Digital preservation: checksum

A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, it's assumed that the complete transmission was received. Both TCP and UDP communication layers provide a checksum count and verification as one of their services (Definition by SearchSecurity of network of technology TechTarget).

This blog post and video provide a good introduction to checksums in the context of digital preservation.
See this blog post for some advice on possible  tools.
See concept of significant properties and digital preservation of  InSPECT (Investigating the Significant Properties of Electronic Content Over Time)