def log(p, q):
assert curve.is_on_curve(p)
assert curve.is_on_curve(q)
sqrt_n = int(math.sqrt(curve.n)) + 1
# Compute the baby steps and store them in the 'precomputed' hash table.
r = None
precomputed = {None: 0}
for a in range(1, sqrt_n):
r = curve.add(r, p)
precomputed[r] = a
# Now compute the giant steps and check the hash table for any
# matching point.
r = q
s = curve.mult(sqrt_n, curve.neg(p))
for b in range(sqrt_n):
try:
a = precomputed[r]
except KeyError:
pass
else:
steps = sqrt_n + b
logarithm = a + sqrt_n * b
return logarithm, steps
r = curve.add(r, s)
raise AssertionError('logarithm not found')
def log(p, q):
assert curve.is_on_curve(p)
assert curve.is_on_curve(q)
sqrt_n = int(math.sqrt(curve.n)) + 1
# Compute the baby steps and store them in the 'precomputed' hash table.
r = None
precomputed = {None: 0}
for a in range(1, sqrt_n):
r = curve.add(r, p)
precomputed[r] = a
# Now compute the giant steps and check the hash table for any
# matching point.
r = q
s = curve.mult(sqrt_n, curve.neg(p))
for b in range(sqrt_n):
try:
a = precomputed[r]
except KeyError:
pass
else:
steps = sqrt_n + b
logarithm = a + sqrt_n * b
return logarithm, steps
r = curve.add(r, s)
raise AssertionError('logarithm not found')
def log(p, q):
assert curve.is_on_curve(p)
assert curve.is_on_curve(q)
start = random.randrange(curve.n)
r = curve.mult(start, p)
for x in range(curve.n):
if q == r:
logarithm = (start + x) % curve.n
steps = x + 1
return logarithm, steps
r = curve.add(r, p)
raise AssertionError('logarithm not found')
def log(p, q, counter=None):
assert curve.is_on_curve(p)
assert curve.is_on_curve(q)
# Pollard's Rho may fail sometimes: it may find a1 == a2 and b1 == b2,
# leading to a division by zero error. Because PollardRhoSequence uses
# random coefficients, we have more chances of finding the logarithm
# if we try again, without affecting the asymptotic time complexity.
# We try at most three times before giving up.
for i in range(3):
sequence = PollardRhoSequence(p, q)
tortoise = iter(sequence)
hare = iter(sequence)
# The range is from 0 to curve.n - 1, but actually the algorithm will
# stop much sooner (either finding the logarithm, or failing with a
# division by zero).
for j in range(curve.n):
x1, a1, b1 = next(tortoise)
x2, a2, b2 = next(hare)
x2, a2, b2 = next(hare)
if x1 == x2:
if b1 == b2:
# This would lead to a division by zero. Try with
# another random sequence.
break
x = (a1 - a2) * inverse_mod(b2 - b1, curve.n)
logarithm = x % curve.n
steps = i * curve.n + j + 1
return logarithm, steps
raise AssertionError('logarithm not found')
def log(p, q, counter=None):
assert curve.is_on_curve(p)
assert curve.is_on_curve(q)
# Pollard's Rho may fail sometimes: it may find a1 == a2 and b1 == b2,
# leading to a division by zero error. Because PollardRhoSequence uses
# random coefficients, we have more chances of finding the logarithm
# if we try again, without affecting the asymptotic time complexity.
# We try at most three times before giving up.
for i in range(3):
sequence = PollardRhoSequence(p, q)
tortoise = iter(sequence)
hare = iter(sequence)
# The range is from 0 to curve.n - 1, but actually the algorithm will
# stop much sooner (either finding the logarithm, or failing with a
# division by zero).
for j in range(curve.n):
x1, a1, b1 = next(tortoise)
x2, a2, b2 = next(hare)
x2, a2, b2 = next(hare)
if x1 == x2:
if b1 == b2:
# This would lead to a division by zero. Try with
# another random sequence.
break
x = (a1 - a2) * inverse_mod(b2 - b1, curve.n)
logarithm = x % curve.n
steps = i * curve.n + j + 1
return logarithm, steps
raise AssertionError('logarithm not found')
