AES128 GCM C代码

AES128-GCM是一种高级加密标准（Advanced Encryption Standard）与 Galois/Counter Mode (GCM) 加密模式的组合，它提供了一种既安全又高效的对称加密方案。GCM不仅能保护数据，还能同时实现认证功能。

以下是一个简单的C语言示例，展示如何使用OpenSSL库实现AES-128-GCM加解密：

#include <openssl/aes.h>
#include <openssl/gcm.h>

// AES key and IV lengths in bytes
#define KEY_LEN 16
#define IV_LEN 12

void aes_gcm_encrypt(const unsigned char* key, const unsigned char* iv,
                    const unsigned char* plaintext, size_t pt_len,
                    unsigned char* ciphertext, size_t ct_len,
                    unsigned char* tag) {
    AES_GCM_CTX gcm;
    int ret;

    // Initialize the GCM context with a key
    if ((ret = AES_GCM_init(&gcm, key, KEY_LEN)) != 0) {
        printf("AES-GCM initialization failed: %d\n", ret);
        return;
    }

    // Set the initial counter value
    gcm_ctr(&gcm, iv, IV_LEN);

    // Encrypt the data
    if ((ret = AES_GCM_encrypt(&gcm, ciphertext, &ct_len, plaintext, pt_len)) != 1) {
        printf("AES-GCM encryption failed: %d\n", ret);
        AES_GCM_cleanup(&gcm);
        return;
    }

    // Generate and store the authentication tag
    if ((ret = AES_GCM_final(&gcm, tag, NULL)) != 1) {
        printf("AES-GCM finalization failed: %d\n", ret);
        AES_GCM_cleanup(&gcm);
        return;
    }
}

void aes_gcm_decrypt(const unsigned char* key, const unsigned char* iv,
                    const unsigned char* ciphertext, size_t ct_len,
                    const unsigned char* tag, size_t tag_len,
                    unsigned char* plaintext) {
    AES_GCM_CTX gcm;
    int ret;

    // Initialize the GCM context with a key
    if ((ret = AES_GCM_init(&gcm, key, KEY_LEN)) != 0) {
        printf("AES-GCM initialization failed: %d\n", ret);
        return;
    }

    // Set the initial counter value from the ciphertext
    if ((ret = AES_GCM_processAAD(&gcm, ciphertext, ct_len - AES_GCM_TAG_LEN)) != 1) {
        printf("AES-GCM AAD processing failed: %d\n", ret);
        AES_GCM_cleanup(&gcm);
        return;
    }

    // Verify and decrypt the data
    if ((ret = AES_GCM_verify_tag(&gcm, tag, tag_len)) == 0) {
        if ((ret = AES_GCM_decrypt(&gcm, plaintext, &plaintext[ct_len], ciphertext + AES_GCM_TAG_LEN, ct_len - AES_GCM_TAG_LEN)) != 1) {
            printf("AES-GCM decryption failed: %d\n", ret);
        } else {
            printf("Decryption successful.\n");
        }
    } else {
        printf("AES-GCM tag verification failed.\n");
    }

    AES_GCM_cleanup(&gcm);
}