On Mon, Jun 07, 2010, Jason Fister wrote: > Hello folks, > > I have a service to which people can send data. My service then stores the > data and returns the SHA checksum for the data back to the client. I also > store the checksum I computed and the offset at which it was computed as > part of the metadata. > > I want to allow clients to send append requests to this data at a later > time. When they send the append request, I want to be able to use the > checksum that I had already calculated as the starting point and then use > that to generate the new checksum for the appended object. > > I know about the init, update and final functions. But I dont see a way to > pass in the checksum value of the original object when computing the > checksum of the new appended object. > > Can someone tell me how I can achive the above? >
You mean you want to do: SHA1(A) and later do: SHA1(A || B) without including A again? The hash itself does not contain enough information to continue in that fashion. You'd need to store the actual hash context. There isn't a standard OpenSSL function to this you'd need to delve into the internals a little and copy the flat context somewhere and later restore. So you'd do something like... init update(A) save_context hash_A = final init restore_context update(B) hash_AB=final Steve. -- Dr Stephen N. Henson. OpenSSL project core developer. Commercial tech support now available see: http://www.openssl.org ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
