Increased DNS Forgery Resistance Through 0x20-Bit Encoding

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Executive Summary

It describe a novel, practical and simple technique to make DNS queries more resistant to poisoning attacks: mix the upper and lower case spelling of the domain name in the query. Fortuitously, almost all DNS authority servers preserve the mixed case encoding of the query in answer messages. Attackers hoping to poison a DNS cache must therefore guess the mixed-case encoding of the query, in addition to all other fields required in a DNS poisoning attack. This increases the difficulty of the attack. It describes and measures the additional protections realized by this technique. The analysis includes a basic model of DNS poisoning, measurement of the benefits that come from case-sensitive query encoding, implementation of the system for recursive DNS servers, and large-scale real-world experimental evaluation.

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