Survey on Remote Electronic Voting <s> C. Blind Signatures + Secret Sharing <s> Certain cryptographic keys, such as a number which makes it possible to compute the secret decoding exponent in an RSA public key cryptosystem,1,5 or the system master key and certain other keys in a DES cryptosystem,3 are so important that they present a dilemma. If too many copies are distributed one might go astray. If too few copies are made they might all be destroyed. A typical cryptosystem will have several volatile copies of an important key in protected memory locations where they will very probably evaporate if any tampering or probing occurs. Since an opponent may be content to disrupt the system by forcing the evaporation of all these copies it is useful to entrust one or more other nonvolatile copies to reliable individuals or secure locations. What must the nonvolatile copies of the keys, or nonvolatile pieces of information from which the keys are reconstructed, be guarded against? The answer is that there are at least three types of incidents: <s> BIB001 </s> Survey on Remote Electronic Voting <s> C. Blind Signatures + Secret Sharing <s> In this paper we show how to divide data D into n pieces in such a way that D is easily reconstructable from any k pieces, but even complete knowledge of k - 1 pieces reveals absolutely no information about D . This technique enables the construction of robust key management schemes for cryptographic systems that can function securely and reliably even when misfortunes destroy half the pieces and security breaches expose all but one of the remaining pieces. <s> BIB002
Blind Signatures Assume Alice wants Bob to sign her message, but she does not want him to read this message. With blind signatures Alice would encrypt her message m with her private key as known from RSA but add a random factor to this encryption and send the resultm to Bob. He may have Alice's public key, but because of the random factor he is not able to read this message. After Bob signs the message sig(m) and sends it back to Alice, she is able to remove the random factor and has a signature for her message sig(m). So Alice can get a valid signature for her message from Bob, but he was not able to decrypt her message. Secret Sharing Secret sharing mechanisms described in BIB002 BIB001 can be used to divide a secret into pieces and distribute it to n different entities. To reconstruct the secret, t of n entities need to cooperate. In the context of electronic voting this threshold scheme can ensure that at least t entities must be corrupted to gain access to the secret, e.g. the secret key of the ballot to decrypt the votes.