func unmarshalECC()

in certtostore_windows.go [1302:1341]

• 32 lines of code
• 8 McCabe index (conditional complexity)

func unmarshalECC(buf []byte, kh uintptr) (*ecdsa.PublicKey, error) {
	// BCRYPT_ECCKEY_BLOB from bcrypt.h
	header := struct {
		Magic uint32
		Key   uint32
	}{}

	r := bytes.NewReader(buf)
	if err := binary.Read(r, binary.LittleEndian, &header); err != nil {
		return nil, err
	}

	curve, ok := curveIDs[header.Magic]
	if !ok {
		// Fix for b/185945636, where despite specifying the curve, nCrypt returns
		// an incorrect response with BCRYPT_ECDSA_PUBLIC_GENERIC_MAGIC.
		var err error
		curve, err = curveName(kh)
		if err != nil {
			return nil, fmt.Errorf("unsupported header magic: %x and cannot match the curve by name: %v", header.Magic, err)
		}
	}

	keyX := make([]byte, header.Key)
	if n, err := r.Read(keyX); n != int(header.Key) || err != nil {
		return nil, fmt.Errorf("failed to read key X (%d, %v)", n, err)
	}

	keyY := make([]byte, header.Key)
	if n, err := r.Read(keyY); n != int(header.Key) || err != nil {
		return nil, fmt.Errorf("failed to read key Y (%d, %v)", n, err)
	}

	pub := &ecdsa.PublicKey{
		Curve: curve,
		X:     new(big.Int).SetBytes(keyX),
		Y:     new(big.Int).SetBytes(keyY),
	}
	return pub, nil
}