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 pr

Answer 1

A checksum is simply a number generated from the data field by oring(by logical addition hence sum). The checksum has the capability to detect a corruption of any bit or number of bits within the data field from which it is generated ie it checks for errors that is all, it can not correct them. A checksum is a hash because the size of the checksum is smaller than the original data. Yes you will have collisions because the checksum is not at all sensitive to bit position in the data field.

A cyclic redundancy check ( CRC) is something quite different , more complex and is NOT called a checksum. It is the application of a polynomial series which has the capability of correcting any chosen number of individual corrupted bits within the data field from which it was generated. The creation of a CRC results in a number greater in size than the original datafield (unlike the checksum) - hence the name including the word "redundancy" and the price you pay for the error correcting capability. A CRC is therefore NOT a hash and must not be confused or named as a checksum , because the redundancy necessarily adds to the size of the original data.