Posts Tagged: crypto
Check If A Certificate & Private Key Match
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.
- The pipe to md5sum is solely to make the output shorter and easier to visually compare ↩
Firefox Autoenrollment With A Microsoft CA
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.
Using OpenSSL s_time
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”.
- If you would prefer to reuse connections rather than create a new one for each request replace -new with -reuse. ↩
RSA Encryption and Signing
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 |
- Another big reason is speed. AES is much, much faster than RSA. ↩
- If you attempt to encrypt or sign data larger than your key length allows, you will receive an error similar to this: 23465:error:0406D06E:rsa routines:RSA_padding_add_PKCS1_type_2:data too large for key size:rsa_pk1.c:151: ↩
- You can also use -hexdump or -raw to view the data in those forms. ↩
Creating a PKCS7 (P7B) Using OpenSSL
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 wish to provide DER encoded input files (or have DER output) you can use the -inform DER or -outform DER directives. ↩
Checking A Remote Certificate Chain With OpenSSL
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:
- The certificate chain consists of two certificates. At level 0 there is the server certificate with some parsed information. s: is the subject line of the certificate and i: contains information about the issuing CA.
- This particular server (www.woot.com) has sent an intermediate certificate as well. Subject and issuer information is provided for each certificate in the presented chain. Chains can be much longer than 2 certificates in length.
- The server certificate section is a duplicate of level 0 in the chain. If you’re only looking for the end entity certificate then you can rapidly find it by looking for this section.
- No client certificate CAs were sent. If the server was configured to potentially accept client certs the returned data would include a list of “acceptable client CAs”.
- Connection was made via TLSv1/SSLv3 and the chosen cipher was RC4-MD5. Incidentally, this typically means that the server you’re connecting to is IIS.
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.
- The s_client command we’re using opens an interactive socket and does not automatically return to the shell prompt, so remember you will have to hit control-c or type something and hit return to terminate the process. ↩
- This example shows an attempted SSLv2 only connection. SSLv2 should be disabled on any web server you control. It has a variety of flaws and has been superseded by SSLv3/TLSv1 for over a decade. ↩
- This example expects the certificate and private key in PEM form. You can provide them in DER if you add -certform DER and -keyform DER (OpenSSL 0.9.8 or newer only) ↩
- A list of available ciphers can be found by typing “openssl ciphers”, but there are also myriad ways to sort by type and strength. See the ciphers man page for more details. ↩