Name Question 1 Answer: The Following Short Answer Questions

Namequestion 1answer The Following Short Answer Questions Which Of

Answer the following short-answer questions: Which of the following is not the principal goal of cryptography? Select among Confidentiality, Integrity, Availability. Which of the following is the principal goal of encryption? Select among Confidentiality, Integrity, Availability. What is a cipher? How many keys are used in a secure communication between two parties that use a symmetric-key encryption algorithm? What might be the size of an encrypted message, if the size of the plain text is 15 bits? You can choose more than one. Select among 14 bits, 15 bits, 16 bits.

Explain the Caesar cipher and the possible keys used by giving an example.

Describe the terms permutation, substitution, and the mode of operation. Provide examples of these terms in the context of the Vigenère Cipher.

Paper For Above instruction

Cryptography is a fundamental facet of information security, aiming primarily to safeguard data confidentiality, integrity, and availability. Notably, while confidentiality and integrity are classic goals within cryptography, availability often stands outside its principal objectives, focusing more on ensuring access to information rather than its protection. Understanding the core principles of cryptography and encryption involves examining various techniques such as ciphers, which are algorithms used to transform plaintext into encrypted messages, or ciphertext. These mechanisms rely on keys—either symmetric or asymmetric—to perform encryption and decryption operations.

In the context of secure communication, symmetric-key encryption utilizes a single key shared secretly between parties. This method requires both parties to possess the same cryptographic key to encrypt and decrypt messages, making key management vital. For example, if Alice and Bob agree on a secret key, they can securely exchange messages by transforming plaintext into ciphertext and vice versa using algorithms like DES or AES. Typically, the key length influences the security level; a common symmetric key length is 128 bits, which offers substantial security against brute-force attacks.

Concerning message size, the encrypted message's length often correlates with the plaintext but may vary depending on the encryption mode and padding schemes. Given a plaintext of 15 bits, the ciphertext could be 14, 15, or 16 bits depending on the encryption algorithm's block size or padding, although most encryption schemes use fixed block sizes such as 16 bits or more. Variations depend on the specific cipher design and implementation choices.

Another fundamental cipher is the Caesar cipher, an early and straightforward substitution cipher where each letter in the plaintext is shifted by a fixed number of positions in the alphabet. For example, with a shift of 3, 'A' becomes 'D', 'B' becomes 'E', and so forth. The key in this cipher is the number of positions shifted, which can range from 1 to 25 in a standard alphabet. For illustration, a shift of 3 transforms 'HELLO' into 'KHOOR'. Despite its simplicity, the Caesar cipher demonstrates the principles of substitution and key-based encryption, laying groundwork for more complex techniques.

Permutation, substitution, and modes of operation are critical concepts in cryptography. Permutation involves rearranging the positions of bits or characters within the data, enhancing diffusion. Substitution, on the other hand, replaces elements with other elements; the Caesar cipher is a classic substitution cipher. The Vigenère cipher combines these techniques iteratively, employing a keyword to determine the shifts applied to each letter—a repeating key produces a polyalphabetic cipher, which is more resistant to frequency analysis than simple substitution.

The mode of operation refers to the method of applying a block cipher to encrypt data larger than its block size. Common modes include ECB (Electronic Codebook), CBC (Cipher Block Chaining), and others. For example, in CBC mode, each plaintext block is XORed with the previous ciphertext block before encryption, thus chaining the blocks to improve security. The Vigenère cipher can be viewed as a type of polyalphabetic substitution, where the key determines the shift applied to each letter, effectively creating a repeating pattern that obscures frequency analysis.

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