PuTTY ECDSA Nonce Bias: How 71 Signatures Exposed Your SSH Key
PuTTY's April 2024 advisory for CVE-2024-31497 read like a physics problem: the terminal's ECDSA implementation biased nonces on NIST P-521, so roughly 71 captured SSH signatures suffice for a lattice attack that recovers the private key. This piece explains the Hidden Number Problem math, why archived PCAP and DLP session capture retroactively weaponized years of traffic, the 0.81 deterministic-nonce fix, and the brutal rotation drill that made every P-521 key used through Pageant presumptively burned.