diff --git a/util.h b/util.h
index d7ec2bb..7c9a044 100644
--- a/util.h
+++ b/util.h
@@ -16,6 +16,19 @@ class Util final {
 public:
 	static constexpr const std::size_t gen_block_size{32}; // 256 bits
 
+	static auto de_hex(const std::string& str) -> const std::string {
+		std::string s{str};
+		std::string dst;
+		CryptoPP::HexDecoder decoder;
+
+		decoder.Put(reinterpret_cast<CryptoPP::byte*>(s.data()), s.size());
+		decoder.MessageEnd();
+		dst.resize(gen_block_size);
+		decoder.Get(reinterpret_cast<CryptoPP::byte*>(&dst[0]), dst.size());
+
+		return dst;
+	}
+
 	static auto do_sha(const std::string& str_to_hash) -> const std::string {
 		// do sha256
 		std::string digest;