Certificate authority eMudhra exits TLS business after issuing weak private keys

eMudhra Limited, an India-based certificate authority, said it will withdraw from the global SSL/TLS business after researchers found it had issued eight intermediate certificates with private keys so weak they could be cracked in milliseconds. The company’s chairman cited compliance costs, low revenue (about 1% of total), and competition from free certificate providers as additional reasons for the exit.

The defects originated in a key-generation ceremony held on April 30, 2025, when a flaw in the ceremony script produced a second set of low-entropy keys during a wrap/unwrap operation. Staff mistakenly used the weaker keys—with entropy as low as 4 bits—because their labels were similar to the correct keys. The flawed keys were then used to create certificate signing requests, signed by eMudhra’s root, and sent to fellow CA Sectigo for cross-signing.

Browser vendors blocked the affected intermediate certificates within one to two days of disclosure. eMudhra said it likely would have faced revocation by the CA/Browser Forum, an industry body that sets rules for certificate authorities, absent its voluntary withdrawal.

The weakest key contained just 4 bits of entropy, meaning there were at most 256 possible values instead of the expected ~2^384 for NIST P-384 elliptic-curve keys. Other defective keys had 56, 66, 115, 155, 156, 230, and 237 bits of entropy. Because the initial signing produced incorrect certificate revocation list (CRL) signatures, eMudhra resigned CRLs with the flawed keys, compounding the lifecycle integrity failures.

eMudhra acknowledged human errors at multiple steps and said it is re-verifying every key ceremony conducted to date while investigating potential code and process flaws. The episode underscores how a single flaw in a critical ceremony can undermine the integrity of widely trusted cryptographic infrastructure.