incremental/delta backup

[Gautamjit Kanwar]

i need to write a remote backup software application (over the internet like 
www.backupnet.com). but i am having a real hard time finding the algorithm 
for calculating the changed parts since last backup (the delta).

it seems rdiff-backup uses the same technology internally, can someone 
please point me to resources on the internet for delta calculation and 
implementation.

thanks in advance,

gautamjit

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