sm4 加解密示例

 int do_crypt(char *outfile)
         {
         unsigned char outbuf[];
         int outlen, tmplen;
         /* Bogus key and IV: we'd normally set these from
          * another source.
          */
         unsigned char key[] = {,,,,,,,,,,,,,,,};
         unsigned char iv[] = {,,,,,,,};
         char intext[] = "Some Crypto Text";
         EVP_CIPHER_CTX *ctx;
         FILE *out;

         ctx = EVP_CIPHER_CTX_new();
         EVP_EncryptInit_ex(ctx, EVP_idea_cbc(), NULL, key, iv);

         if(!EVP_EncryptUpdate(ctx, outbuf, &outlen, intext, strlen(intext)))
                 {
                 /* Error */
                 return ;
                 }
         /* Buffer passed to EVP_EncryptFinal() must be after data just
          * encrypted to avoid overwriting it.
          */
         if(!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen))
                 {
                 /* Error */
                 return ;
                 }
         outlen += tmplen;
         EVP_CIPHER_CTX_free(ctx);
         /* Need binary mode for fopen because encrypted data is
          * binary data. Also cannot use strlen() on it because
          * it won't be null terminated and may contain embedded
          * nulls.
          */
         out = fopen(outfile, "wb");
         fwrite(outbuf, , outlen, out);
         fclose(out);
         return ;
         }

  int do_crypt(FILE *in, FILE *out, int do_encrypt)
         {
         /* Allow enough space in output buffer for additional block */
         unsigned char inbuf[], outbuf[ + EVP_MAX_BLOCK_LENGTH];
         int inlen, outlen;
         EVP_CIPHER_CTX *ctx;
         /* Bogus key and IV: we'd normally set these from
          * another source.
          */
         unsigned char key[] = "0123456789abcdeF";
         unsigned char iv[] = "";

         /* Don't set key or IV right away; we want to check lengths */
         ctx = EVP_CIPHER_CTX_new();
         EVP_CipherInit_ex(&ctx, EVP_aes_128_cbc(), NULL, NULL, NULL,
                 do_encrypt);
         OPENSSL_assert(EVP_CIPHER_CTX_key_length(ctx) == );
         OPENSSL_assert(EVP_CIPHER_CTX_iv_length(ctx) == );

         /* Now we can set key and IV */
         EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt);

         for(;;)
                 {
                 inlen = fread(inbuf, , , in);
                 if (inlen <= ) break;
                 if(!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf, inlen))
                         {
                         /* Error */
                         EVP_CIPHER_CTX_free(ctx);
                         return ;
                         }
                 fwrite(outbuf, , outlen, out);
                 }
         if(!EVP_CipherFinal_ex(ctx, outbuf, &outlen))
                 {
                 /* Error */
                 EVP_CIPHER_CTX_free(ctx);
                 return ;
                 }
         fwrite(outbuf, , outlen, out);

         EVP_CIPHER_CTX_free(ctx);
         return ;
         }

// openssl.org/docs/man1.1.0/man3/EVP_EncryptInit_ex.html