In cryptography, what does the term “Avalanche Effect” signify?

The term "Avalanche Effect" in cryptography refers to the phenomenon where a small change in the input of a cryptographic function (like changing just one bit of the input) results in a substantial and unpredictable change in the output. This characteristic is essential for ensuring that the encrypted data cannot be easily analyzed or predicted, thus enhancing the security of the cryptographic algorithm.

In practical terms, if an attacker were to make a slight modification to the plaintext, the result after encryption should be drastically different from the original encrypted output. This unpredictability complicates any potential attempts at cryptanalysis, making the encryption much more robust against attacks. The Avalanche Effect is a crucial property of secure hash functions and block ciphers, providing confidence that even minor alterations to the input will lead to significantly different encrypted results, thereby safeguarding sensitive information.

The other choices do not accurately describe the Avalanche Effect. The concept does not relate to the reversibility of encryption, the uniqueness of ciphertext produced by different keys, or the determination of a key's strength based solely on its length. Each of those aspects pertains to different characteristics of cryptography but does not encapsulate the essence of the Avalanche Effect.