// parseDSA parses DSA public key material from the given Reader. See RFC 4880,
// section 5.5.2.
func (pk *PublicKey) parseDSA(r io.Reader) (err error) {
	pk.p.bytes, pk.p.bitLength, err = readMPI(r)
	if err != nil {
		return
	}
	pk.q.bytes, pk.q.bitLength, err = readMPI(r)
	if err != nil {
		return
	}
	pk.g.bytes, pk.g.bitLength, err = readMPI(r)
	if err != nil {
		return
	}
	pk.y.bytes, pk.y.bitLength, err = readMPI(r)
	if err != nil {
		return
	}

	dsa := new(dsa.PublicKey)
	dsa.P = new(big.Int).SetBytes(pk.p.bytes)
	dsa.Q = new(big.Int).SetBytes(pk.q.bytes)
	dsa.G = new(big.Int).SetBytes(pk.g.bytes)
	dsa.Y = new(big.Int).SetBytes(pk.y.bytes)
	pk.PublicKey = dsa
	return
}