I'd like to completely delete an address from bitcoin-core, in such a way that someone who obtains all the data on my computer could not find out I ever used that address.
Is it enough to delete
wallet.dat? Is there a less destructive way?
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No, and in fact, deleting a file is not destructive enough.
File deletion typically does not actually delete the file. Filesystems will just mark a file as deleted and allow it to be overwritten. If the file does not end up overwritten, it can be recovered from the drive using some forensic tools.
Furthermore, the way that the hard drive itself writes data physically often leads to data being left behind and just marked to be overwritten. So there could actually be multiple copies and fragments of your wallet.dat file left on the hard drive. Forensic analysis tools can then recover those fragments even after the file has been deleted, and some portions overwritten.
A better guarantee that no one can recover the data is to wipe the hard drive and overwrite every part of it with random data. However there is the potential for bad sectors or other issues with the drive which prevents an overwrite from actually overwriting some portions of the drive.
To be absolutely sure that data cannot be recovered, you have to do what companies like Google do to ensure that data cannot be recovered from their used drives: completely destroy the physical drive. Physical destruction is actually the only way to ensure that no data can be recovered from a drive.