能写上一段调用openssl库的代码吗，包括加密，解密

以下是一个使用 OpenSSL 库进行 AES 对称加密和解密的示例代码，使用的是 CBC 模式：

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

#define AES_BLOCK_SIZE 16

void encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
             unsigned char *iv, unsigned char *ciphertext) {
  EVP_CIPHER_CTX *ctx;
  int len;
  int ciphertext_len;

  /* Create and initialise the context */
  if (!(ctx = EVP_CIPHER_CTX_new())) {
    /* Handle error */
  }

  /* Initialise the encryption operation */
  if (1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv)) {
    /* Handle error */
  }

  /* Provide the message to be encrypted, and obtain the encrypted output */
  if (1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len)) {
    /* Handle error */
  }
  ciphertext_len = len;

  /* Finalise the encryption */
  if (1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) {
    /* Handle error */
  }
  ciphertext_len += len;

  /* Clean up */
  EVP_CIPHER_CTX_free(ctx);
}

void decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
             unsigned char *iv, unsigned char *plaintext) {
  EVP_CIPHER_CTX *ctx;
  int len;
  int plaintext_len;

  /* Create and initialise the context */
  if (!(ctx = EVP_CIPHER_CTX_new())) {
    /* Handle error */
  }

  /* Initialise the decryption operation */
  if (1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv)) {
    /* Handle error */
  }

  /* Provide the message to be decrypted, and obtain the plaintext output */
  if (1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len)) {
    /* Handle error */
  }
  plaintext_len = len;

  /* Finalise the decryption */
  if (1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len)) {
    /* Handle error */
  }
  plaintext_len += len;

  /* Clean up */
  EVP_CIPHER_CTX_free(ctx);
}

int main() {
  unsigned char *key = (unsigned char *)"01234567890123456789012345678901";
  unsigned char *iv = (unsigned char *)"0123456789012345";
  unsigned char plaintext[] = "The quick brown fox jumps over the lazy dog";
  unsigned char ciphertext[128];
  unsigned char decryptedtext[128];
  int decryptedtext_len, ciphertext_len;

  /* Encrypt the plaintext */
  encrypt(plaintext, strlen((char *)plaintext), key, iv, ciphertext);

  /* Decrypt the ciphertext */
  decrypt(ciphertext, ciphertext_len, key, iv, decryptedtext);

  /* Add a NULL terminator. We are expecting printable text */
  decryptedtext[decryptedtext_len] = '\0';

  printf("Ciphertext is:\n");
  BIO_dump_fp(stdout, (const char *)ciphertext, ciphertext_len);

  printf("Decrypted text is:\n");
  printf("%s\n", decryptedtext);

  return 0;
}

请注意，这只是一个示例代码，仅用于演示如何使用 OpenSSL 库进行加密和解密。您需要根据自己的需求对代码进行修改。同时，为了确保安全性，请务必注意密钥的生成和存储，以及加密和解密的数据完整性。