Tips to test SSL parameters in command line

During an Istio set-up with all the SSL Stuff, I had some issues with SSL. So I found the following commands to do some tests.

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Check the certificate exposed by an endpoint

With OpenSSL, we can check if an endpoint support a specific version of TLS, and if yes, with which certificate.

Request

Example to test google.com on port 443 with TLS 1.2

openssl s_client -connect google.com:443 -tls1_2

To test with other versions of TLS, you just need to change tls1_2 by tls1_1 or tls1_3.

Answer

Example of an answer where the endpoint support TLS 1.2

CONNECTED(00000003)
depth=2 O = Digital Signature Trust Co., CN = DST Root CA X3
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = Let's Encrypt Authority X3
verify return:1
depth=0 CN = example.com
verify return:1
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Certificate chain
 0 s:/CN=example.com
   i:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
 1 s:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
   i:/O=Digital Signature Trust Co./CN=DST Root CA X3
---
Server certificate
-----BEGIN CERTIFICATE-----
MIIFDjCCA/agAwIBAgISA0nt67i+GAazJs4e+bBSMqB6MA0GCSqGSIb3DQEBCwUA
MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQD
ExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMzAeFw0xNzA1MjMyMTU5MDBaFw0x
NzA4MjEyMTU5MDBaMBcxFTATBgNVBAMTDGluaXNtZWFpbi5pZTCCASIwDQYJKoZI
hvcNAQEBBQADggEPADCCAQoCggEBANLrc8IH2BP51XLhR6L2/IjRuNYcoj6UH58K
NzA4MjEyMTU5MDBaMBcxFTATBgNVBAMTDGluaXNtZWFpbi5pZTCCASI.........
dl0=
-----END CERTIFICATE-----
subject=/CN=example.com
issuer=/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
---
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: ECDH, P-384, 384 bits
---
SSL handshake has read 3019 bytes and written 463 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
    Session-ID: DF39CB241F6580C6E6570E0E9827D7F8615A71A76359DB4F9D1B9D3AD
    Session-ID-ctx:
    Master-Key: 12E8FF788E15AAA2E95BE35C5864784B90ED5A9AE8352AFE98C7DCADB04E
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1502214066
    Timeout   : 7200 (sec)
    Verify return code: 0 (ok)
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closed

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Do curl with a specific version of TLS

Sometimes you need to do some calls with a specific version of TLS. So here, with curl, you can add parameters to define which version of TLS you want to use.

curl --tlsv1.2 --tls-max 1.2

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Retrieve supported ciphers list

If you are not sure about which ciphers are supported by your server, you can use the following command to list them.

Request

openssl ciphers -v

Answer

Example of one line representing a cipher. Normally you should have a couple of lines like this one.

...
ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(256) Mac=AEAD
...

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I hope it will help you!

Please don't hesitate to give me feedback to help me to improve my writing skills.