d stackoverflow.com
-----BEGIN CERTIFICATE-----
MIIG9DCCBdygAwIBAgISBOh5mcfyJFrMPr3vuAuikAYwMA0GCSqGSIb3DQEBCwUA
MDIxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MQswCQYDVQQD
EwJSMzAeFw0yMTAyMDkxNjEzMTZaFw0yMTA1MTAxNjEzMTZaMB4xHDAaBgNVBAMM
Eyouc3RhY2tleGNoYW5nZS5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEK
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0pCUFwVVH2E=
-----END CERTIFICATE-----


option: ssl
action: cert
status: OK
小开

curl has a --trace (and --trace-ascii) option, which prints basically everything, including all SSL/TSL handshaking. Since --trace supersedes other verbosity options, all you need is

curl --trace /path/to/trace.log https://example.com

You can then read up on ietf to match the messages from the log to the respective messages from the standard - e.g. TLS v1.2, TLS v1.3, curl even prints the corresponding message number from the standard like:

== Info: TLSv1.3 (OUT), TLS handshake, Client hello (1):

Where the (1) is the message number.

--trace-ascii works just as --trace but does not print the binary data.


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