Trail of Bits researchers discovered hundreds of weak RSA and DSA keys with heavily biased (zero-heavy) bits in the wild, dubbed 'short-sleeve' keys. They developed a novel polynomial-based cryptanalytic technique that reduces RSA factoring to the easier problem of polynomial factoring by exploiting the regular structure of zero-bit blocks in big-integer limbs. One pattern was traced to a type mismatch bug in CompleteFTP (EnterpriseDT) versions 10.0.0–12.0.0 for RSA and up to 23.0.4 for DSA, where Array.Copy implicitly cast 8-bit RNG output into 32-bit limbs, leaving most bits zero. The researchers recovered 603 unique RSA private keys and 74 DSA private keys from internet scans. CompleteFTP v26.1.0 now auto-detects vulnerable keys, and a standalone checker tool has been released. A second pattern affecting Yahoo and Verizon certificates remains unexplained.
