vendor: pull in missing go-echd library

vendor/github.com/wsddn/go-ecdh/LICENSE

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+Copyright (c) 2014, tang0th
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+    * Neither the name of tang0th nor the names of its contributors may be
+      used to endorse or promote products derived from this software without
+      specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 

vendor/github.com/wsddn/go-ecdh/Readme.md

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+# ECDH
+
+[![Build Status](https://travis-ci.org/wsddn/go-ecdh.svg?branch=master)](https://travis-ci.org/wsddn/go-ecdh)
+
+This is a go implementation of elliptical curve diffie-hellman key exchange method.
+It supports the NIST curves (and any curves using the `elliptic.Curve` go interface)
+as well as djb's curve25519. 
+
+The library handles generating of keys, generating a shared secret, and the
+(un)marshalling of the elliptical curve keys into slices of bytes.
+
+## Warning and Disclaimer
+I am not a cryptographer, this was written as part of a personal project to learn about cryptographic systems and protocols. No claims as to the security of this library are made, I would not advise using it for anything that requires any level of security. Pull requests or issues about security flaws are however still welcome.
+
+## Compatibility
+Works with go 1.2 onwards.
+
+## TODO
+ * Improve documentation

vendor/github.com/wsddn/go-ecdh/curve25519.go

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+package ecdh
+
+import (
+	"crypto"
+	"io"
+
+	"golang.org/x/crypto/curve25519"
+)
+
+type curve25519ECDH struct {
+	ECDH
+}
+
+// NewCurve25519ECDH creates a new ECDH instance that uses djb's curve25519
+// elliptical curve.
+func NewCurve25519ECDH() ECDH {
+	return &curve25519ECDH{}
+}
+
+func (e *curve25519ECDH) GenerateKey(rand io.Reader) (crypto.PrivateKey, crypto.PublicKey, error) {
+	var pub, priv [32]byte
+	var err error
+
+	_, err = io.ReadFull(rand, priv[:])
+	if err != nil {
+		return nil, nil, err
+	}
+
+	priv[0] &= 248
+	priv[31] &= 127
+	priv[31] |= 64
+
+	curve25519.ScalarBaseMult(&pub, &priv)
+
+	return &priv, &pub, nil
+}
+
+func (e *curve25519ECDH) Marshal(p crypto.PublicKey) []byte {
+	pub := p.(*[32]byte)
+	return pub[:]
+}
+
+func (e *curve25519ECDH) Unmarshal(data []byte) (crypto.PublicKey, bool) {
+	var pub [32]byte
+	if len(data) != 32 {
+		return nil, false
+	}
+
+	copy(pub[:], data)
+	return &pub, true
+}
+
+func (e *curve25519ECDH) GenerateSharedSecret(privKey crypto.PrivateKey, pubKey crypto.PublicKey) ([]byte, error) {
+	var priv, pub, secret *[32]byte
+
+	priv = privKey.(*[32]byte)
+	pub = pubKey.(*[32]byte)
+	secret = new([32]byte)
+
+	curve25519.ScalarMult(secret, priv, pub)
+	return secret[:], nil
+}

vendor/github.com/wsddn/go-ecdh/ecdh.go

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+package ecdh
+
+import (
+	"crypto"
+	"io"
+)
+
+// The main interface for ECDH key exchange.
+type ECDH interface {
+	GenerateKey(io.Reader) (crypto.PrivateKey, crypto.PublicKey, error)
+	Marshal(crypto.PublicKey) []byte
+	Unmarshal([]byte) (crypto.PublicKey, bool)
+	GenerateSharedSecret(crypto.PrivateKey, crypto.PublicKey) ([]byte, error)
+}

vendor/github.com/wsddn/go-ecdh/elliptic.go

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+package ecdh
+
+import (
+	"crypto"
+	"crypto/elliptic"
+	"io"
+	"math/big"
+)
+
+type ellipticECDH struct {
+	ECDH
+	curve elliptic.Curve
+}
+
+type ellipticPublicKey struct {
+	elliptic.Curve
+	X, Y *big.Int
+}
+
+type ellipticPrivateKey struct {
+	D []byte
+}
+
+// NewEllipticECDH creates a new instance of ECDH with the given elliptic.Curve curve
+// to use as the elliptical curve for elliptical curve diffie-hellman.
+func NewEllipticECDH(curve elliptic.Curve) ECDH {
+	return &ellipticECDH{
+		curve: curve,
+	}
+}
+
+func (e *ellipticECDH) GenerateKey(rand io.Reader) (crypto.PrivateKey, crypto.PublicKey, error) {
+	var d []byte
+	var x, y *big.Int
+	var priv *ellipticPrivateKey
+	var pub *ellipticPublicKey
+	var err error
+
+	d, x, y, err = elliptic.GenerateKey(e.curve, rand)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	priv = &ellipticPrivateKey{
+		D: d,
+	}
+	pub = &ellipticPublicKey{
+		Curve: e.curve,
+		X: x,
+		Y: y,
+	}
+	
+	return priv, pub, nil
+}
+
+func (e *ellipticECDH) Marshal(p crypto.PublicKey) []byte {
+	pub := p.(*ellipticPublicKey)
+	return elliptic.Marshal(e.curve, pub.X, pub.Y)
+}
+
+func (e *ellipticECDH) Unmarshal(data []byte) (crypto.PublicKey, bool) {
+	var key *ellipticPublicKey
+	var x, y *big.Int
+
+	x, y = elliptic.Unmarshal(e.curve, data)
+	if x == nil || y == nil {
+		return key, false
+	}
+	key = &ellipticPublicKey{
+		Curve: e.curve,
+		X:     x,
+		Y:     y,
+	}
+	return key, true
+}
+
+// GenerateSharedSecret takes in a public key and a private key
+// and generates a shared secret.
+//
+// RFC5903 Section 9 states we should only return x.
+func (e *ellipticECDH) GenerateSharedSecret(privKey crypto.PrivateKey, pubKey crypto.PublicKey) ([]byte, error) {
+	priv := privKey.(*ellipticPrivateKey)
+	pub := pubKey.(*ellipticPublicKey)
+
+	x, _ := e.curve.ScalarMult(pub.X, pub.Y, priv.D)
+	return x.Bytes(), nil
+}