Vanishing digital signatures

It may sometimes be useful to digitally sign some data in a way such that your signature automatically disappears after a predetermined length of time. I had previously imagined DCKR being used in conjunction with a Satoshi-style block chain, so that the block chain's chain of hashes linking back to the past would compliment the signature key chain linking into the future, thus all historical data could be verified at any time. But simply by using DCKR outside the context of a conventional block chain, you can have signatures whose validity automatically expires - and that might sometimes be a useful effect.

I should also suggest a few tweaks to the original version either with or without use within a block chain construct. First, it should not be necessary to include previously used keys with the message being signed. Second, it may be useful to have several parallel chains of keys, scheduled to be reveled at different intervals, so as to simultaneously accommodate a range of timeliness versus latency requirements. Also, more sophisticated implementations might find it useful to include a mechanism for adjusting the release schedule of one or more chains of keys, or for scheduling the transition to or addition of new chains of keys, possibly using different hash functions - simply by precommitting to these changes within the signed structures.