diff --git a/ec/id.go b/ec/id.go
index 01db18b..4fbaca3 100644
--- a/ec/id.go
+++ b/ec/id.go
@@ -1,10 +1,38 @@
 package ec
 
-import "encoding/base64"
+import (
+	"encoding/base64"
+	"errors"
+	"reflect"
+	"unsafe"
+)
 
 // ID 唯一ID（160位）
 type ID [20]byte
 
 func (id ID) String() string {
+	return EncodeIDToString(id)
+}
+
+var EncodeIDToString = func(id ID) string {
 	return base64.RawURLEncoding.EncodeToString(id[:])
 }
+
+var DecodeStringToID = func(str string) (id ID, err error) {
+	if base64.RawURLEncoding.DecodedLen(len(str)) > len(id) {
+		err = errors.New("string too long")
+		return
+	}
+	base64.RawURLEncoding.Decode(id[:], string2Bytes(str))
+	return
+}
+
+func string2Bytes(s string) []byte {
+	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	bh := reflect.SliceHeader{
+		Data: sh.Data,
+		Len:  sh.Len,
+		Cap:  sh.Len,
+	}
+	return *(*[]byte)(unsafe.Pointer(&bh))
+}