The most secure way to ensure the deletion of encrypted data stored in the cloud is to destroy all encryption keys associated with the data. Without the encryption keys, the encrypted data becomes inaccessible and unreadable, effectively rendering it useless. This method ensures that the data cannot be recovered, even if the physical storage remains intact. According to IAPP guidelines, key destruction is a recognized method for securely disposing of encrypted data because it eliminates the possibility of data decryption. This approach aligns with best practices for data security and privacy.