Final answer:
A Symmetric Key Encryption Scheme (SKES) is considered totally insecure if it can no longer ensure the confidentiality of data, either by easy key recovery, reversing the encryption without the key, or due to severe vulnerabilities that allow attacks to compromise the encryption.
Step-by-step explanation:
When an SKES, or Symmetric Key Encryption Scheme, is said to be totally insecure or totally broken, it means that the encryption method has been compromised to such an extent that it can no longer be relied upon to keep data safe. This situation can occur if an attacker can easily decrypt data or recover the secret key without authorization. A scheme can be considered insecure if any one of the following occurs: the key can be recovered quickly, the encryption can be easily reversed without the key, or if there are severe vulnerabilities that allow an attack to breach the encryption through other indirect methods. In cryptography, maintaining security means that only someone with the correct key can decrypt the encrypted data. If this is not the case, the encryption serves no practical purpose in protecting information.