How to force TLS v1.0 in PHP

PHP 5.6+ Users

This is a new feature as documented on the PHP 5.6 OpenSSL Changes page.

At time of writing this, PHP5.6 is in Beta1 and thus this isn’t overly useful. People of the future – lucky you!

Everyone Else

The title of this post isn’t strictly accurate as this isn’t possible in PHP < 5.6. However, when working around a problem where a supplier’s API server wasn’t correctly negotiating TLSv1.2 down to its supported TLSv1.0, sending a small subset of ciphers seemed to allow negotiation to complete correctly. This was done by setting some SSL options in the stream context.

I created a context passing it the set of permitted ciphers in CIPHERS(1) format. Code below:

  1. [
  2. 'ssl' => [
  3. 'ciphers' => 'DHE-RSA-AES256-SHA:DHE-DSS-AES256-SHA:AES256-SHA:KRB5-DES-CBC3-MD5:KRB5-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:EDH-DSS-DES-CBC3-SHA:DES-CBC3-SHA:DES-CBC3-MD5:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA:AES128-SHA:RC2-CBC-MD5:KRB5-RC4-MD5:KRB5-RC4-SHA:RC4-SHA:RC4-MD5:RC4-MD5:KRB5-DES-CBC-MD5:KRB5-DES-CBC-SHA:EDH-RSA-DES-CBC-SHA:EDH-DSS-DES-CBC-SHA:DES-CBC-SHA:DES-CBC-MD5:EXP-KRB5-RC2-CBC-MD5:EXP-KRB5-DES-CBC-MD5:EXP-KRB5-RC2-CBC-SHA:EXP-KRB5-DES-CBC-SHA:EXP-EDH-RSA-DES-CBC-SHA:EXP-EDH-DSS-DES-CBC-SHA:EXP-DES-CBC-SHA:EXP-RC2-CBC-MD5:EXP-RC2-CBC-MD5:EXP-KRB5-RC4-MD5:EXP-KRB5-RC4-SHA:EXP-RC4-MD5:EXP-RC4-MD5',
  4. ],
  5. ]
  6. );

 

In a lot of cases, you can just use stream_context_set_default to set this info into the default stream context.

Special Note for SOAP Users

PHP’s SOAP client doesn’t seem to use the default stream context. As such, assign a stream context handle to a variable, as demonstrated above and pass this as a parameter to the SOAPClient constructor:

  1. $soap_client = new SOAPClient('http://webservices.site.com/wsdlfile.wsdl', array('stream_context' => $context));

Ciphers

The list of ciphers above came from OpenSSLWikipedia: OpenSSL is a software library to be used in applications that need to secure communications over computer networks against eavesdropping or need to ascertain the identity of the party at the other end...‘s supported cipher list on the server in question. The command openssl ciphers -v will give you all of the supported ciphers and which crypto protocols they apply to. I filtered out TLSv1.2 and passed this list to the stream_context_create in the above example.

The following shell command should give you what you require:

  1. openssl ciphers -v | grep -v 'TLSv1.2' | cut -d ' ' -f 1 | tr "\n" ':'