Computing

A CLI Method to Check SSL Certificate Expiration Date

I know that browser does this automatically, but it might come in handy if you need to check the expiration date of a SSL certificate through CLI. The key is openssl, OpenSSL command line tool.

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$ echo | openssl s_client -connect example.com:443 2> /dev/null | \
openssl x509 -noout -enddate
notAfter=Nov 28 12:00:00 2018 GMT

The command is consisted of two parts:

  • Retrieve SSL certificate from the server
  • Extract the expiration date data

The openssl program is a command line tool for using the various cryptography functions of OpenSSL’s crypto library from the shell. It can be used for[^1]

  • Creation and management of private keys, public keys and parameters
  • Public key cryptographic operations
  • Creation of X.509 certificates, CSRs and CRLs
  • Calculation of Message Digests
  • Encryption and Decryption with Ciphers
  • SSL/TLS Client and Server Tests
  • Handling of S/MIME signed or encrypted mail
  • Time Stamp requests, generation and verification

What we need here is to perform SSL/TLS Client and Server Tests.

s_client is one of the standard commands of openssl command line tool:

This implements a generic SSL/TLS client which can establish a transparent connection to a remote server speaking SSL/TLS. It’s intended for testing purposes only and provides only rudimentary interface functionality but internally uses mostly all functionality of the OpenSSL ssl library.[^1]

Dig deeper into s_client command:

The s_client command implements a generic SSL/TLS client which connects to a remote host using SSL/TLS. It is a very useful diagnostic tool for SSL servers.[^2]

Option -connect host:port:

This specifies the host and optional port to connect to. If not specified then an attempt is made to connect to the local host on port 4433.[^2]

And the format is:

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$ openssl s_client -connect servername:443 > data

If a connection is established, openssl enters interactive mode:

If a connection is established with an SSL server then any data received from the server is displayed and any key presses will be sent to the server. When used interactively (which means neither -quiet nor -ign_eof have been given), the session will be renegotiated if the line begins with an R, and if the line begins with a Q or if end of file is reached, the connection will be closed down.[^2]

To quit, type Q or <ctr>+d (EOF).

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$ openssl s_client -connect example.com:443 > /tmp/example.com
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 High Assurance
Server CA
verify error:num=20:unable to get local issuer certificate
verify return:0
Q
DONE

Dump the session data:

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$ cat /tmp/example.com
CONNECTED(00000003)
---
Certificate chain
0 s:/C=US/ST=California/L=Los Angeles/O=Internet Corporation for Assigned Names and Numbers/OU=Technology/CN=www.example.org
i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA
1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA
i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=US/ST=California/L=Los Angeles/O=Internet Corporation for Assigned Names and Numbers/OU=Technology/CN=www.example.org
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA ---
No client certificate CA names sent
---
SSL handshake has read 3393 bytes and written 421 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES128-GCM-SHA256
Session-ID: C828441A824CE7B0F6A74BBE890AB23727445EAE8521E19F438E679C39E969B1
Session-ID-ctx:
Master-Key: 38BE4F754FBCB5F41650AD91AA5588ACD88B75D7939487052D9FD2790476E7C6D2512A6451A3FC102958488BF173CB54
Key-Arg : None
PSK identity: None
PSK identity hint: None
SRP username: None
TLS session ticket lifetime hint: 300 (seconds)
TLS session ticket:
0000 - 83 70 c4 28 23 ee 9c 9e-87 1b 96 bf 44 76 ee d3 .p.(#.......Dv..
0010 - 45 c9 be ee a5 c5 42 49-c9 08 35 10 ba 79 03 b4 E.....BI..5..y..
0020 - 46 99 9a f2 d3 7b b5 f2-ad 9e 10 5c 7a 61 c3 0e F....{.....\za..
0030 - e0 09 aa 7a 5e 2a 2e bb-42 6a 08 18 16 ae 56 66 ...z^*..Bj....Vf
0040 - 11 0c 96 1a 4a 20 9f 50-6d f7 e2 53 00 75 6f 07 ....J .Pm..S.uo.
0050 - 7f 94 bf 4a 5f e1 f6 3b-d5 b7 6c 11 bc 33 7b 10 ...J_..;..l..3{.
0060 - 78 e3 81 a0 0b 83 25 d6-e6 a5 64 90 59 24 a6 e9 x.....%...d.Y$..
0070 - 9b b6 4b be 9e 42 1b 03-e0 d7 76 e9 32 87 3e 0d ..K..B....v.2.>.
0080 - 3d 09 09 32 18 fd 04 63-93 fe 33 9f 47 50 d4 c1 =..2...c..3.GP..
0090 - e1 a9 21 cc 67 30 ea 03-7f c1 ee 2a 54 02 c8 11 ..!.g0.....*T...
Start Time: 1475971200
Timeout : 300 (sec)
Verify return code: 20 (unable to get local issuer certificate)
---

To avoid the interactive mode, we can pipe an empty string into the command:

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$ echo | openssl s_client -connect example.com:443 > /tmp/example.com 2> /dev/null

Now we have retrieved the SSL certificate from the server. Next, extract the expiration date. This is done by using the standard command x509:

Randomizing an Array with Sort

How to randomize an array? Use the sort command, with the option:

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-R, --random-sort
sort by random hash of keys

For example:

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$ seq 1 10 | sort -R
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$ seq 1 10 | sort --random-sort
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10

Fixing Authorization Failure in AWS CLI by Synchronizing the Clock

Running into an error when executing an AWS command:

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$ aws ec2 describe-instances
An error occurred (AuthFailure) when calling the DescribeInstances operation: AWS
was not able to validate the provided access credentials

From the error message, it appears to be an error with access credentials. But after updating to a new credential, and even updated the AWS package, the error still persisted. After trying out other commands, there was an error message containing “signature not yet current” with timestamps. So, the actual problem was due to inaccurate local clock. Hence, the solution is to sync the local date and time by polling the Network Time Protocol (NTP) server:

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$ sudo ntpdate pool.ntp.org

ntpdate can be run manually as necessary to set the host clock, or it can be run from the host startup script to set the clock at boot time. This is useful in some cases to set the clock initially before starting the NTP daemon ntpd. It is also possible to run ntpdate from a cron script. However, it is important to note that ntpdate with contrived cron scripts is no substitute for the NTP daemon, which uses sophisticated algorithms to maximize accuracy and reliability while minimizing resource use. Finally, since ntpdate does not discipline the host clock frequency as does ntpd, the accuracy using ntpdate is limited.[^1]

From the description, we can learn that we can make things even easier by installing NTP package:

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$ sudo apt-get install -y ntp

Network Time Protocol daemon and utility programs NTP, the Network Time Protocol, is used to keep computer clocks accurate by synchronizing them over the Internet or a local network, or by following an accurate hardware receiver that interprets GPS, DCF-77, NIST or similar time signals.[^2]

Verify the installation and execution:

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$ ps -e | grep ntpd
4964 ? 00:00:00 ntpd

with the environment:

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$ aws --version
aws-cli/1.10.53 Python/2.7.6 Linux/3.13.0-92-generic botocore/1.4.43

[^1]: $ man nptdate
[^2]: $ apt-cache show ntp

HTTP Methods Truth Table

My take on on HTTP methods and resources:

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+-----------------------------------------------------------+
| # | Request-URI | Method | RE | RNE |
+-----------------------------------------------------------+
| 0 | GET /resources | list | 200 | 200 |
| 1 | GET /resources/entity | load/insert | 200 | 404 |
|-----------------------------------------------------------|
| 2 | POST /resources | create | 201 | 409 |
| 3 | POST /resources/entity | N/A | N/A | N/A |
|-----------------------------------------------------------|
| 4 | PUT /resources | (batch) | 200 | 200 |
| 5 | PUT /resources/entity | replace/save | 204 | 201 |
|-----------------------------------------------------------|
| 6 | PATCH /resources | (batch) | 200 | 200 |
| 7 | PATCH /resources/entity | update | 204 | 404 |
|-----------------------------------------------------------|
| 8 | DELETE /resources | (batch) | 200 | 200 |
| 9 | DELETE /resources/entity | remove/delete | 204 | 404 |
+-----------------------------------------------------------+

Notes:

  1. RE: resource exists
  2. RNE: resource not exists
  3. For batch request, whether resource/entity exists or not, the resulting HTTP
    status code is always 200, because the code is used to indicate the status
    of the operation. The actual status code of each entity is enclosed in the
    response array. When there are no matching entities, the response is an empty
    array, therefore, status code 204 is not used.
  4. There are two situation, a new resource is being created, then the Location
    header must indicate the fully qualified resource URI.