A hash is the result of running data through a mathematical function that always produces a fixed-length output, no matter how large the input. The same input always gives the same hash, but even a tiny change to the input produces a completely different result. This makes a hash act like a unique fingerprint for a piece of data.
Hashes are central to how blockchains work. Each block is identified by a hash of its contents, and each block also includes the hash of the block before it. This is what links blocks into a chain, and it is why altering an old block would change its hash and break every link that follows.
A key property is that hashing only works one way. You can easily produce a hash from data, but you cannot reverse a hash back into the original input. This one-way nature is part of what makes blockchains tamper-evident and secure.
Frequently Asked Questions
Can a hash be reversed to get the original data?
No. Hashing is a one-way process. You can produce a hash from data easily, but you cannot work backward from a hash to recover the original input.
Why does a small change create a totally different hash?
Hash functions are designed so that any change to the input, even a single character, produces a completely different output. This makes tampering easy to detect.
