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bls12381: Detects invalid prefix in G1 and G2 serialized elements #500

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Merged
merged 2 commits into from
Jun 10, 2024
Merged

bls12381: Detects invalid prefix in G1 and G2 serialized elements #500

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d556030
Test for invalid encodings of BLS12381.
armfazh Jun 10, 2024
5c44dde
Detects invalid encodings of bls12381 elements.
armfazh Jun 10, 2024
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56 changes: 37 additions & 19 deletions ecc/bls12381/doc.go
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Original file line number Diff line number Diff line change
Expand Up @@ -32,23 +32,41 @@
// is the lexicographically largest of the two associated with the encoded
// x-coordinate.
//
// |----------------------------------------------------|
// | Serialization Format |
// |-----|-------|-------|---------------|--------------|
// | MSB | MSB-1 | MSB-2 | Description | Encoding |
// |-----|-------|-------|---------------|--------------|
// | 0 | X | X | Uncompressed | e || x || y |
// | 1 | X | X | Compressed | e || x |
// |-----|-------|-------|---------------|--------------|
// | X | 0 | X | Non-Infinity | e || x || y |
// | X | 1 | X | Infinity | e || 0 || 0 |
// |-----|-------|-------|---------------|--------------|
// | | | | Compressed, | |
// | 1 | 0 | 1 | Non-Infinity, | e || x |
// | | | | Big y-coord | |
// |-----|-------|-------|---------------|--------------|
// | | | | Compressed, | |
// | 1 | 0 | 0 | Non-Infinity, | e || x |
// | | | | Small y-coord | |
// |----------------------------------------------------|
// |------------------------------------------------------|
// | Serialization Format |
// |-----|-------|-------|-----------------|--------------|
// | MSB | MSB-1 | MSB-2 | Description | Encoding |
// |-----|-------|-------|-----------------|--------------|
// | | | | Non-compressed, | |
// | 0 | 0 | 0 | Non-Infinity, | e || x || y |
// | | | | Zero. | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Non-compressed, | |
// | 0 | 0 | 1 | Non-Infinity, | Invalid |
// | | | | One. | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Non-compressed, | |
// | 0 | 1 | 0 | Infinity, | e || 0 || 0 |
// | | | | Zero. | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Non-compressed, | |
// | 0 | 1 | 1 | Infinity, | Invalid |
// | | | | One. | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Compressed, | |
// | 1 | 0 | 0 | Non-Infinity, | e || x |
// | | | | Small y-coord | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Compressed, | |
// | 1 | 0 | 1 | Non-Infinity, | e || x |
// | | | | Big y-coord | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Compressed, | |
// | 1 | 1 | 0 | Infinity, | e || 0 |
// | | | | Zero. | |
// |-----|-------|-------|-----------------|--------------|
// | | | | Compressed, | |
// | 1 | 1 | 1 | Infinity, | Invalid |
// | | | | One. | |
// |------------------------------------------------------|
package bls12381
8 changes: 7 additions & 1 deletion ecc/bls12381/g1.go
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Expand Up @@ -34,6 +34,12 @@ func (g *G1) SetBytes(b []byte) error {
return errInputLength
}

// Check for invalid prefixes
switch b[0] & 0xE0 {
case 0x20, 0x60, 0xE0:
return errEncoding
}

isCompressed := int((b[0] >> 7) & 0x1)
isInfinity := int((b[0] >> 6) & 0x1)
isBigYCoord := int((b[0] >> 5) & 0x1)
Expand All @@ -44,7 +50,7 @@ func (g *G1) SetBytes(b []byte) error {
l = G1SizeCompressed
}
zeros := make([]byte, l-1)
if (b[0]&0x1F) != 0 || subtle.ConstantTimeCompare(b[1:], zeros) != 1 {
if (b[0]&0x1F) != 0 || subtle.ConstantTimeCompare(b[1:l], zeros) != 1 {
return errEncoding
}
g.SetIdentity()
Expand Down
7 changes: 7 additions & 0 deletions ecc/bls12381/g1_test.go
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Expand Up @@ -143,6 +143,13 @@ func TestG1Serial(t *testing.T) {
want = *randomG1(t)
}
})
t.Run("badPrefix", func(t *testing.T) {
q := new(G1)
b := make([]byte, G1Size)
for _, b[0] = range []byte{0x20, 0x60, 0xE0} {
test.CheckIsErr(t, q.SetBytes(b), mustErr)
}
})
t.Run("badLength", func(t *testing.T) {
q := new(G1)
p := randomG1(t)
Expand Down
8 changes: 7 additions & 1 deletion ecc/bls12381/g2.go
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Expand Up @@ -32,6 +32,12 @@ func (g *G2) SetBytes(b []byte) error {
return errInputLength
}

// Check for invalid prefixes
switch b[0] & 0xE0 {
case 0x20, 0x60, 0xE0:
return errEncoding
}

isCompressed := int((b[0] >> 7) & 0x1)
isInfinity := int((b[0] >> 6) & 0x1)
isBigYCoord := int((b[0] >> 5) & 0x1)
Expand All @@ -42,7 +48,7 @@ func (g *G2) SetBytes(b []byte) error {
l = G2SizeCompressed
}
zeros := make([]byte, l-1)
if (b[0]&0x1F) != 0 || subtle.ConstantTimeCompare(b[1:], zeros) != 1 {
if (b[0]&0x1F) != 0 || subtle.ConstantTimeCompare(b[1:l], zeros) != 1 {
return errEncoding
}
g.SetIdentity()
Expand Down
7 changes: 7 additions & 0 deletions ecc/bls12381/g2_test.go
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Expand Up @@ -102,6 +102,13 @@ func TestG2Serial(t *testing.T) {
want = *randomG2(t)
}
})
t.Run("badPrefix", func(t *testing.T) {
q := new(G2)
b := make([]byte, G2Size)
for _, b[0] = range []byte{0x20, 0x60, 0xE0} {
test.CheckIsErr(t, q.SetBytes(b), mustErr)
}
})
t.Run("badLength", func(t *testing.T) {
q := new(G2)
p := randomG2(t)
Expand Down
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