(One-way) It is computationally infeasible to find any input that maps to any pre-specified output, andĢ. Approved hash functions are designed to satisfy the following properties:ġ. 1 under Hash function A function that maps a bit string of arbitrary length to a fixed length bit string. Second preimage resistance (see Second preimage resistance).Īpproved hash functions are specified in. Preimage resistance (see Preimage resistance) andģ. Collision resistance (see Collision resistance),Ģ. The function is expected to have the following three properties:ġ. Source(s): NIST SP 800-106 under Cryptographic hash function A function that maps a bit string of arbitrary length to a fixed-length bit string. Member functions operator() Returns a hash value for its argument, as a value of type size_t.A function that maps a bit string of arbitrary length to a fixed length bit string and is expected to have the following three properties:ġ) Collision resistance (see Collision resistance),Ģ) Preimage resistance (see Preimage resistance) andģ) Second preimage resistance (see Second preimage resistance).Īpproved cryptographic hash functions are specified in. The type of the values taken as argument. Users can provide custom specializations for this template with these same properties. But all library implementations provide at least the following type-specific specializations:Īpart from being callable with an argument of the appropriate types, all objects of hash instantiations are default-constructible, copy-constructible, copy-assignable, destructible and swappable. The default hash is a template class that is not defined for the general case. Other function object types can be used as Hash for unordered containers provided they behave as defined above and they are at least copy-constructible, destructible function objects. The value returned shall have a small likelihood of being the same as the one returned for a different argument (with chances of collision approaching 1/ numeric_limits::max). The functional call returns a hash value of its argument: A hash value is a value that depends solely on its argument, returning always the same value for the same argument (for a given execution of a program). Unary function object class that defines the default hash function used by the standard library.

String hash functions