国密 SM4 加密 C 语言嵌入式实现
大家好，我是嵌入式学习菌，一名在上海嘉定深耕 ESP32、电力物联网开发的工程师。在电表、工控类嵌入式项目中，国密 SM4 加密是数据传输的硬性安全要求，今天我就结合你提供的完整可运行代码，逐行逐模块深度拆解，纯 C 实现、无第三方依赖、直接移植到 ESP32/STM32，完美适配电表 JSON 报文加密场景。
一、为什么嵌入式设备必用 SM4？
- 国密标准：我国商用密码算法，电力 / 物联网项目强制合规
- 轻量高效：16 字节密钥 + 16 字节分组，MCU 资源占用极低
- 速度快：对称加密，适合嵌入式实时数据传输
- 通用性强：ECB 模式开箱即用，适配电表 Payload 变长数据加密
二、完整代码 + 逐模块深度详解
代码完全对齐你提供的工程版本，支持字符串明文加密、PKCS7 填充、十六进制输出，直接用于项目。
完整工程代码
c
运行
#include <stdint.h> #include <string.h> #include <stdlib.h> #include <stdio.h> // ===================== SM4 标准固定参数（国密规范，禁止修改） ===================== // SM4分组长度：固定16字节 #define SM4_BLOCK_SIZE 16 // SM4密钥长度：固定16字节 #define SM4_KEY_SIZE 16 // 国密SM4官方标准S盒（算法核心置换表，固定值） static const uint8_t SM4_SBOX[256] = { 0xd6,0x90,0xe9,0xfe,0xcc,0xe1,0x3d,0xb7,0x16,0xb6,0x14,0xc2,0x28,0xfb,0x2c,0x05, 0x2b,0x67,0x9a,0x76,0x2a,0xbe,0x04,0xc3,0xaa,0x44,0x13,0x26,0x49,0x86,0x06,0x99, 0x9c,0x42,0x50,0xf4,0x91,0xef,0x98,0x7a,0x33,0x54,0x0b,0x43,0xed,0xcf,0xac,0x62, 0xe4,0xb3,0x1c,0xa9,0xc9,0x08,0xe8,0x95,0x80,0xdf,0x94,0xfa,0x75,0x8f,0x3f,0xa6, 0x47,0x07,0xa7,0xfc,0xf3,0x73,0x17,0xba,0x83,0x59,0x3c,0x19,0xe6,0x85,0x4f,0xa8, 0x68,0x6b,0x81,0xb2,0x71,0x64,0xda,0x8b,0xf8,0xeb,0x0f,0x4b,0x70,0x56,0x9d,0x35, 0x1e,0x24,0x0e,0x5e,0x63,0x58,0xd1,0xa2,0x25,0x22,0x7c,0x3b,0x01,0x21,0x78,0x87, 0xd4,0x00,0x46,0x57,0x9f,0xd3,0x27,0x52,0x4c,0x36,0x02,0xe7,0xa0,0xc4,0xc8,0x9e, 0xea,0xbf,0x8a,0xd2,0x40,0xc7,0x38,0xb5,0xa3,0xf7,0xf2,0xce,0xf9,0x61,0x15,0xa1, 0xe0,0xae,0x5d,0xa4,0x9b,0x34,0x1a,0x55,0xad,0x93,0x32,0x30,0xf5,0x8c,0xb1,0xe3, 0x1d,0xf6,0xe2,0x2e,0x82,0x66,0xca,0x60,0xc0,0x29,0x23,0xab,0x0d,0x53,0x4e,0x6f, 0xd5,0xdb,0x37,0x45,0xde,0xfd,0x8e,0x2f,0x03,0xff,0x6a,0x72,0x6d,0x6c,0x5b,0x51, 0x8d,0x1b,0xaf,0x92,0xbb,0xdd,0xbc,0x7f,0x11,0xd9,0x5c,0x41,0x1f,0x10,0x5a,0xd8, 0x0a,0xc1,0x31,0x88,0xa5,0xcd,0x7b,0xbd,0x2d,0x74,0xd0,0x12,0xb8,0xe5,0xb4,0xb0, 0x89,0x69,0x