feat(mam): Implement ECDH for MAM key exchange

For DLTcollab#560

common/ta_errors.c

@@ -197,6 +197,14 @@ const char* ta_error_to_string(status_t err) {
     case SC_ENDPOINT_DNS_RESOLVE_ERROR:
       return "Error occurred when resolving the domain name";
 
+    // Crypto
+    case SC_CRYPTO_RAND_ERR:
+      return "Failed to generate random number generator";
+    case SC_CRYPTO_GEN_KEY:
+      return "Failed to generate ECDH public key";
+    case SC_CRYPTO_SECRET_ERR:
+      return "Failed to compute ECDH shared secret";
+
     default:
       return "Unknown error.";
   }

common/ta_errors.h

@@ -57,6 +57,7 @@ extern "C" {
 #define SC_MODULE_STORAGE (0x0A << SC_MODULE_SHIFT)
 #define SC_MODULE_CORE (0x0B << SC_MODULE_SHIFT)
 #define SC_MODULE_ENDPOINT (0x0C << SC_MODULE_SHIFT)
+#define SC_MODULE_CRYPTO (0x0D << SC_MODULE_SHIFT)
 /** @} */
 
 /** @name serverity code */
@@ -255,6 +256,14 @@ typedef enum {
   SC_ENDPOINT_DNS_RESOLVE_ERROR = 0x0B | SC_MODULE_ENDPOINT | SC_SEVERITY_FATAL,
   /**< Failed to resolve the domain name address */
 
+  // Crypto module
+  SC_CRYPTO_RAND_ERR = 0x01 | SC_MODULE_CRYPTO | SC_SEVERITY_FATAL,
+  /**< Failed to generate random number generator */
+  SC_CRYPTO_GEN_KEY = 0x02 | SC_MODULE_CRYPTO | SC_SEVERITY_FATAL,
+  /**< Failed to generate ECDH public key */
+  SC_CRYPTO_SECRET_ERR = 0x03 | SC_MODULE_CRYPTO | SC_SEVERITY_FATAL,
+  /**< Failed to compute ECDH shared secret */
+
 } status_t;
 
 typedef enum {

crypto/BUILD

@@ -0,0 +1,10 @@
+cc_library(
+    name = "ecdh",
+    srcs = ["ecdh.c"],
+    hdrs = ["ecdh.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//common",
+        "@mbedtls",
+    ],
+)

crypto/ecdh.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2020 BiiLabs Co., Ltd. and Contributors
+ * All Rights Reserved.
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the MIT license. A copy of the license can be found in the file
+ * "LICENSE" at the root of this distribution.
+ */
+#include "ecdh.h"
+
+#define ECDH_LOGGER "ecdh"
+static logger_id_t logger_id;
+
+void ecdh_logger_init() { logger_id = logger_helper_enable(ECDH_LOGGER, LOGGER_DEBUG, true); }
+
+int ecdh_logger_release() {
+  logger_helper_release(logger_id);
+  return 0;
+}
+
+status_t rand_num_gen_init(mbedtls_entropy_context *entropy, mbedtls_ctr_drbg_context *ctr_drbg, char *rand_seed,
+                           uint16_t seed_len) {
+  int ret = 1;
+  status_t sc = SC_OK;
+
+  mbedtls_ctr_drbg_init(ctr_drbg);
+  mbedtls_entropy_init(entropy);
+
+  if ((ret = mbedtls_ctr_drbg_seed(ctr_drbg, mbedtls_entropy_func, entropy, (const unsigned char *)rand_seed,
+                                   seed_len)) != 0) {
+    ta_log_error("mbedtls_ctr_drbg_seed returned %d\n", ret);
+    sc = SC_CRYPTO_RAND_ERR;
+  }
+
+  return sc;
+}
+
+status_t ecdh_gen_public_key(mbedtls_ecdh_context *ctx, mbedtls_ctr_drbg_context *ctr_drbg, unsigned char *pkey) {
+  int ret = 1;
+  status_t sc = SC_OK;
+
+  ret = mbedtls_ecp_group_load(&ctx->grp, MBEDTLS_ECP_DP_CURVE25519);
+  if (ret != 0) {
+    ta_log_error("mbedtls_ecp_group_load returned %d\n", ret);
+    sc = SC_CRYPTO_GEN_KEY;
+    goto exit;
+  }
+
+  ret = mbedtls_ecdh_gen_public(&ctx->grp, &ctx->d, &ctx->Q, mbedtls_ctr_drbg_random, ctr_drbg);
+  if (ret != 0) {
+    ta_log_error("mbedtls_ecdh_gen_public returned %d\n", ret);
+    sc = SC_CRYPTO_GEN_KEY;
+    goto exit;
+  }
+
+  ret = mbedtls_mpi_write_binary(&ctx->Q.X, pkey, SHARE_DATA_LEN);
+  if (ret != 0) {
+    ta_log_error("mbedtls_mpi_write_binary returned %d\n", ret);
+    sc = SC_CRYPTO_GEN_KEY;
+  }
+
+exit:
+  return sc;
+}
+
+status_t ecdh_compute_shared_secret(mbedtls_ecdh_context *ctx, mbedtls_ctr_drbg_context *ctr_drbg,
+                                    unsigned char *input_shared_data) {
+  int ret = 1;
+  status_t sc = SC_OK;
+
+  ret = mbedtls_mpi_lset(&ctx->Qp.Z, 1);
+  if (ret != 0) {
+    ta_log_error("mbedtls_mpi_lset returned %d\n", ret);
+    sc = SC_CRYPTO_SECRET_ERR;
+    goto exit;
+  }
+
+  ret = mbedtls_mpi_read_binary(&ctx->Qp.X, input_shared_data, SHARE_DATA_LEN);
+  if (ret != 0) {
+    ta_log_error("mbedtls_mpi_read_binary returned %d\n", ret);
+    sc = SC_CRYPTO_SECRET_ERR;
+    goto exit;
+  }
+
+  ret = mbedtls_ecdh_compute_shared(&ctx->grp, &ctx->z, &ctx->Qp, &ctx->d, mbedtls_ctr_drbg_random, ctr_drbg);
+  if (ret != 0) {
+    ta_log_error("mbedtls_ecdh_compute_shared returned %d\n", ret);
+    sc = SC_CRYPTO_SECRET_ERR;
+  }
+
+exit:
+  return sc;
+}
+
+void rand_num_gen_release(mbedtls_entropy_context *entropy, mbedtls_ctr_drbg_context *ctr_drbg) {
+  mbedtls_ctr_drbg_free(ctr_drbg);
+  mbedtls_entropy_free(entropy);
+}

crypto/ecdh.h

@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2020 BiiLabs Co., Ltd. and Contributors
+ * All Rights Reserved.
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the MIT license. A copy of the license can be found in the file
+ * "LICENSE" at the root of this distribution.
+ */
+
+#ifndef ECDH_COMMON_H
+#define ECDH_COMMON_H
+
+#include "common/logger.h"
+#include "common/ta_errors.h"
+#include "mbedtls/config.h"
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/ecdh.h"
+#include "mbedtls/entropy.h"
+#include "mbedtls/platform.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define SHARE_DATA_LEN 32
+
+typedef struct rand_gen_s {
+  mbedtls_entropy_context entropy;
+  mbedtls_ctr_drbg_context ctr_drbg;
+} rand_gen_t;
+
+/**
+ * Initialize logger for ECDH
+ */
+void ecdh_logger_init();
+
+/**
+ * Release logger
+ *
+ * @return
+ * - zero on success
+ * - EXIT_FAILURE on error
+ */
+int ecdh_logger_release();
+
+/**
+ * @brief Initialize mbedtls random number generator
+ *
+ * @param[in] entropy Entropy contrext for randomess
+ * @param[in] ctr_drbg Counter-mode block-cipher-based Deterministic Random Bit Generator object
+ * @param[in] rand_seed Random seed for random number generator
+ * @param[in] seed_len The length of random seed
+ *
+ * @return
+ * - SC_OK on success
+ * - non-zero on error
+ */
+status_t rand_num_gen_init(mbedtls_entropy_context *entropy, mbedtls_ctr_drbg_context *ctr_drbg, char *rand_seed,
+                           uint16_t seed_len);
+
+/**
+ * @brief Initialize ECDH context and generate ECDH keypair
+ *
+ * @param[in] ctx ECDH context
+ * @param[in] ctr_drbg Counter-mode block-cipher-based Deterministic Random Bit Generator object
+ * @param[out] pkey Output public key which would be sent to counterpart
+ *
+ * @return
+ * - SC_OK on success
+ * - non-zero on error
+ */
+status_t ecdh_gen_public_key(mbedtls_ecdh_context *ctx, mbedtls_ctr_drbg_context *ctr_drbg, unsigned char *pkey);
+
+/**
+ * @brief Compute the shared secret by Diffie–Hellman key exchange protocol
+ *
+ * @param[in] ctx ECDH context
+ * @param[in] ctr_drbg Counter-mode block-cipher-based Deterministic Random Bit Generator object
+ * @param[in] input_shared_data The public key sent by counterpart
+ *
+ * @return
+ * - SC_OK on success
+ * - non-zero on error
+ */
+status_t ecdh_compute_shared_secret(mbedtls_ecdh_context *ctx, mbedtls_ctr_drbg_context *ctr_drbg,
+                                    unsigned char *input_shared_data);
+
+/**
+ * @brief Release random number generator
+ *
+ * @param[in] entropy Entropy contrext for randomess
+ * @param[in] ctr_drbg Counter-mode block-cipher-based Deterministic Random Bit Generator object
+ *
+ * @return
+ * - SC_OK on success
+ * - non-zero on error
+ */
+void rand_num_gen_release(mbedtls_entropy_context *entropy, mbedtls_ctr_drbg_context *ctr_drbg);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // ECDH_COMMON_H

tests/unit-test/BUILD

@@ -98,3 +98,13 @@ cc_test(
         "//utils:tryte_byte_conv",
     ],
 )
+
+cc_test(
+    name = "test_ecdh",
+    srcs = ["test_ecdh.c"],
+    deps = [
+        "//crypto:ecdh",
+        "//tests:test_define",
+        "@mbedtls",
+    ],
+)

tests/unit-test/test_ecdh.c

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2020 BiiLabs Co., Ltd. and Contributors
+ * All Rights Reserved.
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the MIT license. A copy of the license can be found in the file
+ * "LICENSE" at the root of this distribution.
+ */
+
+#include "crypto/ecdh.h"
+#include "tests/test_define.h"
+
+void test_srv_cli_communication(void) {
+  rand_gen_t rand_gen;
+  mbedtls_ecdh_context ecdh_srv, ecdh_cli;
+  unsigned char cli_to_srv[SHARE_DATA_LEN], srv_to_cli[SHARE_DATA_LEN];
+
+  // initialize ECDH object for server side and client side
+  mbedtls_ecdh_init(&ecdh_srv);
+  mbedtls_ecdh_init(&ecdh_cli);
+
+  TEST_ASSERT_EQUAL_INT32(SC_OK,
+                          rand_num_gen_init(&rand_gen.entropy, &rand_gen.ctr_drbg, TEST_UUID, strlen(TEST_UUID) + 1));
+
+  // [client] initialize ECDH context and generate public key
+  TEST_ASSERT_EQUAL_INT32(SC_OK, ecdh_gen_public_key(&ecdh_cli, &rand_gen.ctr_drbg, cli_to_srv));
+
+  // [server] initialize ECDH context and generate public key
+  TEST_ASSERT_EQUAL_INT32(SC_OK, ecdh_gen_public_key(&ecdh_srv, &rand_gen.ctr_drbg, srv_to_cli));
+
+  // [server] compute shared secret with peer's public key
+  TEST_ASSERT_EQUAL_INT32(SC_OK, ecdh_compute_shared_secret(&ecdh_srv, &rand_gen.ctr_drbg, cli_to_srv));
+
+  // [client] compute shared secret with peer's public key
+  TEST_ASSERT_EQUAL_INT32(SC_OK, ecdh_compute_shared_secret(&ecdh_cli, &rand_gen.ctr_drbg, srv_to_cli));
+
+  // Check if the two shared secret are the same
+  TEST_ASSERT_EQUAL_INT32(0, mbedtls_mpi_cmp_mpi(&ecdh_cli.z, &ecdh_srv.z));
+
+  rand_num_gen_release(&rand_gen.entropy, &rand_gen.ctr_drbg);
+  mbedtls_ecdh_free(&ecdh_srv);
+  mbedtls_ecdh_free(&ecdh_cli);
+}
+
+int main(void) {
+  UNITY_BEGIN();
+
+  // Initialize logger
+  if (ta_logger_init() != SC_OK) {
+    return EXIT_FAILURE;
+  }
+
+  ecdh_logger_init();
+  RUN_TEST(test_srv_cli_communication);
+  ecdh_logger_release();
+
+  return UNITY_END();
+}