Eight eMudhra Certificate Authority Keys Were Trivially Guessable, Browsers Respond Within Hours

A certificate authority (CA) is an organisation whose digital certificates tell browsers and software which websites and code to trust. An independent researcher reported on October 17, 2026 that eight intermediate certificates from eMudhra, an Indian digital trust provider, carried private keys that anyone could work out from the public certificate. Six of the certificates issue TLS certificates for websites and two sign code. Chrome and Firefox blocked the intermediates within hours.

Every affected key was a tiny number below 256, giving roughly eight bits of strength instead of the 384 random bits such a key should have. One key was simply the number 4. Testing at most 256 candidates is enough to recover any of them, which a laptop does in milliseconds. That means an attacker could sign certificates that clients trusting eMudhra's G3 hierarchy would accept. The certificates look structurally normal, so only testing the private key against the public key reveals the problem. Sectigo had cross-signed all eight, so each key also appears in a Sectigo-issued certificate.

eMudhra's preliminary explanation points to a flaw in its key-generation ceremony script, which created a second, weak key pair on its hardware security module. Similar key labels led to that weak pair being used for certificate signing requests, and the company cites human errors at several steps. It says it will re-verify every key ceremony it has run, and its investigation was ongoing as of October 21, 2026. Browsers are now protected, but software that relies on its own CA bundle and skips revocation checks may keep trusting the compromised chain.