diff --git a/SoftU2FTool/SHA256.swift b/SoftU2FTool/SHA256.swift
index d1ba1b4..7dd60c1 100644
--- a/SoftU2FTool/SHA256.swift
+++ b/SoftU2FTool/SHA256.swift
@@ -41,7 +41,7 @@ class SHA256 {
         return SHA256(data: data).webSafeB64Digest
     }
 
-    let digest: Data
+    var digest: Data
 
     var tupleDigest: TupleDigest {
         return digest.withUnsafeBytes { digestPtr in