Hash Code and Checksum - what's the difference?

Question

My understanding is that a hash code and checksum are similar things - a numeric value, computed for a block of data, that is *relatively* unique.i.e. The probability of two blocks of data yielding the same numeric hash/checksum value is low enough that it can be ignored for the purposes of the application.So do we have two words for the same thing, or are there important differences between hash codes and checksums?

Answer 1

A checksum (such as CRC32) is to prevent accidental changes. If one byte changes, the checksum changes. The checksum is not safe to protect against malicious changes: it is pretty easy to create a file with a particular checksum.

A hash function maps some data to other data. It is often used to speed up comparisons or create a hash table. Not all hash functions are secure and the hash does not necessarily changes when the data changes.

A cryptographic hash function (such as SHA1) is a checksum that is secure against malicious changes. It is pretty hard to create a file with a specific cryptographic hash.

To make things more complicated, cryptographic hash functions are sometimes simply referred to as hash functions.