You can encrypt objects uploaded to COS in the following ways.

Using server-side encryption with COS-managed encryption keys (SSE-COS) to protect data

With this method, your master key and data are managed by COS. COS can automatically encrypt your data when written into the IDC and automatically decrypt it when accessed. Currently, COS supports AES-256 encryption using a COS master key pair.

In the SDK for C, you need to configure the encryption by specifying the x-cos-server-side-encryption header.

cpp
int main(int argc, char *argv[])
{
  cos_pool_t *p = NULL;
  int is_cname = 0;
  cos_status_t *s = NULL;
  cos_request_options_t *options = NULL;
  cos_string_t bucket;
  cos_string_t object;
  cos_table_t *resp_headers = NULL;
  cos_table_t *headers = NULL;
  cos_string_t file;
  cos_string_t download_file;
// Initialization
  if (cos_http_io_initialize(NULL, 0) != COSE_OK) {
     exit(1);
  }
  cos_pool_create(&p, NULL);
  // Initialize request options
  options = cos_request_options_create(p);
  options->config = cos_config_create(options->pool);
  cos_str_set(&options->config->endpoint, "cos.ap-guangzhou.myqcloud.com"); // Your endpoint
  cos_str_set(&options->config->access_key_id, "SECRETID");    // your SecretId 
  cos_str_set(&options->config->access_key_secret, "SECRETKEY"); // your SecretKey
  cos_str_set(&options->config->appid, "APPID");// Your APPID
  options->config->is_cname = is_cname;
  options->ctl = cos_http_controller_create(options->pool, 0);
  cos_str_set(&bucket, "<BucketName-APPID>");// Your bucket name in the format: BucketName-APPID
   // Set headers for SSE-COS encryption
  headers = cos_table_make(p, 1);
  apr_table_add(headers, "x-cos-server-side-encryption", "AES256");
   cos_str_set(&file, "example1.txt");// Your file name
  cos_str_set(&object, "example_object");// Your object name
   // Upload an object
  s = cos_put_object_from_file(options, &bucket, &object, &file, headers, &resp_headers);
  if (cos_status_is_ok(s)) {
      printf("put object succeeded\n");
  } else {
      printf("put object failed\n");
  }

  // Download an object
  cos_str_set(&download_file, "example2.txt");
  s = cos_get_object_to_file(options, &bucket, &object, NULL, NULL, &download_file, &resp_headers);
  if (cos_status_is_ok(s)) {
      printf("get object succeeded\n");
  } else {
      printf("get object failed\n");
  }

  cos_pool_destroy(p);
   cos_http_io_deinitialize();
  return 0;
}

Using server-side encryption with customer-provided encryption keys (SSE-C) to protect data

The encryption key is provided by the customer. When you upload an object, COS will apply AES-256 encryption to your data using the customer-provided encryption key pair. In this SDK, you need to configure the encryption by specifying the x-cos-server-side-encryption-customer-* header.

Note：

• This type of encryption requires using HTTPS requests.
• customerKey: the key provided by the user; this key should be a 32-byte string that contains numbers, letters, and special characters, but not Chinese characters.
• If this encryption method was used when you uploaded a file, you should also use it when you GET (download) or HEAD (query) this file.

cpp
int main(int argc, char *argv[])
{
  cos_pool_t *p = NULL;
  int is_cname = 0;
  cos_status_t *s = NULL;
  cos_request_options_t *options = NULL;
  cos_string_t bucket;
  cos_string_t object;
  cos_table_t *resp_headers = NULL;
  cos_table_t *headers = NULL;
  cos_string_t file;
  cos_string_t download_file;
// Initialization
  if (cos_http_io_initialize(NULL, 0) != COSE_OK) {
     exit(1);
  }
  cos_pool_create(&p, NULL);
  // Initialize request options
  options = cos_request_options_create(p);
  options->config = cos_config_create(options->pool);
  cos_str_set(&options->config->endpoint, "https://cos.ap-guangzhou.myqcloud.com"); // Your endpoint, which requires requests to be sent over HTTPS
  cos_str_set(&options->config->access_key_id, "SECRETID");    // your SecretId 
  cos_str_set(&options->config->access_key_secret, "SECRETKEY"); // your SecretKey
  cos_str_set(&options->config->appid, "APPID");// Your APPID
  options->config->is_cname = is_cname;
  options->ctl = cos_http_controller_create(options->pool, 0);
  cos_str_set(&bucket, "<BucketName-APPID>");// Your bucket name in the format: BucketName-APPID
   // Set headers for SSE-C encryption
  headers = cos_table_make(p, 3);
  apr_table_add(headers, "x-cos-server-side-encryption-customer-algorithm", "AES256");
  apr_table_add(headers, "x-cos-server-side-encryption-customer-key", "MDEyMzQ1Njc4OUFCQ0RFRjAxMjM0NTY3ODlBQkNERUY=");// Replace with your own base64-encoded server-side encryption key
  apr_table_add(headers, "x-cos-server-side-encryption-customer-key-MD5", "U5L61r7jcwdNvT7frmUG8g==");// Replace with the base64-encoded MD5 hash of your own server-side encryption key
   cos_str_set(&file, "example1.txt");// Your file name
  cos_str_set(&object, "example_object");// Your object name
   // Upload an object
  s = cos_put_object_from_file(options, &bucket, &object, &file, headers, &resp_headers);
  if (cos_status_is_ok(s)) {
      printf("put object succeeded\n");
  } else {
      printf("put object failed\n");
  }

  // Download an object, which also requires the headers for server-side encryption
  cos_str_set(&download_file, "example2.txt");
  s = cos_get_object_to_file(options, &bucket, &object, headers, NULL, &download_file, &resp_headers);
  if (cos_status_is_ok(s)) {
      printf("get object succeeded\n");
  } else {
      printf("get object failed\n");
  }
   cos_pool_destroy(p);
   cos_http_io_deinitialize();
  return 0;
}