GHSA-Q97C-8QH3-FPC6 phpseclib — non-constant-time X25519 scalar multiplication permits full private-key recovery

The pure-PHP X25519 scalar multiplication in phpseclib is not constant-time. Field addition and subtraction each perform a data-dependent conditional modular reduction, so the cost of each Montgomery-ladder step is a linear function of that step's reduction count which is a quantity determined by...