Bintray offers a secure method for sending private files through the use of signed URLs and on-the-fly encryption. Users can generate a URL signing key and use the API to create a signed URL, which can be set to expire after a specified time for added security. To further protect sensitive files, Bintray allows users to attach a secret to the signed URL, enabling AES 256 CBC encryption before the file is downloaded. The recipient needs both the signed URL and the secret key, which can be shared through an alternative communication channel, to decrypt the file using an OpenSSL command line. This process ensures that even if a URL or downloaded file falls into the wrong hands, the content remains protected.