Abstract (EN)

Encryption key loss problem is the Achilles's heel of cryptography. Key escrow helps, but favors disclosures. Schemes for recoverable encryption keys through noised secret sharing alleviate the dilemma. Key owner escrows a specifically encrypted backup. The recovery needs a large cloud. Cloud cost, money trail should rarefy illegal attempts. We now propose noised secret sharing schemes supporting discounts. The recovery request with discount code lowers the recovery complexity, easily by orders of magnitude. A smaller cloud may suffice for the same recovery timing. Alternatively, same cloud may provide faster recovery etc. Our schemes appear useful for users attracted to Big Data, but afraid of possibly humongous consequences of the key loss or data disclosure.