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3: Secret Sharing

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    7333
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    DNS is the system that maps human-memorable Internet domains like irs.gov to machine-readable IP addresses like \(166.123 .218 .220\). If an attacker can masquerade as the DNS system and convince your computer that irs.gov actually resides at some other IP address, it might result in a bad day for you.

    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


    This page titled 3: Secret Sharing is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Mike Rosulek (Open Oregon State) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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