Description (CNA)
Generating the ECDSA nonce k samples a random number r and then truncates this randomness with a modular reduction mod n where n is the order of the elliptic curve. Meaning k = r mod n. The division used during the reduction estimates a factor q_e by dividing the upper two digits (a digit having e.g. a size of 8 byte) of r by the upper digit of n and then decrements q_e in a loop until it has the correct size. Observing the number of times q_e is decremented through a control-flow revealing side-channel reveals a bias in the most significant bits of k. Depending on the curve this is either a negligible bias or a significant bias large enough to reconstruct k with lattice reduction methods. For SECP160R1, e.g., we find a bias of 15 bits.
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| wolfSSL / wolfSSL | affected 0 through 5.6.4 |
CWE
CWE-203
References
- https://github.com/wolfSSL/wolfssl/releases/tag/v5.7.2-stable
- https://github.com/wolfSSL/wolfssl/pull/7020
ADP enrichment
No English description supplied.
No references supplied.