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feat(python): add elligator2

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This commit is contained in:
M1nd3r 2025-01-30 18:14:52 +01:00
parent 66334eab4d
commit 1d1f670a18
1 changed files with 43 additions and 0 deletions
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43
python/src/trezorlib/transport/thp/curve25519.py
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@ -114,3 +114,46 @@ def multiply(private_scalar: bytes, public_point: bytes):
x = pow(z_2, p - 2, p) * x_2 % p
return encode_coordinate(x)
def elligator2(point: bytes) -> bytes:
# map_to_curve_elligator2_curve25519 from
# https://www.rfc-editor.org/rfc/rfc9380.html#ell2-opt
def conditional_move(first: int, second: int, condition: bool):
# Returns second if condition is true and first otherwise
# Must be implemented in a way that it is constant time
true_mask = -condition
false_mask = ~true_mask
return (first & false_mask) | (second & true_mask)
u = decode_coordinate(point)
tv1 = (u * u) % p
tv1 = (2 * tv1) % p
xd = (tv1 + 1) % p
x1n = (-J) % p
tv2 = (xd * xd) % p
gxd = (tv2 * xd) % p
gx1 = (J * tv1) % p
gx1 = (gx1 * x1n) % p
gx1 = (gx1 + tv2) % p
gx1 = (gx1 * x1n) % p
tv3 = (gxd * gxd) % p
tv2 = (tv3 * tv3) % p
tv3 = (tv3 * gxd) % p
tv3 = (tv3 * gx1) % p
tv2 = (tv2 * tv3) % p
y11 = pow(tv2, c4, p)
y11 = (y11 * tv3) % p
y12 = (y11 * c3) % p
tv2 = (y11 * y11) % p
tv2 = (tv2 * gxd) % p
e1 = tv2 == gx1
y1 = conditional_move(y12, y11, e1)
x2n = (x1n * tv1) % p
tv2 = (y1 * y1) % p
tv2 = (tv2 * gxd) % p
e3 = tv2 == gx1
xn = conditional_move(x2n, x1n, e3)
x = xn * pow(xd, p - 2, p) % p
return encode_coordinate(x)