def mask_okb

bend-collections-laws-crypto@1.0.0.0 · proofs/crypto/curve25519/xbits.bend:244

import Base
import bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend as F
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend as N
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend as L
import bend-collections-laws-crypto@1.0.0.0/proofs/math/hash/hash.bend as HH
import bend-collections-laws-crypto@1.0.0.0/proofs/crypto/curve25519/limbs.bend as LM

244def mask_okb(+n: Nat, +xs: List<&2, U32>, +e: {LM.okb(1n+n, xs, 255n) == True{} : Bool}) -> {LM.okb(1n+n, F.mask_top(xs), 255n) == True{} : Bool}:
245  match n xs:
246    case _ Nil{}:
247      Empty.absurd({LM.okb(1n+n, Nil{}, 255n) == True{} : Bool}, L.false_true(e))
248    case 0n Con{+x, Nil{}}:
249      L.and_intro(Nat.is_le(v(U32.and(x, 127)), 255n), True{}, N.le_trans(v(U32.and(x, 127)), 127n, 255n, HH.and_le32(x, 127), {==}), {==})
250    case 0n Con{x, Con{y, yt}}:
251      Empty.absurd({LM.okb(1n, F.mask_top(Con{x, Con{y, yt}}), 255n) == True{} : Bool}, L.false_true(LM.okb_tail(0n, x, Con{y, yt}, 255n, e)))
252    case 1n+m Con{x, Nil{}}:
253      Empty.absurd({LM.okb(2n+m, F.mask_top(Con{x, Nil{}}), 255n) == True{} : Bool}, L.false_true(LM.okb_tail(1n+m, x, Nil{}, 255n, e)))
254    case 1n+ +m Con{+x, Con{+y, +yt}}:
255      L.and_intro(Nat.is_le(v(x), 255n), LM.okb(1n+m, F.mask_top(Con{y, yt}), 255n), LM.okb_head(1n+m, x, Con{y, yt}, 255n, e), mask_okb(m, Con{y, yt}, LM.okb_tail(1n+m, x, Con{y, yt}, 255n, e)))