AES-GCM

chirrupy_hamal

已于 2024-09-20 17:28:00 修改

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分类专栏：密码学文章标签：密码学

于 2024-07-23 17:33:49 首次发布

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OpenSSL 官方提供的 AES-GCM 加解密示例

下例是基于 openssl-3.0.13 编码
gcc -o aes_gcm aes_gcm.c -I/xxx/openssl/openssl-3.0.13/include -L/xxx/openssl/openssl-3.0.13/lib64 -lssl -lcrypto

#include <stdio.h>
#include <string.h>
#include <openssl/evp.h>

#define AES_KEY_SIZE 256
#define GCM_IV_SIZE  12
#define GCM_TAG_SIZE 16

void handleErrors(void)
{
  fprintf(stderr, "An error occurred\n");
  exit(1);
}

int encrypt_data(const unsigned char *plaintext, int plaintext_len
               , unsigned char *key, unsigned char *iv, int iv_len
               , unsigned char *ciphertext, unsigned char *tag)
{
  EVP_CIPHER_CTX *ctx;
  int             len;
  int             ciphertext_len;

  if (!(ctx = EVP_CIPHER_CTX_new()))
    handleErrors();

  if (1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL))
    handleErrors();

  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, iv_len, NULL))
    handleErrors();

  if (1 != EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv))
    handleErrors();

  if (1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
    handleErrors();
  ciphertext_len = len;

  if (1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
    handleErrors();
  ciphertext_len += len;

  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, GCM_TAG_SIZE, tag))
    handleErrors();

  EVP_CIPHER_CTX_free(ctx);

  return ciphertext_len;
}

int decrypt_data(const unsigned char *ciphertext, int ciphertext_len
               , unsigned char *key, unsigned char *iv, int iv_len
               , unsigned char *decryptedtext, unsigned char *tag)
{
  EVP_CIPHER_CTX *ctx;
  int             len;
  int             plaintext_len;

  if (!(ctx = EVP_CIPHER_CTX_new()))
    handleErrors();

  if (1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL))
    handleErrors();

  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, GCM_IV_SIZE, NULL))
    handleErrors();

  if (1 != EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv))
    handleErrors();

#if 0
  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, GCM_TAG_SIZE, tag))
    handleErrors();
#endif

  if (1 != EVP_DecryptUpdate(ctx, decryptedtext, &len, ciphertext, ciphertext_len))
    handleErrors();
  plaintext_len = len;

  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, GCM_TAG_SIZE, tag))
    handleErrors();

  if (1 != EVP_DecryptFinal_ex(ctx, decryptedtext + len, &len))
    handleErrors();
  plaintext_len += len;

  EVP_CIPHER_CTX_free(ctx);

  return plaintext_len;
}

int main()
{
  unsigned char *plaintext = "Hello, AES-GCM";
  unsigned char  key[AES_KEY_SIZE/8];
  unsigned char  iv[GCM_IV_SIZE];
  unsigned char  ciphertext[128];
  int            ciphertext_len;
  unsigned char  tag[GCM_TAG_SIZE];
  unsigned char  decryptedtext[128];
  int            decryptedtext_len;
  int            i;

  RAND_bytes(key, sizeof(key));
  RAND_bytes(iv, sizeof(iv));

  ciphertext_len = encrypt_data(plaintext, strlen((char *)plaintext)
                     , key, iv, GCM_IV_SIZE, ciphertext, tag);

  printf("Plaintext: %s\n", plaintext);

  printf("Ciphertext: ");
  for (i = 0; i < ciphertext_len; i++)
    printf("%02X", ciphertext[i]);
  printf("\n");

  decryptedtext_len = decrypt_data(ciphertext, ciphertext_len
                        , key, iv, GCM_IV_SIZE, decryptedtext, tag);

  decryptedtext[decryptedtext_len] = '\0';
  printf("Decrypted text: %s\n", decryptedtext);

  return 0;
}