Check if an SSL certificate and private key match in two simple commands. The OpenSSL commands below will require you to replace <file> with your file’s name.
For your SSL certificate:1
openssl x509 -noout -modulus -in <file> | md5sum
For your RSA private key:
openssl rsa -noout -modulus -in <file> | md5sum
The output of these commands should be identical. If it isn’t, your keys do not match.
If you’re running a Microsoft CA and you want to be able to accept enrollment requests from clients supporting keygen (Firefox, Safari, Opera, et cetera) you’ve probably found that the /certsrv/ page allows enrollment, but the requests fail when you attempt to issue the certificate. This is because the server is not parsing the subject attributes from the request. To fix this, run the following on your server as administrator on the command line.
certutil -setreg ca\CRLFlags +CRLF_ALLOW_REQUEST_ATTRIBUTE_SUBJECT
You can also set your server to auto-issue on request for certain certificate profiles. To do this add the CA snap-in and get properties of your CA. Under the policy module tab click properties again and click the “Follow the settings..” radio button.
Recently I needed to do some performance testing of an SSL instance on a VM. I considered using JMeter, but decided to use OpenSSL to get a rudimentary picture instead.
To obtain a basic result, we connect to the server and pull the /index.php file. You can specify whatever file you’d like to download, or none at all if you simply want to test connections.1
openssl s_time -www /index.php -new -connect www.trustwave.com:443
Your result will look something like this:
No CIPHER specified Collecting connection statistics for 30 seconds ttttttttttttttttttttttttttttttttttttttttttttttttttttttttt 159 connections in 5.82s; 27.32 connections/user sec, bytes read 62328 159 connections in 31 real seconds, 392 bytes read per connection
If you’d like to get more specific with performance testing you can even use the -ciphers parameter to explicitly choose the negotiated cipher. You can obtain a list of available ciphers with “openssl ciphers”.
OpenSSL provides several tools that allow you to RSA encrypt/sign arbitrary data files. Of course, directly RSA encrypting large volumes of data is impractical because the encrypted/signed data cannot exceed the size of the key material. This is one of the reasons why SSL connections typically handshake and then pass an AES (or RC4, et cetera) key to do symmetric encryption thereafter.1
Generate a private key. You can change the last number to the preferred modulus size. Keys greater than 4096-bit will take a long time to generate.2
openssl genrsa -out private.pem 4096
With the private key we can now encrypt the data.
openssl rsautl -encrypt -inkey private.pem -in publicfile -out privatefile
To decrypt just reverse it.
openssl rsautl -decrypt -inkey private.pem -in privatefile -out publicfile
If you would rather sign the data…
openssl rsautl -sign -inkey private.pem -in filetosign -out signed_data
To verify the signature just use -verify.3
openssl rsautl -verify -inkey private.pem -in signed_data
Continuing the howto nature of this blog (and its peculiar obsession with OpenSSL), here’s a primer on packaging an arbitrary number of certificates into a single PKCS7 container. These files are quite useful for installing multiple certificates on Windows servers. They differ from PKCS12 (PFX) files in that they can’t store private keys. If you need to generate a PKCS12 then head to that article instead.
This example assumes that you have 2 different certificate files, each in PEM (Base64) format. You can add as many -certfile elements as you want to package in the file. Additionally, concatenated certificate chains are supported. 1
openssl crl2pkcs7 -nocrl -certfile cert1.cer -certfile cert2.cer -out outfile.p7b
If you deal with SSL/TLS long enough you will run into situations where you need to examine what certificates are being presented by a server to the client. The best way to examine the raw output is via (what else but) OpenSSL.1
First let’s do a standard webserver connection (-showcerts dumps the PEM encoded certificates themselves for more extensive parsing if you desire. The output below snips them for readability.):
openssl s_client -showcerts -connect www.domain.com:443
CONNECTED(00000003) --snip-- --- Certificate chain 0 s:/C=US/ST=Texas/L=Carrollton/O=Woot Inc/CN=*.woot.com i:/C=US/O=SecureTrust Corporation/CN=SecureTrust CA -----BEGIN CERTIFICATE----- --snip-- -----END CERTIFICATE----- 1 s:/C=US/O=SecureTrust Corporation/CN=SecureTrust 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----- --snip-- -----END CERTIFICATE----- --- Server certificate subject=/C=US/ST=Texas/L=Carrollton/O=Woot Inc/CN=*.woot.com issuer=/C=US/O=SecureTrust Corporation/CN=SecureTrust CA --- No client certificate CA names sent --- SSL handshake has read 2123 bytes and written 300 bytes --- New, TLSv1/SSLv3, Cipher is RC4-MD5 Server public key is 1024 bit --snip--
There’s a lot of data here so I have truncated several sections to increase readability. Points of interest:
But what if you want to connect to something other than a bog standard webserver on port 443? Well, if you need to use starttls that is also available. As of OpenSSL 0.9.8 you can choose from smtp, pop3, imap, and ftp as starttls options.
openssl s_client -showcerts -starttls imap -connect mail.domain.com:139
If you need to check using a specific SSL version (perhaps to verify if that method is available) you can do that as well. -ssl2, -ssl3, -tls1, and -dtls1 are all choices here.2
openssl s_client -showcerts -ssl2 -connect www.domain.com:443
You can also present a client certificate if you are attempting to debug issues with a connection that requires one.3
openssl s_client -showcerts -cert cert.cer -key cert.key -connect www.domain.com:443
And for those who really enjoy playing with SSL handshakes, you can even specify acceptable ciphers.4
openssl s_client -showcerts -cipher DHE-RSA-AES256-SHA -connect www.domain.com:443
The cipher used above should work for almost any Apache server, but will fail on IIS since it doesn’t support 256-bit AES encryption.