add curve25519 key exchange

crypto/curve_25519.go

@@ -0,0 +1,45 @@
+package crypto
+
+import (
+	"crypto/rand"
+	"errors"
+
+	"golang.org/x/crypto/curve25519"
+)
+
+// KeyExchange manages the exchange of keys
+type curve25519KEX struct {
+	secret [32]byte
+	public [32]byte
+}
+
+var _ KeyExchange = &curve25519KEX{}
+
+// NewCurve25519KEX creates a new KeyExchange using Curve25519, see https://cr.yp.to/ecdh.html
+func NewCurve25519KEX() KeyExchange {
+	c := &curve25519KEX{}
+	if n, err := rand.Reader.Read(c.secret[:]); n != 32 || err != nil {
+		panic("Curve25519: could not create private key")
+	}
+	// See https://cr.yp.to/ecdh.html
+	c.secret[0] &= 248
+	c.secret[31] &= 127
+	c.secret[31] |= 64
+	curve25519.ScalarBaseMult(&c.public, &c.secret)
+	return c
+}
+
+func (c *curve25519KEX) PublicKey() []byte {
+	return c.public[:]
+}
+
+func (c *curve25519KEX) CalculateSharedKey(otherPublic []byte) ([]byte, error) {
+	if len(otherPublic) != 32 {
+		return nil, errors.New("Curve25519: expected public key of 32 byte")
+	}
+	var res [32]byte
+	var otherPublicArray [32]byte
+	copy(otherPublicArray[:], otherPublic)
+	curve25519.ScalarMult(&res, &c.secret, &otherPublicArray)
+	return res[:], nil
+}

crypto/curve_25519_test.go

@@ -0,0 +1,18 @@
+package crypto
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("ProofRsa", func() {
+	It("works", func() {
+		a := NewCurve25519KEX()
+		b := NewCurve25519KEX()
+		sA, err := a.CalculateSharedKey(b.PublicKey())
+		Expect(err).ToNot(HaveOccurred())
+		sB, err := b.CalculateSharedKey(a.PublicKey())
+		Expect(err).ToNot(HaveOccurred())
+		Expect(sA).To(Equal(sB))
+	})
+})

crypto/key_exchange.go

@@ -0,0 +1,7 @@
+package crypto
+
+// KeyExchange manages the exchange of keys
+type KeyExchange interface {
+	PublicKey() []byte
+	CalculateSharedKey(otherPublic []byte) ([]byte, error)
+}