From de5b1817c782f0f3459a8b7b257d576e6fc5d22c Mon Sep 17 00:00:00 2001
From: Kyle <kyle@tyrfingr.is>
Date: Fri, 10 Jan 2014 16:27:14 -0700
Subject: [PATCH] SHA256 the ECDH shared key

This ensures the shared key is a more uniform distribution than just
taking the bytes from the shared X.
---
 ecdh/ecdh.go | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ecdh/ecdh.go b/ecdh/ecdh.go
index b05d6da..5b2c06c 100644
--- a/ecdh/ecdh.go
+++ b/ecdh/ecdh.go
@@ -11,6 +11,7 @@ import (
 	"crypto/hmac"
 	"crypto/rand"
 	"crypto/sha1"
+	"crypto/sha256"
 	"errors"
 	"github.com/cloudflare/redoctober/padding"
 	"github.com/cloudflare/redoctober/symcrypt"
@@ -36,7 +37,7 @@ func Encrypt(pub ecdsa.PublicKey, in []byte) (out []byte, err error) {
 	if x == nil {
 		return nil, errors.New("Failed to generate encryption key")
 	}
-	shared := x.Bytes()
+	shared := sha256.Sum256(x.Bytes())
 	iv, err := symcrypt.MakeRandom(16)
 	if err != nil {
 		return
@@ -82,7 +83,7 @@ func Decrypt(priv *ecdsa.PrivateKey, in []byte) (out []byte, err error) {
 	if x == nil {
 		return nil, errors.New("Failed to generate encryption key")
 	}
-	shared := x.Bytes()
+	shared := sha256.Sum256(x.Bytes())
 
 	tagStart := len(ct) - sha1.Size
 	h := hmac.New(sha1.New, shared[16:])