A computer-implemented method for secure third-party data storage may include 1) identifying, at a server-side computing device, a request from a client system to access an encrypted file stored under a user account, 2) identifying, in response to the request, an asymmetric key pair designated for the user account that includes an encryption key and a decryption key that has been encrypted with a client-side key, 3) receiving, from the client system, the client-side key, 4) decrypting the decryption key with the client-side key, and 5) using the decryption key to access an unencrypted version of the encrypted file. Various other methods, systems, and computer-readable media are also disclosed.