mbedtls系列文章

Demo工程源码

本工程基于STM32L41RCT6开发板，包含了本系列文章中所编写的所有Demo，持续更新……

文章目录

一、DH秘钥协商算法

DH是一种秘钥协商算法，使得通信双方在不安全通道交换共享参数，从而协商出一个会话秘钥。

DH秘钥协商的过程如下：

① 通信双方A和B确认共享参数；

② A生成随机秘钥x；

③ B生成随机秘钥y；

④ A计算共享秘钥；

⑤ B计算共享秘钥；

DH秘钥协商算法可以有效防止中间窃听者，但是无法方式中间拦截者。

二、DH秘钥协商功能的配置和使用

1. 配置宏

使用DH秘钥协商功能需要提前开启伪随机数生成器（依赖AES算法、SHA256算法、MD通用接口），其中伪随机数生成器的硬件适配移植实现已经讲述，请参考对应的第二篇博客，不再赘述。

综合上述，本实验中需要开启的宏如下表：

宏定义	功能
MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES	不使用默认熵源（如果已有、要屏蔽该宏）
MBEDTLS_NO_PLATFORM_ENTROPY	不使用系统内置熵源
MBEDTLS_AES_C	使用AES算法
MBEDTLS_ENTROPY_C	使能熵源模块
MBEDTLS_CTR_DRBG_C	使能随机数模块
MBEDTLS_SHA256_C	使能SHA256算法
MBEDTLS_MD_C	开启MD通用接口
MBEDTLS_AES_ROM_TABLES	使能预定义S盒（节约内存空间）
MBEDTLS_BIGNUM_C	开启大数运算
MBEDTLS_GENPRIME	开启生成素数
MBEDTLS_DHM_C	开启DH秘钥协商模块

下面补充几个一个第一次出现宏的定义。

① MBEDTLS_DHM_C

/** * \def MBEDTLS_DHM_C * * Enable the Diffie-Hellman-Merkle module. * * Module:  library/dhm.c * Caller:  library/ssl_cli.c *          library/ssl_srv.c * * This module is used by the following key exchanges: *      DHE-RSA, DHE-PSK * * \warning    Using DHE constitutes a security risk as it *             is not possible to validate custom DH parameters. *             If possible, it is recommended users should consider *             preferring other methods of key exchange. *             See dhm.h for more details. * */#define MBEDTLS_DHM_C

编辑针对本实验的配置文件mbedtls_config_dhm.h：

/** * @brief   Minimal configuration for DHM Function * @author  mculover666 * @date    2020/09/28*/#ifndef _MBEDTLS_CONFIG_DHM_H_#define _MBEDTLS_CONFIG_DHM_H_/* System support */#define MBEDTLS_HAVE_ASM//#define MBEDTLS_HAVE_TIME/* mbed feature support */#define MBEDTLS_ENTROPY_HARDWARE_ALT//#define MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES#define MBEDTLS_NO_PLATFORM_ENTROPY/* mbed modules */#define MBEDTLS_AES_C#define MBEDTLS_AES_ROM_TABLES#define MBEDTLS_CTR_DRBG_C#define MBEDTLS_ENTROPY_C#define MBEDTLS_SHA256_C#define MBEDTLS_MD_C#define MBEDTLS_BIGNUM_C#define MBEDTLS_GENPRIME#define MBEDTLS_DHM_C#include "mbedtls/check_config.h"#endif /* _MBEDTLS_CONFIG_DHM_H_ */

在MDK配置mbedtls使用该配置文件：

2. DH秘钥协商功能API说明

使用该功能模块需要包含头文件：

#include "mbedtls/dhm.h"

① 初始化DH结构体：

/** * \brief          This function initializes the DHM context. * * \param ctx      The DHM context to initialize. */void mbedtls_dhm_init( mbedtls_dhm_context *ctx );

② 生成公开参数：

/** * \brief          This function creates a DHM key pair and exports *                 the raw public key in big-endian format. * * \note           The destination buffer is always fully written *                 so as to contain a big-endian representation of G^X mod P. *                 If it is larger than \c ctx->len, it is padded accordingly *                 with zero-bytes at the beginning. * * \param ctx      The DHM context to use. This must be initialized and *                 have the DHM parameters set. It may or may not already *                 have imported the peer's public key. * \param x_size   The private key size in Bytes. * \param output   The destination buffer. This must be a writable buffer of *                 size \p olen Bytes. * \param olen     The length of the destination buffer. This must be at least *                 equal to `ctx->len` (the size of \c P). * \param f_rng    The RNG function. This must not be \c NULL. * \param p_rng    The RNG context to be passed to \p f_rng. This may be \c NULL *                 if \p f_rng doesn't need a context argument. * * \return         \c 0 on success. * \return         An \c MBEDTLS_ERR_DHM_XXX error code on failure. */int mbedtls_dhm_make_public( mbedtls_dhm_context *ctx, int x_size,                     unsigned char *output, size_t olen,                     int (*f_rng)(void *, unsigned char *, size_t),                     void *p_rng );

③ 读取公开参数：

/** * \brief          This function imports the raw public value of the peer. * * \note           In a TLS handshake, this is the how the server imports *                 the Client's public DHM key. * * \param ctx      The DHM context to use. This must be initialized and have *                 its DHM parameters set, e.g. via mbedtls_dhm_set_group(). *                 It may or may not already have generated its own private key. * \param input    The input buffer containing the \c G^Y value of the peer. *                 This must be a readable buffer of size \p ilen Bytes. * \param ilen     The size of the input buffer \p input in Bytes. * * \return         \c 0 on success. * \return         An \c MBEDTLS_ERR_DHM_XXX error code on failure. */int mbedtls_dhm_read_public( mbedtls_dhm_context *ctx,                     const unsigned char *input, size_t ilen );

④ 计算共享秘钥：

/** * \brief          This function derives and exports the shared secret *                 \c (G^Y)^X mod \c P. * * \note           If \p f_rng is not \c NULL, it is used to blind the input as *                 a countermeasure against timing attacks. Blinding is used *                 only if our private key \c X is re-used, and not used *                 otherwise. We recommend always passing a non-NULL *                 \p f_rng argument. * * \param ctx           The DHM context to use. This must be initialized *                      and have its own private key generated and the peer's *                      public key imported. * \param output        The buffer to write the generated shared key to. This *                      must be a writable buffer of size \p output_size Bytes. * \param output_size   The size of the destination buffer. This must be at *                      least the size of \c ctx->len (the size of \c P). * \param olen          On exit, holds the actual number of Bytes written. * \param f_rng         The RNG function, for blinding purposes. This may *                      b \c NULL if blinding isn't needed. * \param p_rng         The RNG context. This may be \c NULL if \p f_rng *                      doesn't need a context argument. * * \return              \c 0 on success. * \return              An \c MBEDTLS_ERR_DHM_XXX error code on failure. */int mbedtls_dhm_calc_secret( mbedtls_dhm_context *ctx,                     unsigned char *output, size_t output_size, size_t *olen,                     int (*f_rng)(void *, unsigned char *, size_t),                     void *p_rng );

⑤ 释放DH结构体：

/** * \brief          This function frees and clears the components *                 of a DHM context. * * \param ctx      The DHM context to free and clear. This may be \c NULL, *                 in which case this function is a no-op. If it is not \c NULL, *                 it must point to an initialized DHM context. */void mbedtls_dhm_free( mbedtls_dhm_context *ctx );

⑥ 错误码：

#define MBEDTLS_ERR_DHM_BAD_INPUT_DATA                    -0x3080  /**< Bad input parameters. */#define MBEDTLS_ERR_DHM_READ_PARAMS_FAILED                -0x3100  /**< Reading of the DHM parameters failed. */#define MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED                -0x3180  /**< Making of the DHM parameters failed. */#define MBEDTLS_ERR_DHM_READ_PUBLIC_FAILED                -0x3200  /**< Reading of the public values failed. */#define MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED                -0x3280  /**< Making of the public value failed. */#define MBEDTLS_ERR_DHM_CALC_SECRET_FAILED                -0x3300  /**< Calculation of the DHM secret failed. */#define MBEDTLS_ERR_DHM_INVALID_FORMAT                    -0x3380  /**< The ASN.1 data is not formatted correctly. */#define MBEDTLS_ERR_DHM_ALLOC_FAILED                      -0x3400  /**< Allocation of memory failed. */#define MBEDTLS_ERR_DHM_FILE_IO_ERROR                     -0x3480  /**< Read or write of file failed. *//* MBEDTLS_ERR_DHM_HW_ACCEL_FAILED is deprecated and should not be used. */#define MBEDTLS_ERR_DHM_HW_ACCEL_FAILED                   -0x3500  /**< DHM hardware accelerator failed. */#define MBEDTLS_ERR_DHM_SET_GROUP_FAILED                  -0x3580  /**< Setting the modulus and generator failed. */

3. 编写测试函数

新建测试文件``，编写以下测试内容，其中服务器和客户端之间直接通信，没有采用网络通信：

/** * @brief   DHM Function demo * @author  mculover666 * @date    2020/09/28*/#if !defined(MBEDTLS_CONFIG_FILE)#include "mbedtls/config.h"#else#include MBEDTLS_CONFIG_FILE#endif#if defined(MBEDTLS_DHM_C)#include 
   
    #include "string.h"#include "mbedtls/entropy.h"#include "mbedtls/ctr_drbg.h"#include "mbedtls/dhm.h"#define GENERATOR   "2"#define T_P          "FFFFFFFFFFFFFFFFADF85458A2BB4A9AAFDC5620273D3CF1D8B9C583CE2D3695" \                     "A9E13641146433FBCC939DCE249B3EF97D2FE363630C75D8F681B202AEC4617A"\                     "D3DF1ED5D5FD65612433F51F5F066ED0856365553DED1AF3B557135E7F57C935"\                     "984F0C70E0E68B77E2A689DAF3EFE8721DF158A136ADE73530ACCA4F483A797A"\                     "BC0AB182B324FB61D108A94BB2C8E3FBB96ADAB760D7F4681D4F42A3DE394DF4"\                     "AE56EDE76372BB190B07A7C8EE0A6D709E02FCE1CDF7E2ECC03404CD28342F61"\                     "9172FE9CE98583FF8E4F1232EEF28183C3FE3B1B4C6FAD733BB5FCBC2EC22005"\                     "C58EF1837D1683B2C6F34A26C1B2EFFA886B423861285C97FFFFFFFFFFFFFFFF"uint8_t server_pub[256];uint8_t client_pub[256];uint8_t server_secret[256];uint8_t client_secret[256];static void dump_buf(uint8_t *buf, uint32_t len){
       int i;        for (i = 0; i < len; i++) {
           printf("%s%02X%s", i % 16 == 0 ? "\r\n\t" : " ",                            buf[i],                            i == len - 1 ? "\r\n" : "");    }}int mbedtls_dhm_test(void){
       int ret;    size_t olen;       const char *pers = "dhm_test";    mbedtls_entropy_context entropy;    mbedtls_ctr_drbg_context ctr_drbg;    mbedtls_dhm_context dhm_server, dhm_client;    /* 1. init structure */    mbedtls_entropy_init(&entropy);    mbedtls_ctr_drbg_init(&ctr_drbg);    mbedtls_dhm_init(&dhm_server);    mbedtls_dhm_init(&dhm_client);        /* 2. update seed with we own interface ported */    printf( "\n  . Seeding the random number generator..." );        ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,                               (const unsigned char *) pers,                               strlen(pers));    if(ret != 0) {
           printf( " failed\n  ! mbedtls_ctr_drbg_seed returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );    /* 3. genetate 2048 bit prime(G, P) */    printf("\n  . Genetate 2048 bit prime(G, P)...");        mbedtls_mpi_read_string(&dhm_server.P, 16, T_P);    mbedtls_mpi_read_string(&dhm_server.G, 10, GENERATOR);    dhm_server.len = mbedtls_mpi_size(&dhm_server.P);        mbedtls_mpi_read_string(&dhm_client.P, 16, T_P);    mbedtls_mpi_read_string(&dhm_client.G, 10, GENERATOR);    dhm_client.len = mbedtls_mpi_size(&dhm_client.P);        printf("ok\r\n");        /* 4. Server create a DHM key pair */    printf("\n  . Server creates a DHM key pair...");        ret = mbedtls_dhm_make_public(&dhm_server, 256, server_pub, sizeof(server_pub), mbedtls_ctr_drbg_random, &ctr_drbg);    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_make_public returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );    dump_buf(server_pub, sizeof(server_pub));        /* 5. Client creates a DHM key pair */    printf("\n  . Client create a DHM key pair...");        ret = mbedtls_dhm_make_public(&dhm_client, 256, client_pub, sizeof(client_pub), mbedtls_ctr_drbg_random, &ctr_drbg);    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_make_public returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );    dump_buf(client_pub, sizeof(client_pub));        /* 6. Server Read public key pair */    printf("\n  . Server Read public key pair...");        ret = mbedtls_dhm_read_public(&dhm_server, client_pub, sizeof(client_pub));    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_read_public returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );        /* 7. Client Read public key pair */    printf("\n  . Client Read public key pair...");        ret = mbedtls_dhm_read_public(&dhm_client, server_pub, sizeof(server_pub));    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_read_public returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );         /* 8. calc the shared secret */    printf("\n  . Server calc the shared secret...");        ret = mbedtls_dhm_calc_secret(&dhm_server, server_secret, sizeof(server_secret), &olen, mbedtls_ctr_drbg_random, &ctr_drbg);    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_calc_secret returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );     dump_buf(server_secret, sizeof(server_secret));        /* 9. calc the shared secret */    printf("\n  . Client calc the shared secret...");        ret = mbedtls_dhm_calc_secret(&dhm_client, client_secret, sizeof(client_secret), &olen, mbedtls_ctr_drbg_random, &ctr_drbg);    if(ret != 0) {
           printf( " failed\n  ! mbedtls_dhm_calc_secret returned %d(-0x%04x)\n", ret, -ret);        goto exit;    }    printf( " ok\n" );     dump_buf(client_secret, sizeof(client_secret));        exit:        /* 10. release structure */    mbedtls_ctr_drbg_free(&ctr_drbg);    mbedtls_entropy_free(&entropy);    mbedtls_dhm_free(&dhm_server);    mbedtls_dhm_free(&dhm_client);        return ret;}#endif /* MBEDTLS_DHM_C */