Yahoo released the source code for a plugin that will enable end-to-end encryption of email messages, a planned data-security improvement prompted by disclosures of U.S. National Security Agency snooping.The company is asking security experts to look at its code,published on GitHub, and report vulnerabilities, wrote Alex Stamos, Yahoo’s chief information security officer, in a blog post.

  The plugin should be ready by year end, wrote Stamos, who gave a presentation on Sunday at the South by Southwest conference in Austin, Texas.

  Yahoo and Google have been collaborating to make their email systems compatible with end-to-end encryption, a technology based on the public-key cryptography standard OpenPGP. End-to-end encryption is not widely used, as it can be difficult for non-technical users to set up.