Dan Boneh has written relevant papers on revocation of encryption keys, esp.
"A revocable backup system"
and
"Revocation of unread E-mail in an untrusted network"
both at http://crypto.stanford.edu/~dabo/pubs.html
The basic idea is to effectively destroy files using a two-layer key scheme. Files are encrypted using automatically generated keys. These keys are together encrypted using a master key. At user specified intervals (or manually), the keys are reencrypted with a new master key; revocation occurs by omitting the keys of the desired files. It works across archives, and supports repudiation - the file owner only knows master keys, thus can access only those files encrypted by keys encrypted in turn by the current master key, (and can say so honestly in court). Of course, old key files encrypted with old master keys should be deleted immediately and securely, and should not themselves be backed up!
Public key exchange protocols can support similar revocation of delivered content. Obviously, this only works until the content is in the clear, whether email, MP3s, DVD video...
That's why I suspect all the "might makes copyright" groups will start pushing content copy tracking...try
Slashdot Mirror
Dan Boneh has written relevant papers on revocation of encryption keys, esp.
"A revocable backup system"
and
"Revocation of unread E-mail in an untrusted network"
both at http://crypto.stanford.edu/~dabo/pubs.html
The basic idea is to effectively destroy files using a two-layer key scheme. Files are encrypted using automatically generated keys. These keys are together encrypted using a master key. At user specified intervals (or manually), the keys are reencrypted with a new master key; revocation occurs by omitting the keys of the desired files. It works across archives, and supports repudiation - the file owner only knows master keys, thus can access only those files encrypted by keys encrypted in turn by the current master key, (and can say so honestly in court). Of course, old key files encrypted with old master keys should be deleted immediately and securely, and should not themselves be backed up!
Public key exchange protocols can support similar revocation of delivered content. Obviously, this only works until the content is in the clear, whether email, MP3s, DVD video...
That's why I suspect all the "might makes copyright" groups will start pushing content copy tracking...try
"An efficient public key traitor tracing scheme"
(same URL) on for size!