AbstractHash functions are one-way functions that map arbitrary-length input to fixed-length output. Moreover, they have many cryptographic applications, such as integrity checks, password storage, and signatures. Cryptographic hash functions have some additional properties that can be formulated as hard problems: pre-image resistance, second pre-image resistance, and collision resistance. A significant technological development in this area is unlikely. Standardized hash functions are considered secure, and open-source implementations can be used at no cost. To conclude, the security properties required from hash functions depend on the intended purpose.