Final answer:
An SKES is semantically secure when it is robust enough to prevent any meaningful information from being derived from the ciphertext by attackers. The encryption must ensure ciphertext indistinguishability and typically involves randomized encryption to protect against various types of attacks.
Step-by-step explanation:
Meaning of Semantic Security in SKES
When an SKES (Symmetric Key Encryption Scheme) is said to be semantically secure, it implies that the encryption process is strong enough to prevent an attacker from deriving any meaningful information from the ciphertext. Semantic security means that, even if an attacker were to obtain multiple encrypted messages, they would not be able to figure out anything about the plaintext messages. This is sometimes referred to as ciphertext indistinguishability, where it should be infeasible for a computationally bounded adversary to distinguish between the encryptions of two arbitrary messages of their choosing, assuming that the encryption keys remain secret.The concept of semantic security is a fundamental aspect of modern cryptography and is essential for ensuring that sensitive data is not compromised. For an encryption algorithm to be considered secure in this manner, it should use cryptographic techniques such as randomized encryption, where the same plaintext encrypted multiple times results in different ciphertexts, making pattern recognition and predictions about the plaintext more difficult for an attacker.Semantic security is particularly important in scenarios where data is transmitted over insecure channels, such as the Internet, or where encrypted data might be stored in a location that could be accessed by potential attackers. Ensuring that an SKES is semantically secure helps protect against a range of attacks, including known-plaintext attacks, chosen-plaintext attacks, and ciphertext-only attacks.