Daniel Crowley - Key Search Attacks Against Modern Symmetric Ciphers
Revisits meet-in-the-middle and other key search attacks against symmetric ciphers, examining their relevance to modern key length choices.
Summary
Key Search Attacks on Symmetric Ciphers
Daniel Crowley (Research Director, IBM X-Force Red) presents a comprehensive examination of key search attacks targeting symmetric block ciphers, assessing their practical viability against current key lengths.
Meet-in-the-Middle Attacks
The classical meet-in-the-middle attack against 2DES reduces the effective key space from 2^112 to 2^56 with a time-memory tradeoff. Crowley examines modern variants that extend this to triple-key constructions and analyze whether similar weaknesses apply to AES key scheduling.
Distributed Key Search Infrastructure
Using cloud GPU instances (AWS p3 instances with V100s), Crowley demonstrates cost-effective key search against weak key lengths, quantifying the cost to brute-force 56-bit and 64-bit keys in current dollars.
Key Length Recommendations
The talk concludes with practical guidance on minimum key lengths for symmetric ciphers given current and projected hardware capabilities, providing 10-, 20-, and 30-year threat horizons.
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