# SHA-256 Hash Calculator Tool

One of the building blocks of blockchain technologies are cryptographic hash functions. This tool demonstrates the calculation of the SHA-256 hash function for linking blocks, integrity checking or higher level existence proof and notarization applications.

A hash function summarizes an arbitrary length *message* into a fixed-length *message digest* or *hash value* as in *hash(message) = hash_value*. Using SHA-256 as a hash function, any message entered below – e.g. data of a document, contract, image, certificate or any arbitrary data – is summarized by a 256 bit value.

**Message**

**Hash Value**

The resulting hash value is usually represented as hexadecial characters (up to 64 characters). For demonstration purposes, a decimal representation (up to 78 places) and binary digits (up to 256 digits) are shown additionally.

*Hexadecimal*

*Decimal*

*Binary Digits*

##### Properties of cryptographic hash functions for blockchains

As a cryptographic hash function, SHA-256 is suitable for blockchain applications to secure the integrity of data in blocks, to link a block to its predecessor and to realize higher level applications such as existence proofs. Blockchains require cryptographic hash functions, as they are one-way functions with the properties of collision resistance and preimage resistance. While it is efficient to compute the function *hash(message) = hash_value*, it is not efficient to reverse it by computing a *message* from *hash_value*. Since the length of *message* can be larger than the length of *hash_value* (given the same encoding), collisions exist, i.e. pairs of two *message* inputs with the same resulting *hash_value* output – however, it is not efficient to find such a pair of messages (collision resistance). More specifically, it is not efficient to find any *message* for a given *hash_value* (preimage resistance) and it is not efficient to derive a *message’* from an existing *message* such that both messages result in the same hash value (preimage resistance 2nd). In effect, the output of a cryptographic hash function changes unpredictably in a pseudo-random fashion when the input changes.

The hash calculations on this site are made by client-side javascript libraries in the visitors browser locally, no data entered is transmitted to the server. Libraries used on this site are jssha256.js and BigInteger.js.