CVE-2024-1544
Severity:
MEDIUM
Type:
Unavailable / Other
Publication date:
27/08/2024
Last modified:
28/08/2024
Description
Generating the ECDSA nonce k samples a random number r and then <br />
truncates this randomness with a modular reduction mod n where n is the <br />
order of the elliptic curve. Meaning k = r mod n. The division used <br />
during the reduction estimates a factor q_e by dividing the upper two <br />
digits (a digit having e.g. a size of 8 byte) of r by the upper digit of <br />
n and then decrements q_e in a loop until it has the correct size. <br />
Observing the number of times q_e is decremented through a control-flow <br />
revealing side-channel reveals a bias in the most significant bits of <br />
k. Depending on the curve this is either a negligible bias or a <br />
significant bias large enough to reconstruct k with lattice reduction <br />
methods. For SECP160R1, e.g., we find a bias of 15 bits.
Impact
Base Score 3.x
4.10
Severity 3.x
MEDIUM