Simon Willison’s Weblog

PHP and "OpenID authentication failed: Bad signature". If you’re seeing a “Bad signature” error in your PHP OpenID application it could be down to a miscompiled GMP library.

Posted 15th February 2007 at 10:02 am

Recent articles

GPT-5: Key characteristics, pricing and model card - 7th August 2025
OpenAI's new open weight (Apache 2) models are really good - 5th August 2025
ChatGPT agent's user-agent - 4th August 2025

gmp 1 openid 213 php 181

Monthly briefing

Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments.

Pay me to send you less!

Sponsor & subscribe