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create a fast modular exponent function #209

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create a fast modular exponent function #209

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ac92910
create a fast modular exponent function
krishnajalan Aug 28, 2020
f8b3f11
change range to xrange
krishnajalan Aug 28, 2020
214e458
remove extra for loop
krishnajalan Aug 28, 2020
9226ce3
fast modular exponent
krishnajalan Aug 31, 2020
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19 changes: 17 additions & 2 deletions src/ecdsa/numbertheory.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,8 +62,23 @@ def modular_exp(base, exponent, modulus): # pragma: no cover
raise NegativeExponentError(
"Negative exponents (%d) not allowed" % exponent
)
return pow(base, exponent, modulus)

if (type(exponent)==int):
return fast_modular_exponentiation(base, exponent, modulus)
else:
return pow(base, exponent, modulus)

def fast_modular_exponentiation(base, exponent, modulas):

"""Log(N) computation required to find the final Exponent"""
binary = bin(exponent)[-1:1:-1]
l = {}
ans = 1
for i in range(len(binary)):
l[i] = base
base = (base**2)%modulas
if binary[i]=='1':
ans *= l[i]%modulas
return ans%modulas

def polynomial_reduce_mod(poly, polymod, p):
"""Reduce poly by polymod, integer arithmetic modulo p.
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