Difficulty of finding another input string that hashes to the same value as a given string
Second preimage resistance is a security property of cryptographic hash functions. A hash function $H$ is said to be second preimage resistant if, given an input string $s$, it is computationally infeasible to find another string $s' \ne s$ such that $H(s') = H(s)$.
Second preimage resistance is a stronger security property than first preimage resistance, but weaker than collision resistance.
See also: preimage-resistance, collision-resistance
