(from_bytes_mod_order_wide_spec, kernel-audited)
Proofs/ScalarPackSpec.lean:
- scalar52_to_bytes_spec: Scalar52::to_bytes (the PACK step - pure
bit-packing at radix 2^52, no reduction) serializes canonical limbs to
exactly their value: bytesVal s = scVal a. Second application of the
ToBytesSpec walk generator; boundary bytes 6 and 19 only (the two
non-byte-aligned 52j offsets), disjoint ORs to additions as before.
- from_bytes_mod_order_wide_spec: the verifier's k = SHA-512-to-scalar
entry composes from_bytes_wide_spec (the proven mod-l reduction) with
the pack: for 64 input bytes of value T, the returned Scalar's 32
bytes denote V with V < l and V = T (mod l) - precisely the scalar
premises vartime_double_base_mul_spec consumes (V < l < 2^253).
- byte_split_52_4: the offset-4 chunk split for 52-bit limbs; the five
ToBytesMath byte_split_* lemmas shed their unused 2^51 premises (pure
telescopes, valid for all f).
Both certificates exact-standard-three. Full button green fresh.
Half-lift remaining (mapped in memory): dsm dispatch wrapper, recompute
bind-chain inversion, bytesVal injectivity, assembly in PointLiftSpec.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
encoding of the denoted affine point (kernel-audited)
CurveFieldProofs.ed_compress_spec: for any valid extended point Pt
(ExtValid - the invariant every certified curve op guarantees),
compress Pt = ok s with
bytesVal s = (edY Pt).val + ((edX Pt).val % 2) * 2^255
- the 32 wire bytes are the canonical little-endian y-residue with the
x-parity bit at position 255. Compress semantics AND canonicity in one
statement, because to_bytes_spec pins the bytes to the residue itself.
Supporting certificates in Proofs/CompressSpec.lean:
- is_negative_spec: the sign read is the parity of the CANONICAL residue
(bit 0 of to_bytes) - (feVal x mod p) mod 2.
- Bytes32.exists_bytes: the 32-byte destructuring device (the
Fe.exists_limbs idiom, 32-wide).
- to_bytes_spec': premise-free restatement of the canonicity brick.
- xor_top_bit (ToBytesMath): setting a clear top bit by XOR is addition -
proven from xor_div_two_pow + and_xor_distrib_right, no bit-blasting.
The chain is entirely certified code: invert (Fermat), two muls, to_bytes
(canonicity), is_negative, and the sign-bit XOR. Axiom cone of
ed_compress_spec: exactly [propext, Classical.choice, Quot.sound].
check.sh: CompressSpec in PROOFS, ed_compress_spec in CERTS - full button
green fresh.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
The load-bearing brick of the point-level apex equation:
FieldElement51::to_bytes always succeeds and its 32 output bytes denote
EXACTLY the represented residue - bytesVal s = feVal a mod p. Since the
canonical residue determines the bytes, this is simultaneously
canonicity ("output is the canonical encoding") and the injectivity
compress needs ("equal residues iff equal bytes").
- Proofs/ToBytesMath.lean: the context-free ℕ mathematics (METHOD 4) -
the 5-rung carry telescope (div_rung/q_telescope), the q-trick facts
(q = (h+19)/2^255 is a bit, fires iff h >= p), q_mod_p (adding 19q and
discarding bit 255 subtracts pq exactly), carry_pack (the masked-limb
assembly mod 2^255), five per-limb byte-chunk splits, and bytes_pack
(the 32-byte little-endian reassembly, closed by one zify +
linear_combination over the five splits).
- Proofs/ToBytesSpec.lean: the symbolic execution - at ~150 machine ops
the longest walk in the repo, loop-free: weak reduce (reduce_spec),
the q pass, the fold + carry pass, 32 byte extractions (the four
limb-boundary bytes turn disjoint ORs into additions via
Nat.two_pow_add_eq_or_of_lt), and the trailing top-bit debug-assert
DISCHARGED (b31 = f4/2^44 < 2^7), not assumed.
- check.sh: ToBytesMath/ToBytesSpec in PROOFS, to_bytes_spec in CERTS
(exact standard-three audit) - full button green fresh.
Walk lessons (for the control repo, next push): rw index-equations into
their consumers instead of subst (subst eliminates the wrong side or
dies on dependent do-motives); never rw [Nat.mod_eq_of_lt (by omega)]
(metavariable goal reaches omega) - state the bound with show.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
