diff --git a/.drone.starlark b/.drone.starlark
index 08c6c56..aa53a5f 100644
--- a/.drone.starlark
+++ b/.drone.starlark
@@ -5,11 +5,21 @@ def main(ctx):
 		"type": "docker",
 		"name": "testing",
 		"steps": [
+			{
+				"name": "update submodules",
+				"image": "docker.io/immawanderer/fedora-cpp:linux-amd64",
+				"pull": "always",
+				"depends_on": ["clone"],
+				"commands": [
+					"uname -r",
+					"git submodule update --init --recursive"
+				]
+			},
 			{
 				"name": "cppcheck",
 				"image": "docker.io/archlinux:base-devel",
 				"pull": "always",
-				"depends_on": ["clone"],
+				"depends_on": ["update submodules"],
 				"commands": [
 					"pacman -Sy cppcheck --noconfirm --needed",
 					"uname -r",
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..2e5371e
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "lib/fmt"]
+	path = lib/fmt
+	url = https://github.com/fmtlib/fmt.git
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f4ef6a9..5ece0fc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,6 +4,23 @@ project(fortuna LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+find_package(Git QUIET)
+if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
+  option(GIT_SUBMODULE "Check submodules during build" ON)
+  if(GIT_SUBMODULE)
+    message(STATUS "Update submodule(s)")
+    message(STATUS "Current source dir: ${CMAKE_CURRENT_SOURCE_DIR}")
+    execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive
+                    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+                    RESULT_VARIABLE GIT_SUBMOD_RESULT)
+    if(NOT GIT_SUBMOD_RESULT EQUAL "0")
+      message(FATAL_ERROR "git submodule update --init --recursive failed with ${GIT_SUBMOD_RESULT}, please checkout submodules")
+    endif()
+  endif()
+endif()
+
+add_subdirectory(lib/fmt EXCLUDE_FROM_ALL)
+
   if(CMAKE_BUILD_TYPE MATCHES "Debug")
     # Produce debugging information in the operating system's native format.
     # Level 3 includes extra information, such as all the macro definitions
@@ -99,4 +116,7 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
   endif()
 
 add_executable(fortuna main.cpp generator.cpp generator.h fortuna.cpp fortuna.h)
-target_link_libraries(fortuna cryptopp)
+# ref: https://cmake.org/pipermail/cmake/2016-May/063400.html
+target_link_libraries(fortuna
+    PRIVATE cryptopp
+    PRIVATE fmt::fmt-header-only)
diff --git a/fortuna.cpp b/fortuna.cpp
index 8501348..915a438 100644
--- a/fortuna.cpp
+++ b/fortuna.cpp
@@ -9,10 +9,10 @@
 #include <cryptopp/filters.h>
 #include <cryptopp/serpent.h>
 #include <cryptopp/ccm.h>
+#include <fmt/core.h>
 
 #include <cassert>
 #include <cstring>
-#include <iostream>
 
 
 namespace fortuna {
@@ -46,7 +46,7 @@ namespace fortuna {
 		std::string cipher, encoded_c, decrypted;
 
 		try {
-			std::cout << "plain text: " << plain << std::endl;
+			fmt::print("plain text: {}\n", plain);
 
 			CTR_Mode<Serpent>::Encryption e;
 			e.SetKeyWithIV(key,key.size(),ctr);
@@ -63,7 +63,7 @@ namespace fortuna {
 			); // StringSource
 		}
 		catch(CryptoPP::Exception& e) {
-			std::cerr << e.what() << std::endl;
+			fmt::print(stderr, "{}\n", e.what());
 			exit(1);
 		}
 
@@ -73,7 +73,7 @@ namespace fortuna {
 				new StringSink(encoded_c)
 			) // HexEncoder
 		); // StringSource
-		std::cout << "cipher text: " << encoded_c << std::endl;
+		fmt::print("cipher text: {}\n", encoded_c);
 
 		try {
 			CTR_Mode<Serpent>::Decryption d;
@@ -86,10 +86,10 @@ namespace fortuna {
 				) // StreamTransformationFilter
 			); // StringSource
 
-			std::cout << "decrypted text: " << decrypted << std::endl;
+			fmt::print("decrypted text: {}\n", decrypted);
 		}
 		catch(CryptoPP::Exception& e) {
-			std::cerr << e.what() << std::endl;
+			fmt::print(stderr, "{}\n", e.what());
 			exit(1);
 		}
 
diff --git a/generator.cpp b/generator.cpp
index 4e1ca0b..aba46ca 100644
--- a/generator.cpp
+++ b/generator.cpp
@@ -5,11 +5,11 @@
 #include <cassert>
 #include <cstdint>
 #include <stdexcept>
-#include <iostream>
 
 #include <cryptopp/hex.h>
 #include <cryptopp/filters.h>
 #include <cryptopp/sha3.h>
+#include <fmt/core.h>
 
 #include "generator.h"
 
@@ -69,7 +69,7 @@ auto Generator::do_sha(const std::string& k_n_s) -> std::string {
 		new HashFilter(sha3_256,new HexEncoder(new StringSink(digest),false))
 	);
 	assert(digest == to_compare);
-	std::cout << digest << std::endl;
+	fmt::print("{}\n", digest);
 	digest.erase();
 
 	// return digest;
diff --git a/lib/fmt b/lib/fmt
new file mode 160000
index 0000000..c089f7d
--- /dev/null
+++ b/lib/fmt
@@ -0,0 +1 @@
+Subproject commit c089f7d497bcce35a0fd6da0512f8585ed1cc002
diff --git a/main.cpp b/main.cpp
index 6928e08..54dd29a 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,11 +1,10 @@
-#include <iostream>
 #include "fortuna.h"
 #include "generator.h"
 
+#include <fmt/core.h>
+
 int main() {
-	using std::cout;
-	using std::endl;
-	cout << "[*] doing evil stuff" << endl;
+	fmt::print("[*] doing evil stuff\n");
 	fortuna::Fortuna f;
 	f.random_data(4);
 	return 0;