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keys: improve publick key checks with a check against P

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ANSI X9.62 says that if x or y coordinate are greater than or equal to
curve.Params().P, the conversion should return an error (see ANSI X9.62:2005
Section A.5.8 Step b, which invokes Section A.5.5, which does the check and
rejects when x or y are too big.

See https://github.com/golang/go/issues/20482 for more details.
This commit is contained in:
Roman Khimov 2019-09-05 12:31:03 +03:00
parent f12194f3b0
commit e537dc9ee4
1 changed files with 9 additions and 7 deletions
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16
pkg/crypto/keys/publickey.go
View file

@ -117,9 +117,6 @@ func decodeCompressedY(x *big.Int, ylsb uint) (*big.Int, error) {
y.Neg(y)
y.Mod(y, cp.P)
}
if !c.IsOnCurve(x, y) {
return nil, errors.New("compressed (x, ylsb) not on curve")
}
return y, nil
}
@ -145,6 +142,7 @@ func (p *PublicKey) DecodeBinary(r io.Reader) error {
switch prefix {
case 0x00:
// noop, initialized to nil
return nil
case 0x02, 0x03:
// Compressed public keys
xbytes := make([]byte, 32)
@ -166,15 +164,19 @@ func (p *PublicKey) DecodeBinary(r io.Reader) error {
if _, err = io.ReadFull(r, ybytes); err != nil {
return err
}
c := elliptic.P256()
x = new(big.Int).SetBytes(xbytes)
y = new(big.Int).SetBytes(ybytes)
if !c.IsOnCurve(x, y) {
return errors.New("point given is not on curve P256")
}
default:
return errors.Errorf("invalid prefix %d", prefix)
}
c := elliptic.P256()
cp := c.Params()
if !c.IsOnCurve(x, y) {
return errors.New("enccoded point is not on the P256 curve")
}
if x.Cmp(cp.P) >= 0 || y.Cmp(cp.P) >= 0 {
return errors.New("enccoded point is not correct (X or Y is bigger than P")
}
p.X, p.Y = x, y
return nil