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Add NonIdentityPoint::new_from_constant#56

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ConstanceBeguier wants to merge 1 commit into
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add_non_identity_constant_point
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Add NonIdentityPoint::new_from_constant#56
ConstanceBeguier wants to merge 1 commit into
mainfrom
add_non_identity_constant_point

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This PR adds NonIdentityPoint::new_from_constant to enable creating non-identity points that are properly pinned to constants, which is required by the Orchard ZSA circuit (Orchard PR).

More precisely, in the Orchard ZSA circuit, q_init_zec / q_init_zsa must be constrained to fixed constants, as they define the initial point Q of the Sinsemilla hash. If constructed via NonIdentityPoint::new, they remain unconstrained witnesses, allowing a prover to inject an arbitrary on-curve point and break commitment soundness.

This PR adds `NonIdentityPoint::new_from_constant` to enable creating non-identity points that are properly pinned to constants, which is required by the Orchard ZSA circuit ([Orchard PR](QED-it/orchard#246)).

More precisely, in the Orchard ZSA circuit, `q_init_zec` / `q_init_zsa` must be constrained to fixed constants, as they define the initial point `Q` of the Sinsemilla hash. If constructed via `NonIdentityPoint::new`, they remain unconstrained witnesses, allowing a prover to inject an arbitrary on-curve point and break commitment soundness.
@ConstanceBeguier ConstanceBeguier requested review from PaulLaux and removed request for PaulLaux May 4, 2026 12:51
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