This produced a lot of output. In the middle of the output was the following:
verify error:num=20:unable to get local issuer certificate
verify return:0
You are missing a root certificate, and it should be specified either with -CAfile or with -CApath.
However, you may encounter a handshake alert after you fix the root certificate issue. I believe its a client certificate issue caused by me not having one (hence you may not experience it). Below, 0x14094410 is the OpenSSL error, and the SSL error (from the TLS protocol) is simply SSL alert number 40. Alert 40 is the handshake alert, and there's no additional information.
First
Determine the root you need:
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195
CONNECTED(00000003)
depth=1 C = US, O = "Entrust, Inc.", OU = www.entrust.net/rpa is incorporated by reference, OU = "(c) 2009 Entrust, Inc.", CN = Entrust Certification Authority - L1C
verify error:num=20:unable to get local issuer certificate
verify return:0
140067272132264:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140067272132264:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:177:
---
Certificate chain
0 s:/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
i:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
1 s:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
i:/O=Entrust.net/OU=www.entrust.net/CPS_2048 incorp. by ref. (limits liab.)/OU=(c) 1999 Entrust.net Limited/CN=Entrust.net Certification Authority (2048)
So you need Entrust.net Certification Authority (2048). You can download it from Entrust Root Certificates. Its named entrust_2048_ca.cer and it appears to be in PEM format.
Second
Now, run openssl s_client again, but this time with -CAfile entrust_2048_ca.cer. Notice it completes with a Verify return code: 0 (ok):
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CAfile entrust_2048_ca.cer
CONNECTED(00000003)
depth=2 O = Entrust.net, OU = www.entrust.net/CPS_2048 incorp. by ref. (limits liab.), OU = (c) 1999 Entrust.net Limited, CN = Entrust.net Certification Authority (2048)
verify return:1
depth=1 C = US, O = "Entrust, Inc.", OU = www.entrust.net/rpa is incorporated by reference, OU = "(c) 2009 Entrust, Inc.", CN = Entrust Certification Authority - L1C
verify return:1
depth=0 C = US, ST = California, L = Cupertino, O = Apple Inc., OU = iTMS Engineering, CN = gateway.sandbox.push.apple.com
verify return:1
140642906502824:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140642906502824:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:177:
---
Certificate chain
0 s:/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
i:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
1 s:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
i:/O=Entrust.net/OU=www.entrust.net/CPS_2048 incorp. by ref. (limits liab.)/OU=(c) 1999 Entrust.net Limited/CN=Entrust.net Certification Authority (2048)
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
issuer=/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
---
No client certificate CA names sent
---
SSL handshake has read 2683 bytes and written 338 bytes
---
New, TLSv1/SSLv3, Cipher is AES256-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1
Cipher : AES256-SHA
Session-ID:
Session-ID-ctx:
Master-Key: A2F375CC440179ADF831179C32A35AF4...
Key-Arg : None
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1398721005
Timeout : 300 (sec)
Verify return code: 0 (ok)
Third
This is kind of the old way of doing things, back when SSLv3 was still popular. That is, the POODLE attack was unknown:
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CAfile entrust_2048_ca.cer
You should probably switch to TLS 1.0 or above and use Server Name Indication (SNI). SNI is a TLS feature not present in SSL. You might need to force TLS 1.2 in 2016; and you can do so with -tls1_2.
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195
-tls1 -servername gateway.sandbox.push.apple.com -CAfile entrust_2048_ca.cer
Below is information from other comments and answers. I'm gathering them up for convenience. You should upvote the comment or answer as appropriate.
Client Certificate
Korbbit provides additional information below. It addresses the statement I made, "alert handshake failure ... I believe its a client certificate issue caused by me not having one". You should provide feedback for Korbbit if its helpful to you:
if you look at the tutorial again you are meant to type...
-cert PushChatCert.pem -key PushChatKey.pem
With Korbbit's feedback, the answer becomes:
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195
-tls1 -servername gateway.sandbox.push.apple.com
-cert PushChatCert.pem -key PushChatKey.pem -CAfile entrust_2048_ca.cer
ca-certificates bundle and -CApath
From Timur Bakeyev, Entrust.net is a well-known Root Certificate Authority, so it's certificate comes in the common CA certificates bundle (ca-certificates in Debian). It is usually installed, among others, into the /etc/ssl/certs directory and, alternatively, can be referred with the -CApath /etc/ssl/certs/ option.
You can use -CApath in place of -CAfile as follows.
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CApath /etc/ssl/certs/
