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expander: panic if requested output length overflows DST. #664

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Merged
bwesterb merged 1 commit into from
Jul 18, 2026
+19 −1
Merged

expander: panic if requested output length overflows DST. #664

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6 changes: 5 additions & 1 deletion expander/expander.go
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Original file line number Diff line number Diff line change
Expand Up @@ -95,8 +95,12 @@ func NewExpanderXOF(id xof.ID, kSecLevel uint, dst []byte) *expanderXOF {
return &expanderXOF{id, kSecLevel, dst}
}

// Expand panics if output's length is longer than 2^16 bytes.
// Expand panics if output's length exceeds 65535 bytes.
func (e *expanderXOF) Expand(in []byte, n uint) []byte {
if n >= 1<<16 {
panic(errorLongOutput)
}

bLen := []byte{0, 0}
binary.BigEndian.PutUint16(bLen, uint16(n))
pseudo := make([]byte, n)
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14 changes: 14 additions & 0 deletions expander/expander_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,20 @@ func TestExpander(t *testing.T) {
}
}

func TestXOFExpandLengthLimit(t *testing.T) {
exp := expander.NewExpanderXOF(xof.SHAKE128, 128, []byte("dst"))
if got := exp.Expand(nil, 1<<16-1); len(got) != 1<<16-1 {
t.Fatalf("unexpected output length: got %d, want %d", len(got), 1<<16-1)
}

defer func() {
if recover() == nil {
t.Fatal("Expand did not panic for an output length exceeding 65535 bytes")
}
}()
exp.Expand(nil, 1<<16)
}

func (vs *vectorExpanderSuite) testExpander(t *testing.T) {
var exp expander.Expander
switch vs.Hash {
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