How do I fetch a server’s SSL certificate using `openssl`?

The openssl tool has a command s_client which is a general SSL client; i.e. it connects to an SSL-enabled server. HTTPS servers run an SSL on TCP port 443. We can use s_client to connect to them. Here’s an example of connecting to the HTTPS server on google.com and getting the root page. In the course of this, the process prints the “certificate chain” to standard out.

$ openssl s_client -showcerts -connect google.com:443
CONNECTED(00000003)
depth=2 /C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
 0 s:/C=US/ST=California/L=Mountain View/O=Google Inc/CN=*.google.com
   i:/C=US/O=Google Inc/CN=Google Internet Authority G2
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
 1 s:/C=US/O=Google Inc/CN=Google Internet Authority G2
   i:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
-----BEGIN CERTIFICATE-----
MIID8DCCAtigAwIBAgIDAjqSMA0GCSqGSIb3DQEBCwUAMEIxCzAJBgNVBAYTAlVT
MRYwFAYDVQQKEw1HZW9UcnVzdCBJbmMuMRswGQYDVQQDExJHZW9UcnVzdCBHbG9i
YWwgQ0EwHhcNMTUwNDAxMDAwMDAwWhcNMTcxMjMxMjM1OTU5WjBJMQswCQYDVQQG
EwJVUzETMBEGA1UEChMKR29vZ2xlIEluYzElMCMGA1UEAxMcR29vZ2xlIEludGVy
bmV0IEF1dGhvcml0eSBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEB
AJwqBHdc2FCROgajguDYUEi8iT/xGXAaiEZ+4I/F8YnOIe5a/mENtzJEiaB0C1NP
VaTOgmKV7utZX8bhBYASxF6UP7xbSDj0U/ck5vuR6RXEz/RTDfRK/J9U3n2+oGtv
h8DQUB8oMANA2ghzUWx//zo8pzcGjr1LEQTrfSTe5vn8MXH7lNVg8y5Kr0LSy+rE
ahqyzFPdFUuLH8gZYR/Nnag+YyuENWllhMgZxUYi+FOVvuOAShDGKuy6lyARxzmZ
EASg8GF6lSWMTlJ14rbtCMoU/M4iarNOz0YDl5cDfsCx3nuvRTPPuj5xt970JSXC
DTWJnZ37DhF5iR43xa+OcmkCAwEAAaOB5zCB5DAfBgNVHSMEGDAWgBTAephojYn7
qwVkDBF9qn1luMrMTjAdBgNVHQ4EFgQUSt0GFhu89mi1dvWBtrtiGrpagS8wDgYD
VR0PAQH/BAQDAgEGMC4GCCsGAQUFBwEBBCIwIDAeBggrBgEFBQcwAYYSaHR0cDov
L2cuc3ltY2QuY29tMBIGA1UdEwEB/wQIMAYBAf8CAQAwNQYDVR0fBC4wLDAqoCig
JoYkaHR0cDovL2cuc3ltY2IuY29tL2NybHMvZ3RnbG9iYWwuY3JsMBcGA1UdIAQQ
MA4wDAYKKwYBBAHWeQIFATANBgkqhkiG9w0BAQsFAAOCAQEACE4Ep4B/EBZDXgKt
10KA9LCO0q6z6xF9kIQYfeeQFftJf6iZBZG7esnWPDcYCZq2x5IgBzUzCeQoY3IN
tOAynIeYxBt2iWfBUFiwE6oTGhsypb7qEZVMSGNJ6ZldIDfM/ippURaVS6neSYLA
EHD0LPPsvCQk0E6spdleHm2SwaesSDWB+eXknGVpzYekQVA/LlelkVESWA6MCaGs
eqQSpSfzmhCXfVUDBvdmWF9fZOGrXW2lOUh1mEwpWjqN0yvKnFUEv/TmFNWArCbt
F4mmk2xcpMy48GaOZON9muIAs0nH5Aqq3VuDx3CQRk6+0NtZlmwu9RY23nHMAcIS
wSHGFg==
-----END CERTIFICATE-----
 2 s:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
   i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=/C=US/ST=California/L=Mountain View/O=Google Inc/CN=*.google.com
issuer=/C=US/O=Google Inc/CN=Google Internet Authority G2
---
No client certificate CA names sent
---
SSL handshake has read 4106 bytes and written 456 bytes
---
New, TLSv1/SSLv3, Cipher is AES128-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : AES128-SHA
    Session-ID: E30F84973480B9EF70FFD2FF09D5BD10C1B2E73BA58F1FB5C0B350E7CFEB1B95
    Session-ID-ctx:
    Master-Key: C4BF518003989BADE52A8A1BF10CCAAAF55EFC5AA87BB61D4B8783D9C5F8C99018C50C369F41448E5141F67941931BF1
    Key-Arg   : None
    Start Time: 1489443924
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
GET /
HTTP/1.0 302 Found
Cache-Control: private
Content-Type: text/html; charset=UTF-8
Location: https://www.google.es/?gfe_rd=cr&ei=VxzHWLm-Kayp8weTqpeICw
Content-Length: 259
Date: Mon, 13 Mar 2017 22:25:27 GMT
Alt-Svc: quic=":443"; ma=2592000; v="36,35,34"

<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>302 Moved</TITLE></HEAD><BODY>
<H1>302 Moved</H1>
The document has moved
<A HREF="https://www.google.es/?gfe_rd=cr&amp;ei=VxzHWLm-Kayp8weTqpeICw">here</A>.
</BODY></HTML>
read:errno=0

Tagged #openssl, #tls, #certificates, #security, #cli, #programming.

More by Jim

What does the dot do in JavaScript?

foo.bar, foo.bar(), or foo.bar = baz - what do they mean? A deep dive into prototypical inheritance and getters/setters. 2020-11-01

Smear phishing: a new Android vulnerability

Trick Android to display an SMS as coming from any contact. Convincing phishing vuln, but still unpatched. 2020-08-06

A probabilistic pub quiz for nerds

A “true or false” quiz where you respond with your confidence level, and the optimal strategy is to report your true belief. 2020-04-26

Time is running out to catch COVID-19

Simulation shows it’s rational to deliberately infect yourself with COVID-19 early on to get treatment, but after healthcare capacity is exceeded, it’s better to avoid infection. Includes interactive parameters and visualizations. 2020-03-14

The inception bar: a new phishing method

A new phishing technique that displays a fake URL bar in Chrome for mobile. A key innovation is the “scroll jail” that traps the user in a fake browser. 2019-04-27

The hacker hype cycle

I got started with simple web development, but because enamored with increasingly esoteric programming concepts, leading to a “trough of hipster technologies” before returning to more productive work. 2019-03-23

Project C-43: the lost origins of asymmetric crypto

Bob invents asymmetric cryptography by playing loud white noise to obscure Alice’s message, which he can cancel out but an eavesdropper cannot. This idea, published in 1944 by Walter Koenig Jr., is the forgotten origin of asymmetric crypto. 2019-02-16

How Hacker News stays interesting

Hacker News buried my post on conspiracy theories in my family due to overheated discussion, not censorship. Moderation keeps the site focused on interesting technical content. 2019-01-26

My parents are Flat-Earthers

For decades, my parents have been working up to Flat-Earther beliefs. From Egyptology to Jehovah’s Witnesses to theories that human built the Moon billions of years in the future. Surprisingly, it doesn’t affect their successful lives very much. For me, it’s a fun family pastime. 2019-01-20

The dots do matter: how to scam a Gmail user

Gmail’s “dots don’t matter” feature lets scammers create an account on, say, Netflix, with your email address but different dots. Results in convincing phishing emails. 2018-04-07

The sorry state of OpenSSL usability

OpenSSL’s inadequate documentation, confusing key formats, and deprecated interfaces make it difficult to use, despite its importance. 2017-12-02

I hate telephones

I hate telephones. Some rational reasons: lack of authentication, no spam filtering, forced synchronous communication. But also just a visceral fear. 2017-11-08

The Three Ts of Time, Thought and Typing: measuring cost on the web

Businesses often tout “free” services, but the real costs come in terms of time, thought, and typing required from users. Reducing these “Three Ts” is key to improving sign-up flows and increasing conversions. 2017-10-26

Granddad died today

Granddad died. The unspoken practice of death-by-dehydration in the NHS. The Liverpool Care Pathway. Assisted dying in the UK. The importance of planning in end-of-life care. 2017-05-19

How do I call a program in C, setting up standard pipes?

A C function to create a new process, set up its standard input/output/error pipes, and return a struct containing the process ID and pipe file descriptors. 2017-02-17

Your syntax highlighter is wrong

Syntax highlighters make value judgments about code. Most highlighters judge that comments are cruft, and try to hide them. Most diff viewers judge that code deletions are bad. 2014-05-11

Want to build a fantastic product using LLMs? I work at Granola where we're building the future IDE for knowledge work. Come and work with us! Read more or get in touch!

This page copyright James Fisher 2017. Content is not associated with my employer. Found an error? Edit this page.

How do I fetch a server’s SSL certificate using openssl?

Similar posts

More by Jim

How do I fetch a server’s SSL certificate using `openssl`?