eMudhra shares fell 20 percent to Rs 432 on October 21, hitting the lower circuit after a flaw left eight of its intermediate certificates with weak keys.

It was the stock's sharpest one-day fall since listing. The shares now trade about 58 percent below their December 2024 peak of Rs 1,024.

A researcher alerted Mozilla on October 17. In theory, the weak keys could let attackers impersonate genuine websites.

Google, Mozilla, Apple and Microsoft moved to block the affected certificates, setting off emergency fixes across browsers and systems.

The weak keys were made during a key-generation ceremony on April 30, 2025, alongside the strong ones, and then published to browser root stores.

eMudhra says its root keys are safe, only one of the eight was in production and none issued end-entity certificates. No fraudulent certificates have been found.

The company says the global website-certificate business is about 1 percent of revenue, and its Indian eSign services work normally.

The IT ministry has set up a special team to investigate, and CERT-In issued an advisory on October 21.

Read the full article for more on the fall in eMudhra shares.