Monthly Archive: November 2015

Diffie-Hellman public key

Diffie-Hellman public key issue

If you are developing web applications that use HTTPS, it could happen to you this year (2015) that, all at a sudden, your browser refused to open the pages from your very own web application. And all this because some Diffie-Hellman public key, which appears to be weak. E.g. if you are using Google Chrome browser, most probably you started to see this problem after upgrading Chrome to version 45. The error message:

Server has a weak, ephemeral Diffie-Hellman public key

It actually means – your server’s DHE (Diffie-Hellman ephemeral key agreement) cipher, that allows Internet protocols to agree on a shared key, has less than 1024 bits. It is described in detail at This problem could compromise connection security by the men-in-the-middle attack Logjam.

As of Java applications, and I assume your project uses Java 6 or Java 7, the main problem is that your application server (e.g. Apache Tomcat) is using by default Java Security Socket Extension (JSSE), which has it’s own DHE parameters which are 768-bit. This is considered weak and most recent versions of the browsers will refuse to establish a secure connection with your application server.

Read more about the options to fix this problem