A function on bit strings in which the output can be extended to any desired length. Approved XOFs (e.g., those specified in FIPS 202) are designed to satisfy the following properties as long as the specified output length is sufficiently long to prevent trivial attacks 1. (One-way) It is computationally infeasible to find any input that maps to any new pre-specified output. 2. (Collision-resistant) It is computationally infeasible to find any two distinct inputs that map to the same output.
Sources:
FIPS 204
under eXtendable-Output Function (XOF)
A function on bit strings in which the output can be extended to any desired length.
Sources:
NIST SP 800-185
under eXtendable-Output Function (XOF)