About
git uses as identifier for any object a message digest
The hash is known as hash object because the whole git system is based on objects
This hash is the unique key that is used in the database
It's also called an extended SHA-1 syntax.
Where is the Git Hash function ?
The function is available via the hash-object command
Example for a blob
echo 'test content' | git hash-object -w --stdin
d670460b4b4aece5915caf5c68d12f560a9fe3e4