package noiseutil import ( "crypto/ecdh" "crypto/rand" "fmt" "io" "github.com/flynn/noise" ) // DHP256 is the NIST P-256 ECDH function var DHP256 noise.DHFunc = newNISTCurve("P256", ecdh.P256(), 32) type nistCurve struct { name string curve ecdh.Curve dhLen int pubLen int } func newNISTCurve(name string, curve ecdh.Curve, byteLen int) nistCurve { return nistCurve{ name: name, curve: curve, dhLen: byteLen, // Standard uncompressed format, type (1 byte) plus both coordinates pubLen: 1 + 2*byteLen, } } func (c nistCurve) GenerateKeypair(rng io.Reader) (noise.DHKey, error) { if rng == nil { rng = rand.Reader } privkey, err := c.curve.GenerateKey(rng) if err != nil { return noise.DHKey{}, err } pubkey := privkey.PublicKey() return noise.DHKey{Private: privkey.Bytes(), Public: pubkey.Bytes()}, nil } func (c nistCurve) DH(privkey, pubkey []byte) ([]byte, error) { ecdhPubKey, err := c.curve.NewPublicKey(pubkey) if err != nil { return nil, fmt.Errorf("unable to unmarshal pubkey: %w", err) } ecdhPrivKey, err := c.curve.NewPrivateKey(privkey) if err != nil { return nil, fmt.Errorf("unable to unmarshal private key: %w", err) } return ecdhPrivKey.ECDH(ecdhPubKey) } func (c nistCurve) DHLen() int { // NOTE: Noise Protocol specifies "DHLen" to represent two things: // - The size of the public key // - The return size of the DH() function // But for standard NIST ECDH, the sizes of these are different. // Luckily, the flynn/noise library actually only uses this DHLen() // value to represent the public key size, so that is what we are // returning here. The length of the DH() return bytes are unaffected by // this value here. return c.pubLen } func (c nistCurve) DHName() string { return c.name }