74 lines
2.4 KiB
Python
74 lines
2.4 KiB
Python
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#!/usr/bin/env python3
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import sys; assert sys.version_info[0] >= 3, "Python 3 required."
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from orchard_group_hash import group_hash
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from orchard_pallas import Fp, Scalar
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from orchard_sinsemilla import sinsemilla_hash_to_point
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from sapling_utils import i2lebsp
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# Commitment schemes used in Orchard https://zips.z.cash/protocol/nu5.pdf#concretecommit
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# https://zips.z.cash/protocol/nu5.pdf#constants
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L_ORCHARD_BASE = 255
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# https://zips.z.cash/protocol/nu5.pdf#concretehomomorphiccommit
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def homomorphic_pedersen_commitment(rcv: Scalar, D, v: Scalar):
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return group_hash(D, b"v") * v + group_hash(D, b"r") * rcv
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def value_commit(rcv: Scalar, v: Scalar):
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return homomorphic_pedersen_commitment(rcv, b"z.cash:Orchard-cv", v)
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def rcv_trapdoor(randbytes):
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return Scalar.random(randbytes)
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# https://zips.z.cash/protocol/nu5.pdf#concretesinsemillacommit
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def sinsemilla_commit(r: Scalar, D, M):
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return sinsemilla_hash_to_point(D + b"-M", M).checked_incomplete_add(
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r * group_hash(D + b"-r", "")
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)
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def sinsemilla_short_commit(r: Scalar, D, M):
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return sinsemilla_commit(r, D, M).extract()
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# https://zips.z.cash/protocol/nu5.pdf#concreteorchardnotecommit
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def note_commit(rcm, g_d, pk_d, v, rho, psi):
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return sinsemilla_commit(
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rcm,
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"z.cash: Orchard-NoteCommit",
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g_d + pk_d + i2lebsp(64, v) + i2lebsp(L_ORCHARD_BASE, rho) + i2lebsp(L_ORCHARD_BASE, psi)
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)
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def rcm_trapdoor(randbytes):
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return Scalar.random(randbytes)
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# https://zips.z.cash/protocol/nu5.pdf#concreteorchardnotecommit
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def commit_ivk(rivk, ak, nk):
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return sinsemilla_short_commit(
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rivk,
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"z.cash: Orchard-CommitIvk",
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i2lebsp(L_ORCHARD_BASE, ak) + i2lebsp(L_ORCHARD_BASE, nk)
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)
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def rivk_trapdoor(randbytes):
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return Scalar.random(randbytes)
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# Test consistency of ValueCommit^{Orchard} with precomputed generators
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def test_value_commit():
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from random import Random
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from orchard_generators import VALUE_COMMITMENT_RANDOMNESS_BASE, VALUE_COMMITMENT_VALUE_BASE
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rng = Random(0xabad533d)
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def randbytes(l):
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ret = []
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while len(ret) < l:
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ret.append(rng.randrange(0, 256))
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return bytes(ret)
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rcv = rcv_trapdoor(randbytes)
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v = Scalar(100000000)
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assert value_commit(rcv, v) == VALUE_COMMITMENT_RANDOMNESS_BASE * rcv + VALUE_COMMITMENT_VALUE_BASE * v
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if __name__ == '__main__':
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test_value_commit()
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