mirror of
https://github.com/saymrwulf/fips205-slhdsa-verified.git
synced 2026-09-04 20:03:44 +00:00
226 lines
10 KiB
Text
226 lines
10 KiB
Text
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/- Proofs/XmssSpec.lean — XMSS public-key-from-signature (Algorithm 10), the
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authentication-path Merkle loop.
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THEOREM xmss_loop_eq: the extracted auth-path loop
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(xmss_pk_from_sig_free_loop) equals the explicit fold that, at step k,
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sets the tree height to k+1, tests bit k of the leaf index, and on an even
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bit halves the tree index and hashes H(node ∥ auth[k]), on an odd bit sets
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the tree index to (i−1)/2 and hashes H(auth[k] ∥ node) — the FIPS 205
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Merkle-path recomputation. This is the layer above WOTS+: it pins the
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hash ORDER (the even/odd sibling rule), the tree-height/tree-index address
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schedule, and the auth-path indexing. H stays opaque
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(verify_mono.oracle.h), so the certificate cone is the three kernel axioms
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+ oracle.h, audited by check.sh Phase 3.
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The proof is the chain/wots recipe on a u32 range (u32_succ / fwd_succ /
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hnext and loop_unfold_bind reused VERBATIM from ChainSpec), with one new
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feature: the loop body branches on the index bit, so the step lemma and
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the induction split with by_cases + if_pos/if_neg and thread the IH under
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the opaque binds of BOTH branches with bind_congr. The get_tree_index
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pair-bind destructures with rintro; differing pair matchers are
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definitionally bridged by structure eta.
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-/
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import Proofs.ChainSpec
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open Aeneas Aeneas.Std Result ControlFlow
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open fips205
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set_option maxHeartbeats 4000000
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namespace fips205
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/-- The loop body on a non-empty range, as a clean do-block: the iterator is
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resolved (hnext) and both occurrences of start+1 — the iterator's forward
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step and the body's tree-height argument — are the same successor w. -/
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theorem hbody_x {HP N : Std.Usize} (idx : Std.U32) (pk_seed : Slice Std.U8)
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(auth : Array (Array Std.U8 N) HP) (start stop w : Std.U32)
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(adrs : types.Adrs) (node : Array Std.U8 N)
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(hd : decide (start.val < stop.val) = true) (hwok : start + 1#u32 = ok w) :
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verify_mono.xmss_pk_from_sig_free_loop.body idx pk_seed auth
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{ start := start, «end» := stop } adrs node
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= (do
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let adrs1 ← helpers.Adrs.set_tree_height adrs w
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let i1 ← idx >>> start
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let i2 ← lift (i1 &&& 1#u32)
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if i2 = 0#u32
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then
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let tmp ← i3 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let s0 ← lift (Array.to_slice node)
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let i4 ← lift (UScalar.cast .Usize start)
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let a ← Array.index_usize auth i4
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let s1 ← lift (Array.to_slice a)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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ok (cont (({ start := w, «end» := stop } : core.ops.range.Range Std.U32), adrs3, node1))
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else
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let i4 ← i3 - 1#u32
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let tmp ← i4 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let i5 ← lift (UScalar.cast .Usize start)
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let a ← Array.index_usize auth i5
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let s0 ← lift (Array.to_slice a)
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let s1 ← lift (Array.to_slice node)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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ok (cont (({ start := w, «end» := stop } : core.ops.range.Range Std.U32), adrs3, node1))) := by
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unfold verify_mono.xmss_pk_from_sig_free_loop.body
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rw [hnext hd hwok]
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simp [hwok]
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/-- The mathematical Merkle-path fold: at step k set the tree height to k+1,
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test bit k of idx, and hash the current node with auth[k] in the order
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the bit dictates, halving the tree index. Recursion on the step count;
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the successor and the fallible scalar ops stay monadic, mirroring the
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extracted code exactly. -/
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noncomputable def xmssFoldN {HP N : Std.Usize} (idx : Std.U32)
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(pk_seed : Slice Std.U8) (auth : Array (Array Std.U8 N) HP) :
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types.Adrs → Array Std.U8 N → Std.U32 → Nat → Result (Array Std.U8 N)
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| _, node, _, 0 => ok node
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| adrs, node, k, (s+1) => do
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let w ← k + 1#u32
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let adrs1 ← helpers.Adrs.set_tree_height adrs w
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let i1 ← idx >>> k
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let i2 ← lift (i1 &&& 1#u32)
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if i2 = 0#u32
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then
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let tmp ← i3 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let s0 ← lift (Array.to_slice node)
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let i4 ← lift (UScalar.cast .Usize k)
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let a ← Array.index_usize auth i4
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let s1 ← lift (Array.to_slice a)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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xmssFoldN idx pk_seed auth adrs3 node1 w s
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else
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let i4 ← i3 - 1#u32
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let tmp ← i4 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let i5 ← lift (UScalar.cast .Usize k)
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let a ← Array.index_usize auth i5
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let s0 ← lift (Array.to_slice a)
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let s1 ← lift (Array.to_slice node)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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xmssFoldN idx pk_seed auth adrs3 node1 w s
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/-- One full loop step on a non-empty range = one fold step, tail as the
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continuation loop — in BOTH branches of the index-bit test. -/
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theorem xmss_loop_step {HP N : Std.Usize} (idx : Std.U32) (pk_seed : Slice Std.U8)
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(auth : Array (Array Std.U8 N) HP) (start stop : Std.U32)
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(adrs : types.Adrs) (node : Array Std.U8 N)
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(hlt : start.val < stop.val) (hb : start.val + 1 < 2 ^ 32) :
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verify_mono.xmss_pk_from_sig_free_loop { start := start, «end» := stop }
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idx pk_seed adrs auth node
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= (do
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let w ← start + 1#u32
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let adrs1 ← helpers.Adrs.set_tree_height adrs w
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let i1 ← idx >>> start
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let i2 ← lift (i1 &&& 1#u32)
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if i2 = 0#u32
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then
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let tmp ← i3 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let s0 ← lift (Array.to_slice node)
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let i4 ← lift (UScalar.cast .Usize start)
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let a ← Array.index_usize auth i4
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let s1 ← lift (Array.to_slice a)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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verify_mono.xmss_pk_from_sig_free_loop { start := w, «end» := stop }
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idx pk_seed adrs3 auth node1
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else
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let (i3, adrs2) ← helpers.Adrs.get_tree_index adrs1
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let i4 ← i3 - 1#u32
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let tmp ← i4 / 2#u32
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let adrs3 ← helpers.Adrs.set_tree_index adrs2 tmp
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let i5 ← lift (UScalar.cast .Usize start)
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let a ← Array.index_usize auth i5
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let s0 ← lift (Array.to_slice a)
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let s1 ← lift (Array.to_slice node)
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let node1 ← verify_mono.oracle.h N pk_seed adrs3 s0 s1
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verify_mono.xmss_pk_from_sig_free_loop { start := w, «end» := stop }
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idx pk_seed adrs3 auth node1) := by
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obtain ⟨w, hwok, _⟩ := u32_succ hb
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have hd : decide (start.val < stop.val) = true := by simp [hlt]
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conv_lhs => rw [verify_mono.xmss_pk_from_sig_free_loop, loop_unfold_bind]
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dsimp only
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rw [hbody_x idx pk_seed auth start stop w adrs node hd hwok]
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simp only [bind_assoc, bind_ok]
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conv_rhs => rw [show (start + 1#u32) = ok w from hwok]
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simp only [bind_tc_ok, bind_ok]
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apply bind_congr; intro adrs1
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apply bind_congr; intro i1
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apply bind_congr; intro i2
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by_cases hc : i2 = 0#u32
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-- Per branch: expose the pair-bind (assoc), make the scrutinee concrete
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-- (bind_congr + rintro), then FULL simp: only full simp iota-reduces the
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-- pair matcher (the chain lesson); with assoc, ok-bind, and the loop def
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-- both sides normalize to the same right-nested chain.
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· rw [if_pos hc, if_pos hc]
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simp only [bind_assoc, bind_ok]
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apply bind_congr; rintro ⟨i3, adrs2⟩
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simp [bind_assoc, bind_ok, verify_mono.xmss_pk_from_sig_free_loop]
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· rw [if_neg hc, if_neg hc]
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simp only [bind_assoc, bind_ok]
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apply bind_congr; rintro ⟨i3, adrs2⟩
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simp [bind_assoc, bind_ok, verify_mono.xmss_pk_from_sig_free_loop]
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/-- **Algorithm 10 fidelity.** The extracted XMSS auth-path loop over
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[start, start+s) equals the explicit Merkle-path fold. -/
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theorem xmss_loop_eq {HP N : Std.Usize} (idx : Std.U32) (pk_seed : Slice Std.U8)
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(auth : Array (Array Std.U8 N) HP) (s : Nat) :
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∀ (start : Std.U32) (adrs : types.Adrs) (node : Array Std.U8 N),
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start.val + s < 2 ^ 32 →
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∀ (stop : Std.U32), stop.val = start.val + s →
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verify_mono.xmss_pk_from_sig_free_loop { start := start, «end» := stop }
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idx pk_seed adrs auth node
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= xmssFoldN idx pk_seed auth adrs node start s := by
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induction s with
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| zero =>
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intro start adrs node _ stop hstop
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have hse : start = stop := by apply Std.UScalar.eq_of_val_eq; omega
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subst hse
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unfold verify_mono.xmss_pk_from_sig_free_loop xmssFoldN
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rw [loop.eq_1]
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unfold verify_mono.xmss_pk_from_sig_free_loop.body core.iter.range.IteratorRange.next
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simp [core.cmp.impls.PartialOrdU32.lt]
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| succ k ih =>
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intro start adrs node hb stop hstop
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have hlt : start.val < stop.val := by omega
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have hb1 : start.val + 1 < 2 ^ 32 := by omega
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obtain ⟨w, hwok, hwv⟩ := u32_succ hb1
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rw [xmss_loop_step idx pk_seed auth start stop adrs node hlt hb1]
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unfold xmssFoldN
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rw [hwok]
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simp only [bind_tc_ok, bind_ok]
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have hbound : w.val + k < 2 ^ 32 := by omega
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have hstop' : stop.val = w.val + k := by omega
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apply bind_congr; intro adrs1
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apply bind_congr; intro i1
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apply bind_congr; intro i2
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by_cases hc : i2 = 0#u32
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· rw [if_pos hc, if_pos hc]
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apply bind_congr; rintro ⟨i3, adrs2⟩
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apply bind_congr; intro tmp
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apply bind_congr; intro adrs3
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apply bind_congr; intro s0
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apply bind_congr; intro i4
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apply bind_congr; intro a
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apply bind_congr; intro s1
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apply bind_congr; intro node1
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exact ih w adrs3 node1 hbound stop hstop'
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· rw [if_neg hc, if_neg hc]
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apply bind_congr; rintro ⟨i3, adrs2⟩
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apply bind_congr; intro i4
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apply bind_congr; intro tmp
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apply bind_congr; intro adrs3
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apply bind_congr; intro i5
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apply bind_congr; intro a
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apply bind_congr; intro s0
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apply bind_congr; intro s1
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apply bind_congr; intro node1
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exact ih w adrs3 node1 hbound stop hstop'
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end fips205
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