So, the reason I asked about "orthogonal checksums" was this: If you can check the integrity of a copy of a file remotely, then people can trade storage space and have remote backups. Or have more complicated schemes where, say, a group of users pay for a common storage service by backing up some of the files (or other files) for the provider. The nice thing about this is that storage space is something that's immediately valuable and electronically tradable. And its value can increase by trading. In other words, we can trade one meg for one meg and both come out ahead in terms of safety. "I back your scratch and you back mine." I'm not sure storage space makes a good unit of value for anything else, since the cost of storage keeps going down. On the other hand, trading space for space is immune to that inflation. Some concrete applications: o Making bulletin boards' data safe from loss by vandalism o Archiving a mailing list -fnerd - - - - - - - - - - - - - - - nowhere man has gone before -----BEGIN PGP SIGNATURE----- Version: 2.3a aKxB8nktcBAeQHabQP/d7yhWgpGZBIoIqII8cY9nG55HYHgvt3niQCVAgUBLMs3K ui6XaCZmKH68fOWYYySKAzPkXyfYKnOlzsIjp2tPEot1Q5A3/n54PBKrUDN9tHVz 3Ch466q9EKUuDulTU6OLsilzmRvQJn0EJhzd4pht6hSnC1R3seYNhUYhoJViCcCG sRjLQs4iVVM= =9wqs -----END PGP SIGNATURE-----