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collision test for iterated, truncated sha1
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gistfile1.py
import hashlib
def H(s):
for i in xrange(N):
s = hashlib.sha1(s).hexdigest()[:4]
return s
n = 1000000
for N in range(1, 17):
collisions = 0
for i in xrange(n):
collisions += H('a%dN%d' % (i, N)) == H('b%dN%d' % (i, N))
print N, int(n * 1. / collisions)
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jvarho commented Jun 18, 2014

Used for this Crypto Stackexchange answer. Plot here.

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