Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

fix(arith): bug in vartime inversion when using fused inverse+multiply by factor - found by Guido Vranken #433

Merged
merged 1 commit into from
Jul 16, 2024
+29 −2
Merged

fix(arith): bug in vartime inversion when using fused inverse+multiply by factor - found by Guido Vranken #433

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions constantine/math/arithmetic/limbs_exgcd.nim
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -854,7 +854,7 @@ func invmod_vartime*(
r.setZero()
return
if a.isOne().bool:
r.setOne()
r = F
return

const Excess = 2
Expand Down Expand Up @@ -888,7 +888,7 @@ func invmod_vartime*(
r.setZero()
return
if a.isOne().bool:
r.setOne()
r = F
return

const Excess = 2
Expand Down
17 changes: 17 additions & 0 deletions tests/math_bigints/t_bigints.nim
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ import
# Standard library
std/unittest,
# Internal
constantine/named/algebras,
constantine/math/io/io_bigints,
constantine/math/arithmetic,
constantine/platforms/abstractions,
Expand Down Expand Up @@ -658,6 +659,22 @@ proc mainModularInverse() =
bool(r == expected)
bool(r2 == expected)

test "#433 - CryptoFuzz / Oss-Fuzz bug with unit inversion":
block:
let a = BigInt[255].fromUint(1'u)
let M = BLS12_381.scalarFieldModulus()
let F = Fr[BLS12_381].getR2modP()

var r = canary(BigInt[255])
var r2 = canary(BigInt[255])

r.invmod(a, F, M)
r2.invmod_vartime(a, F, M)

check:
bool(r == F)
bool(r2 == F)

mainArith()
mainMul()
mainMulHigh()
Expand Down
10 changes: 10 additions & 0 deletions tests/math_fields/t_finite_fields_powinv.nim
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -465,4 +465,14 @@ proc main_anti_regression =

check: bool(a == expected)

suite "Bug highlighted by 24/7 fuzzing (Guido Vranken's CryptoFuzz / Google-OssFuzz)" & " [" & $WordBitWidth & "-bit words]":
test "#433 - Short-circuit when Montgomery a' = aR (mod p) == 1":
let a = BigInt[255].fromDecimal("12549076656233958353659347336803947287922716146853412054870763148006372261952")
let expected = BigInt[255].fromDecimal("10920338887063814464675503992315976177888879664585288394250266608035967270910")
var aa = Fr[BLS12_381].fromBig(a)

doAssert bool(aa.mres.isOne())
aa.inv_vartime()
check: bool(aa.toBig() == expected)

main_anti_regression()
Loading