MD5CRK

In cryptography, MD5CRK was a volunteer computing effort (similar to distributed.net) launched by Jean-Luc Cooke and his company, CertainKey Cryptosystems, to demonstrate that the MD5 message digest algorithm is insecure by finding a collision – two messages that produce the same MD5 hash. The project went live on March 1, 2004. The project ended on August 24, 2004 after researchers independently demonstrated a technique for generating collisions in MD5 using analytical methods by Xiaoyun Wang, Feng, Xuejia Lai, and Yu.^[1] CertainKey awarded a 10,000 Canadian Dollar prize to Wang, Feng, Lai and Yu for their discovery.^[2]

A technique called Floyd's cycle-finding algorithm was used to try to find a collision for MD5. The algorithm can be described by analogy with a random walk. Using the principle that any function with a finite number of possible outputs placed in a feedback loop will cycle, one can use a relatively small amount of memory to store outputs with particular structures and use them as "markers" to better detect when a marker has been "passed" before. These markers are called distinguished points, the point where two inputs produce the same output is called a collision point. MD5CRK considered any point whose first 32 bits were zeroes to be a distinguished point.

Complexity

The expected time to find a collision is not equal to ${\displaystyle 2^{N}}$ where ${\displaystyle N}$ is the number of bits in the digest output. It is in fact ${\displaystyle 2^{N}! \over {(2^{N}-K)!\times {2^{N}}^{K}}}$, where ${\displaystyle K}$ is the number of function outputs collected.

For this project, the probability of success after ${\displaystyle K}$ MD5 computations can be approximated by: ${\displaystyle 1 \over {1-e^{K\times (1-K) \over 2^{N+1}}}}$.

The expected number of computations required to produce a collision in the 128-bit MD5 message digest function is thus: ${\displaystyle {1.17741\times 2^{N/2}}={1.17741\times 2^{64}}}$

To give some perspective to this, using Virginia Tech's System X with a maximum performance of 12.25 Teraflops, it would take approximately ${\displaystyle {2.17\times 10^{19}/12.25\times 10^{12}\approx 1,770,000}}$ seconds or about 3 weeks. Or for commodity processors at 2 gigaflops it would take 6,000 machines approximately the same amount of time.

See also

• List of volunteer computing projects
• Brute force attack

References

Further reading

• Paul C. van Oorschot; Michael J. Wiener. Parallel Collision Search with Application to Hash Functions and Discrete Logarithms (PDF). ACM Conference on Computer and Communications Security 1994. pp. 210–218.