How to Decrypt & Remove Password Protection from a Zip File

Unlocking secure zip archives typically requires entering a valid, owner-supplied password. Thankfully, we can build this unlocking & decryption process directly into our file processing/task management applications using the ready-to-run C/C++ code below, saving precious time in our workflow by calling a simple utility API.

We’ll first need to install libcurl in our project:

libcurl/7.75.0

After that, we can copy the below examples to structure our API call:

CURL *curl;
CURLcode res;
curl = curl_easy_init();
if(curl) {
     curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "POST");
     curl_easy_setopt(curl, CURLOPT_URL, "https://api.cloudmersive.com/convert/archive/zip/decrypt");
     curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
     curl_easy_setopt(curl, CURLOPT_DEFAULT_PROTOCOL, "https");
     struct curl_slist *headers = NULL;
     headers = curl_slist_append(headers, "zipPassword: <string>");
     headers = curl_slist_append(headers, "Content-Type: multipart/form-data");
     headers = curl_slist_append(headers, "Apikey: YOUR-API-KEY-HERE");
     curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
     curl_mime *mime;
     curl_mimepart *part;
     mime = curl_mime_init(curl);
     part = curl_mime_addpart(mime);
     curl_mime_name(part, "inputFile");
     curl_mime_filedata(part, "/path/to/file");
     curl_easy_setopt(curl, CURLOPT_MIMEPOST, mime);
     res = curl_easy_perform(curl);
     curl_mime_free(mime);
}
curl_easy_cleanup(curl);

To authenticate our request, we can supply a free-tier API key in the authorization header. We can get one by registering a free account on the Cloudmersive website (this allows up to 800 API calls per month with no additional commitment).