diff --git a/unit-tests/CMakeLists.txt b/unit-tests/CMakeLists.txt
new file mode 100644
index 0000000..7e64b05
--- /dev/null
+++ b/unit-tests/CMakeLists.txt
@@ -0,0 +1,62 @@
+cmake_minimum_required(VERSION 3.10)
+
+if(${CMAKE_VERSION} VERSION_LESS 3.10)
+    cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+endif()
+
+# project information
+project(unit_tests
+        VERSION 0.1
+	      DESCRIPTION "Unit tests for Ledger OpenPGP application"
+        LANGUAGES C)
+
+
+# guard against bad build-type strings
+if (NOT CMAKE_BUILD_TYPE)
+  set(CMAKE_BUILD_TYPE "Release")
+endif()
+
+# guard against in-source builds
+if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
+  message(FATAL_ERROR "In-source builds not allowed. Please make a new directory (called a build directory) and run CMake from there. You may need to remove CMakeCache.txt. ")
+endif()
+
+include(CTest)
+
+# specify C standard
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD_REQUIRED True)
+
+add_compile_options(-Wall -Wextra -g -pedantic --coverage)
+# Flag depending on the Build Type
+set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -O0")
+set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}-O3")
+
+set(GCC_COVERAGE_LINK_FLAGS "--coverage -lgcov")
+set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")
+set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")
+
+set(APP_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../src")
+set(SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/src")
+set(MOCK_DIR "${CMAKE_CURRENT_SOURCE_DIR}/mocks")
+
+add_compile_definitions(TEST)
+
+include_directories(
+  ${MOCK_DIR}
+  ${APP_DIR}
+)
+# include_directories($ENV{BOLOS_SDK}/lib_standard_app)
+
+add_executable(test_io
+    ${SRC_DIR}/test_io.c
+    ${MOCK_DIR}/mocks.c
+    ${APP_DIR}/gpg_io.c
+    ${APP_DIR}/gpg_vars.c
+)
+
+target_link_libraries(test_io PUBLIC
+                      cmocka
+                      gcov)
+
+add_test(test_io test_io)
diff --git a/unit-tests/README.md b/unit-tests/README.md
new file mode 100644
index 0000000..133fad0
--- /dev/null
+++ b/unit-tests/README.md
@@ -0,0 +1,48 @@
+# Unit tests
+
+## Prerequisite
+
+Be sure to have installed:
+
+- CMake >= 3.10
+- CMocka >= 1.1.5
+
+and for code coverage generation:
+
+- lcov >= 1.14
+
+## Overview
+
+In `unit-tests` folder, compile with:
+
+```shell
+cmake -Bbuild -H. && make -C build
+```
+
+and run tests with:
+
+```shell
+CTEST_OUTPUT_ON_FAILURE=1 make -C build test
+```
+
+To get more verbose output, use:
+
+```shell
+CTEST_OUTPUT_ON_FAILURE=1 make -C build test ARGS="-V"
+```
+
+Or also directly with:
+
+```shell
+CTEST_OUTPUT_ON_FAILURE=1 build/test_io
+```
+
+## Generate code coverage
+
+Just execute in `unit-tests` folder:
+
+```shell
+./gen_coverage.sh
+```
+
+it will output `coverage.total` and `coverage/` folder with HTML details (in `coverage/index.html`).
diff --git a/unit-tests/gen_coverage.sh b/unit-tests/gen_coverage.sh
new file mode 100755
index 0000000..8048270
--- /dev/null
+++ b/unit-tests/gen_coverage.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -x
+set -e
+
+BUILD_DIRECTORY=$(realpath build/)
+
+lcov --directory . -b "${BUILD_DIRECTORY}" --capture --initial -o coverage.base &&
+lcov --rc lcov_branch_coverage=1 --directory . -b "${BUILD_DIRECTORY}" --capture -o coverage.capture &&
+lcov --directory . -b "${BUILD_DIRECTORY}" --add-tracefile coverage.base --add-tracefile coverage.capture -o coverage.info &&
+lcov --directory . -b "${BUILD_DIRECTORY}" --remove coverage.info '*/unit-tests/*' -o coverage.info &&
+echo "Generated 'coverage.info'." &&
+genhtml coverage.info -o coverage
+
+rm -f coverage.base coverage.capture
diff --git a/unit-tests/mocks/bolos_target.h b/unit-tests/mocks/bolos_target.h
new file mode 100644
index 0000000..e69de29
diff --git a/unit-tests/mocks/cx.h b/unit-tests/mocks/cx.h
new file mode 100644
index 0000000..b475a99
--- /dev/null
+++ b/unit-tests/mocks/cx.h
@@ -0,0 +1,30 @@
+
+
+#define cx_rsa_public_key_t      char
+#define cx_rsa_1024_public_key_t char
+#define cx_rsa_2048_public_key_t char
+#define cx_rsa_3072_public_key_t char
+#define cx_rsa_4096_public_key_t char
+
+#define cx_rsa_private_key_t      char
+#define cx_rsa_1024_private_key_t char
+#define cx_rsa_2048_private_key_t char
+#define cx_rsa_3072_private_key_t char
+#define cx_rsa_4096_private_key_t char
+
+#define cx_ecfp_public_key_t     char
+#define cx_ecfp_256_public_key_t char
+#define cx_ecfp_384_public_key_t char
+#define cx_ecfp_512_public_key_t char
+#define cx_ecfp_640_public_key_t char
+
+#define cx_ecfp_private_key_t     char
+#define cx_ecfp_256_private_key_t char
+#define cx_ecfp_384_private_key_t char
+#define cx_ecfp_512_private_key_t char
+#define cx_ecfp_640_private_key_t char
+
+#define cx_sha3_t   char
+#define cx_sha256_t char
+
+#define cx_aes_key_t char
diff --git a/unit-tests/mocks/lcx_sha3.h b/unit-tests/mocks/lcx_sha3.h
new file mode 100644
index 0000000..e69de29
diff --git a/unit-tests/mocks/ledger_assert.h b/unit-tests/mocks/ledger_assert.h
new file mode 100644
index 0000000..90e97d4
--- /dev/null
+++ b/unit-tests/mocks/ledger_assert.h
@@ -0,0 +1,6 @@
+#define LEDGER_ASSERT(test, message) \
+    do {                             \
+        if (!(test)) {               \
+            return;                  \
+        }                            \
+    } while (0)
diff --git a/unit-tests/mocks/mocks.c b/unit-tests/mocks/mocks.c
new file mode 100644
index 0000000..ebb703d
--- /dev/null
+++ b/unit-tests/mocks/mocks.c
@@ -0,0 +1,17 @@
+
+#include "os.h"
+
+unsigned char G_io_apdu_buffer[IO_APDU_BUFFER_SIZE];
+
+unsigned short io_exchange(unsigned char channel_and_flags, unsigned short tx_len) {
+    (void) channel_and_flags;
+    (void) tx_len;
+    return 0;
+}
+
+void nvm_write(void *dst_adr, void *src_adr, unsigned int src_len) {
+    (void) dst_adr;
+    (void) src_adr;
+    (void) src_len;
+    return;
+}
diff --git a/unit-tests/mocks/offsets.h b/unit-tests/mocks/offsets.h
new file mode 100644
index 0000000..3db4bc1
--- /dev/null
+++ b/unit-tests/mocks/offsets.h
@@ -0,0 +1,26 @@
+#pragma once
+
+/**
+ * Offset of instruction class.
+ */
+#define OFFSET_CLA 0
+/**
+ * Offset of instruction code.
+ */
+#define OFFSET_INS 1
+/**
+ * Offset of instruction parameter 1.
+ */
+#define OFFSET_P1 2
+/**
+ * Offset of instruction parameter 2.
+ */
+#define OFFSET_P2 3
+/**
+ * Offset of command data length.
+ */
+#define OFFSET_LC 4
+/**
+ * Offset of command data.
+ */
+#define OFFSET_CDATA 5
diff --git a/unit-tests/mocks/os.h b/unit-tests/mocks/os.h
new file mode 100644
index 0000000..a6c7cad
--- /dev/null
+++ b/unit-tests/mocks/os.h
@@ -0,0 +1,22 @@
+
+#include <stdint.h>
+#include <string.h>
+
+#undef MAX
+#define MAX(a, b) (((a) > (b)) ? (a) : (b))
+
+#define PRINTF(...)
+#define THROW(x)
+
+// send tx_len bytes (atr or rapdu) and retrieve the length of the next command apdu (over the
+// requested channel)
+#define CHANNEL_APDU       0
+#define IO_RETURN_AFTER_TX 0x20
+#define IO_ASYNCH_REPLY    0x10  // avoid apdu state reset if tx_len == 0 when we're expected to reply
+
+#define IO_APDU_BUFFER_SIZE (255 + 5 + 64)
+
+extern unsigned char G_io_apdu_buffer[IO_APDU_BUFFER_SIZE];
+
+extern unsigned short io_exchange(unsigned char channel_and_flags, unsigned short tx_len);
+extern void nvm_write(void *dst_adr, void *src_adr, unsigned int src_len);
diff --git a/unit-tests/mocks/os_utils.h b/unit-tests/mocks/os_utils.h
new file mode 100644
index 0000000..510f2ef
--- /dev/null
+++ b/unit-tests/mocks/os_utils.h
@@ -0,0 +1,23 @@
+#pragma once
+
+#define U2(hi, lo) ((((hi) &0xFFu) << 8) | ((lo) &0xFFu))
+#define U4(hi3, hi2, lo1, lo0) \
+    ((((hi3) &0xFFu) << 24) | (((hi2) &0xFFu) << 16) | (((lo1) &0xFFu) << 8) | ((lo0) &0xFFu))
+static inline uint16_t U2BE(const uint8_t *buf, size_t off) {
+    return (buf[off] << 8) | buf[off + 1];
+}
+static inline uint32_t U4BE(const uint8_t *buf, size_t off) {
+    return (((uint32_t) buf[off]) << 24) | (buf[off + 1] << 16) | (buf[off + 2] << 8) |
+           buf[off + 3];
+}
+
+static inline void U2BE_ENCODE(uint8_t *buf, size_t off, uint32_t value) {
+    buf[off + 0] = (value >> 8) & 0xFF;
+    buf[off + 1] = value & 0xFF;
+}
+static inline void U4BE_ENCODE(uint8_t *buf, size_t off, uint32_t value) {
+    buf[off + 0] = (value >> 24) & 0xFF;
+    buf[off + 1] = (value >> 16) & 0xFF;
+    buf[off + 2] = (value >> 8) & 0xFF;
+    buf[off + 3] = value & 0xFF;
+}
diff --git a/unit-tests/mocks/usbd_ccid_if.h b/unit-tests/mocks/usbd_ccid_if.h
new file mode 100644
index 0000000..37dc501
--- /dev/null
+++ b/unit-tests/mocks/usbd_ccid_if.h
@@ -0,0 +1 @@
+#define PIN_OPR_APDU_CLA 0xEF
diff --git a/unit-tests/mocks/ux.h b/unit-tests/mocks/ux.h
new file mode 100644
index 0000000..7256169
--- /dev/null
+++ b/unit-tests/mocks/ux.h
@@ -0,0 +1 @@
+#define ux_state_t char
diff --git a/unit-tests/src/test_io.c b/unit-tests/src/test_io.c
new file mode 100644
index 0000000..e7d4fbe
--- /dev/null
+++ b/unit-tests/src/test_io.c
@@ -0,0 +1,53 @@
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <cmocka.h>
+
+#include "gpg_vars.h"
+
+static int setup(void **state) {
+    (void) state;
+
+    // Init tests
+    gpg_io_discard(1);
+    return 0;
+}
+
+static void test_io(void **state) {
+    (void) state;
+
+    unsigned int v32 = 0x789ABCDE;
+    unsigned int v16 = 0x3456;
+    unsigned int v8 = 0x12;
+
+    gpg_io_insert_u8(v8);
+
+    gpg_io_insert_u16(v16);
+
+    // Mark the current offset
+    gpg_io_mark();
+
+    gpg_io_insert_u32(v32);
+
+    // rewind offset to the beginning to the buffer
+    gpg_io_set_offset(0);
+
+    assert_int_equal(gpg_io_fetch_u8(), v8);
+    assert_int_equal(gpg_io_fetch_u16(), v16);
+    assert_int_equal(gpg_io_fetch_u32(), v32);
+
+    // rewind offset to the mark
+    gpg_io_set_offset(IO_OFFSET_MARK);
+
+    assert_int_equal(gpg_io_fetch_u32(), v32);
+}
+
+int main() {
+    const struct CMUnitTest tests[] = {cmocka_unit_test_setup(test_io, setup)};
+
+    return cmocka_run_group_tests(tests, NULL, NULL);
+}