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3: Secret Sharing

Last updated

Dec 12, 2022
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- 2.6: Exercise
- 3.1: Definitions

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To protect against these kinds of attacks, a replacement called DNSSEC has been proposed. DNSSEC uses cryptography to make it impossible to falsify a domain-name mapping. The cryptography required to authenticate DNS mappings is certainly interesting, but an even more fundamental question remains: Who can be trusted with the master cryptographic keys to the system? The non-profit organization in charge of these kinds of things (ICANN) has chosen the following system. The master key is split into 7 pieces and distributed on smart cards to 7 geographically diverse people, who keep them in safe-deposit boxes.

At least five key-holding members of this fellowship would have to meet at a secure data center in the United States to reboot [DNSSEC] in case of a very unlikely system collapse.

"If you round up five of these guys, they can decrypt [the root key] should the West Coast fall in the water and the East Coast get hit by a nuclear bomb," [said] Richard Lamb, program manager for DNSSEC at ICANN. ${ }^{1}$

How is it possible that any 5 out of the 7 key-holders can reconstruct the master key, but (presumably) 4 out of the 7 cannot? The solution lies in a cryptographic tool called a secret-sharing scheme, the topic of this chapter.

${ }^{1}$ http://www.livescience.com/6791-internet-key-holders-insurance-cyber-attack.html

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