Threshold cryptosystem

A threshold cryptosystem, the basis for the field of threshold cryptography, is a cryptosystem in which the secret key is split into a number of pieces that are given to different parties. Several parties (more than some threshold number) can then cooperate to use the cryptosystem.

More precisely, let be the number of parties. A cryptosystem is called (t,n)-threshold, if at least t of these parties can cooperate to perform the desired operation (usually sign a message or decrypt a ciphertext), while any subset of fewer than t parties cannot.

Threshold cryptography allows to store secrets in multiple locations to prevent the capture of the secret and the subsequent cryptanalysis of that system. This makes the method a primary trust sharing mechanism, besides its safety of storage aspects.

Constructions for threshold cryptosystems often combine an existing non-threshold cryptosystem with a secret sharing.

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