Robin sez
Dorn suggests:
The servers would generate a key pair on request, for a fee. Send you the public key to encrypt the "message" for storage somewhere.
I guess this might work, but now you have to be more specific in telling your escrow service where to look for public keys to decode you message. With just a few standard time-key servers, this isn't needed, and perhaps we could all share the costs of monitoring their trustworthyness. Needing just a few, the need might easily be met by charity.
The escrow services could run the time-key servers (since without the time-key servers, there would be less business for the escrow services). Getting keys would then be free and the cost of running the server could be subsidised from the cost of storing the message. corwin