A cryptographic hash function is a special type of function that takes an input string of a given length and converts it to a fixed-length alphanumeric string.
In the case of Bitcoin, the input is a “message” and the output is a “hash” produced by a hash function, known as SHA-256 (Secure Hashing Algorithm 256). This means that regardless of the length of the data string (within the limit of 2²⁵⁶- 1 bits), the output will always be 256 bits long. The hashing process is not an encryption method as it is only a one-way process and therefore cannot be reversed (decrypted). By calculating multiple outputs with SHA-256, we find that changing a single character of the message gives completely different outputs. We also find that no matter how long the message is, the output will always be the same length.
SHA-256 is also a deterministic function, which means that the same input will always give the same output.
