Obtaining all certificates in a chain; both intermediate and root

Question

I'm working in Java with Apache's HTTPClient and trying to connect to graph.facebook.com. I'm getting "SSLPeerUnverifiedException: No peer certificate" errors, so I guess Facebook's CA isn't in the default keystore. So I need to create my own keystore with all the certificates that I want to trust, yes? So I found the following command for obtaining the certificate:

echo | openssl s_client -connect graph.facebook.com:443 2>&1 | \
 sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > mycert.pem

Don't know what's going on there, but it seems to have worked. I added the cert to a Bouncy Castle formatted keystore. I created an SSLSocketFactory using the new keystore, but it still doesn't work.

My first guess was, perhaps I don't have all the certificates in the chain (apparently these things come in chains). So how do I know whether there are so-called "intermediate" CAs involved? And how do I grab those certificates? Am I even on the right track?

Answer 1

The SSL Certificate Chain resolver downloads all intermediate certificates for a certificate and concatenates them with the given certificate.

Answer 2

I finally had time to look into this, and it turns out it's super easy! I was only missing ONE option to the openssl command: the showcerts option. Below is an example for obtaining certificates suitable for connecting to Facebook's image server.

Note: I also found out that to authenticate an SSL connection you do NOT want to add the certificate of the endpoint you are connecting to in your keystore. You only want the intermediate and root Certificate Authorities. In some cases, only the root CA or else you will get an exception. See this great blog post for more info.

 $ openssl s_client -connect graph.facebook.com:443 -showcerts
CONNECTED(00000003)
depth=2 /C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
 0 s:/C=US/ST=California/L=Palo Alto/O=Facebook, Inc./CN=*.facebook.com
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance CA-3
-----BEGIN CERTIFICATE-----
MIIFgjCCBGqgAwIBAgIQDKKbZcnESGaLDuEaVk6fQjANBgkqhkiG9w0BAQUFADBm
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
d3cuZGlnaWNlcnQuY29tMSUwIwYDVQQDExxEaWdpQ2VydCBIaWdoIEFzc3VyYW5j
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BhMCVVMxEzARBgNVBAgTCkNhbGlmb3JuaWExEjAQBgNVBAcTCVBhbG8gQWx0bzEX
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a1BHnLLP4mxTHL6faAXYd05IxNn/IA==
-----END CERTIFICATE-----
 1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance CA-3
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
-----BEGIN CERTIFICATE-----
MIIGVTCCBT2gAwIBAgIQCFH5WYFBRcq94CTiEsnCDjANBgkqhkiG9w0BAQUFADBs
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
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9ZKNu8BVIASm2LAXFszj0Mi0PeXZhMbT9m5teMl5Q+h6N/9cNUm/ocU=
-----END CERTIFICATE-----
 2 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
   i:/C=US/O=Entrust.net/OU=www.entrust.net/CPS incorp. by ref. (limits liab.)/OU=(c) 1999 Entrust.net Limited/CN=Entrust.net Secure Server Certification Authority
-----BEGIN CERTIFICATE-----
MIIEQjCCA6ugAwIBAgIEQodApTANBgkqhkiG9w0BAQUFADCBwzELMAkGA1UEBhMC
VVMxFDASBgNVBAoTC0VudHJ1c3QubmV0MTswOQYDVQQLEzJ3d3cuZW50cnVzdC5u
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-----END CERTIFICATE-----
---
Server certificate
subject=/C=US/ST=California/L=Palo Alto/O=Facebook, Inc./CN=*.facebook.com
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance CA-3
---
No client certificate CA names sent
---
SSL handshake has read 4285 bytes and written 309 bytes
---
New, TLSv1/SSLv3, Cipher is RC4-MD5
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : RC4-MD5
    Session-ID: A2AD56513E9EB36D5E4EC193977882BEEC5EC64D07D8E4310C562CC3A4571913
    Session-ID-ctx: 
    Master-Key: 3AC56DD593C864A17D00B08CEFEDB299607491C5E2ABAFE14E2AABADDC8A734B888CC6389BDBE40782EA5ED6E3EAFE4A
    Key-Arg   : None
    Start Time: 1300747299
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---

Answer 3

There are several possibilities to obtain the certificate chain of an SSL connection with HttpClient 4.1

(1) TrustStrategy#isTrusted() can be used to examine chains of certificate presented by the remote server during the ssl handshake while the secure connection is being established.

(2) HttpRoutedConnection#getSSLSession() can be used to obtain a reference to the details of an established SSL session, which among many things should contain a complete certificate chains of the remote server.