Feature: add ssr support (#805)

* Refactor ssr stream cipher to expose iv and key

References:
https://github.com/Dreamacro/go-shadowsocks2
https://github.com/sh4d0wfiend/go-shadowsocksr2

* Implement ssr obfs

Reference:
https://github.com/mzz2017/shadowsocksR

* Implement ssr protocol

References:
https://github.com/mzz2017/shadowsocksR
https://github.com/shadowsocksRb/shadowsocksr-libev
https://github.com/shadowsocksr-backup/shadowsocksr

component/ssr/tools/encrypt.go

@@ -0,0 +1,33 @@
+package tools
+
+import (
+	"crypto/hmac"
+	"crypto/md5"
+	"crypto/sha1"
+)
+
+const HmacSHA1Len = 10
+
+func HmacMD5(key, data []byte) []byte {
+	hmacMD5 := hmac.New(md5.New, key)
+	hmacMD5.Write(data)
+	return hmacMD5.Sum(nil)[:16]
+}
+
+func HmacSHA1(key, data []byte) []byte {
+	hmacSHA1 := hmac.New(sha1.New, key)
+	hmacSHA1.Write(data)
+	return hmacSHA1.Sum(nil)[:20]
+}
+
+func MD5Sum(b []byte) []byte {
+	h := md5.New()
+	h.Write(b)
+	return h.Sum(nil)
+}
+
+func SHA1Sum(b []byte) []byte {
+	h := sha1.New()
+	h.Write(b)
+	return h.Sum(nil)
+}