Comment on SHA-256 Certificates Are ComingparentComments−agl12yAssuming that SHA-256 is sound, then the effort needed to find a collision is 2^128.However efficient your hardware is, multiplying the energy-per-hash by 2^128 results in an impossible number.Let's say that you have a magic device that computes the total, current Bitcoin hashing rate (75 million GH/s) with just a watt of power.# Total hashes per second>> 75 * 1000000 * 100000000075000000000000000# Energy/sec over hashes/sec gives energy/hash in joules.>> float(1) / _1.3333333333333333e-17# Energy to find a collision.>> _*(1<<128)4.537098225612513e+21That's roughly "estimated energy contained in the world's natural gas reserves as of 2010": http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy) or ten years of "total world annual energy consumption in 2010".
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Assuming that SHA-256 is sound, then the effort needed to find a collision is 2^128.
However efficient your hardware is, multiplying the energy-per-hash by 2^128 results in an impossible number.
Let's say that you have a magic device that computes the total, current Bitcoin hashing rate (75 million GH/s) with just a watt of power.
# Total hashes per second
75000000000000000
# Energy/sec over hashes/sec gives energy/hash in joules.
1.3333333333333333e-17
# Energy to find a collision.
4.537098225612513e+21
That's roughly "estimated energy contained in the world's natural gas reserves as of 2010": http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy) or ten years of "total world annual energy consumption in 2010".