India, Oct. 21 -- Eight private keys underpinning part of listed digital trust company eMudhra's certificate infrastructure were so weak that researchers could recover them from publicly available certificates. The discovery prompted Google, Mozilla, Apple, and Microsoft to block the affected certificates, triggering a wider effort to protect browsers, applications, and enterprise systems.

The incident also rattled investors. eMudhra shares hit their 20% lower circuit at Rs.431.55 on the BSE today.

The immediate concern is whether software still trusting the compromised keys could accept fraudulent certificates. A related challenge is replacing legitimate certificates affected by browser makers' decision to withdraw trust in a parent ce...