In this problem we explore the relationship between password length and cryptographic security.Suppose a password consists of 7 ASCII characters. You can review the ASCII characters here.. There are exactly2' = 128 ASCII characters; we will assume every character in the password is ASCII (non-printing characters areallowed).What is the size of the keyspace that consists of passwords of this form?What is the equivalent key length in bits?Assuming that you could check one passwordevery 10-' seconds, what is the worst case running time for cracking this password by brute force search (in days)?Now assume that the user used only 33 characters from the keyboard. What is the keylength in bits in this case?How many days, in the worst case, would it take to break thisweaker password? You can't round to the nearest day here -- be as exact as possible.Supposing you used only 33 characters, how long is the shortest password that achieves 125 bits of security?

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Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Recall that the sponge construction describes how to turn a public random permutation into a cryptographic hash function. Once the data to be hashed has been padded, the next step is to absorb the data r bits at a time. blk = <0>while not done: xor the next r bits of data into the first r bits of blk blk = p(blk) As a convenient (but not secure because it's too small) public random permutation, lets use the AES S-box for p. What is blk after absorbing each of the following when r=4 bits. Give your answer as exactly either 2 hexadecimal digits or 8 binary digits with no spaces (eg, 0A or 00001010). Note that the data is already padded and you should restart at blk=<0> each for each computation Data: 1001 Resulting blk:____ Data 10011001 Resulting blk:_____ Data 100110011001 Resulting blk:____
Consider the following encryption scheme for a block cipher (using the notationfrequently used in class).y1 = ek(x1), y2 = ek(x1 ⊕ x2), y3 = ek(x1 ⊕ x2 ⊕ x3), etc.a. Describe the corresponding decryption scheme.b. Can encryption and/or decryption be run in parallel for this scheme?c. Taking into account that the operation of XOR is cheap, determinewhether or not this scheme improves on ECB mode or not
Consider the case of Alice sending a message, m, to Bob. Both Alice and Bob use public key cryptography and each has a public and private key as described in the text. The figure attached below shows the operations that Alice must perform to provide confidentiality, authentication, and integrity when sending a message to Bob over the network. We can use either symmetric key or public key cryptography to encrypt a message. For our purposes, either technique will encrypt the message, and applying both doesn't make it "more secure". Also, we can assume that the session key would remain a secret so the fact that it is discarded does not make it "more secure". Why do we use a session key, Ks, instead of relying only on public key Cryptography? In other words, why do we use both public key and symmetric key cryptography?
Consider an RSA key set for Alice with p = 23, q = 17, n = 391 and e = 15.a) Her public key is (e, n) = (15, 391). Is her private key (d, n) = (47, 391)? JusVfy your answer. b) Suppose Bob wants to encrypt a message 90 for Alice using RSA keys for confidenVality. Whatis the corresponding cipher text?Justify your answer.
Assume the cryptanalist has two pairs (x, y1) and (, y2) such that yl = DES(K, x) and y2 = DES(K,¤). Build a exhaustive key search which requires only 255 encryption to find out K. (This would be a slight improvement over the total number of 256 keys).
Correct and detailed answer will be Upvoted else downvoted.
The Mathematical expression of the encryption and decryption process of a Caesar cipher algorithm is expressed in equations 1 and 2 respectively. c=Ep, k (1) p=Dc,k (2) Draw the flowchart of a Ceasar Cipher cryptosystem. Write a Pseudocode to implement your flowchart in (a
4. Encryption is used to secure data messages in computer networks. One possible way of encrypting text consists of rewriting the text by including first the characters found at even indexes (starting from 0) followed by the characters stored at odd indexes, while ignoring whitespace characters. For instance, the String "Exam is fun" can be encoded using the previously explained technique as "Easfnxmiu". To be able to recover the original message based on the encrypted version of the message, some additional information should be added to the encrypted message, namely, the number of characters found at even indexes, the number of characters found at odd indexes, and the indexes at which the white space characters existed in the original message. In this way, reconsidering our previous example, the string "Exam is fun" can be encoded using the previously explained technique as "5 4 4 7 Easfnxmiu". This is particularly true since the original message had 5 characters at even indexes…
Consider the affine cipher f(p) = 3p+4 (mod 26), where p is the plaintext representation of the character under consideration. For example the plaintext of the letter A is 0, B is 1, C is 2, ... Z is 25. Use this cipher to encrypt the letters I, N, G, R (changing the numbers back to letters at the end.
Please explain your answer for both questions. For the first part n is greater than or equal to zero
Consider a very simple symmetric block encryption algorithm in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (PK₁) K₁ where C = ciphertext, K = secret key, Ko = leftmost 64 bits of K, K₁ = rightmost 64 bits of K,+ = bitwise exclusive OR, and is addition mod 264. a. Show the decryption equation. That is, show the equation for P as a function of C, Ko, and K₁. b. Suppose and adversary has access to two sets of plaintexts and their correspond- ing ciphertexts and wishes to determine K. We have the two equations: C = (PK) K₁; C = (PK) K₁ First, derive an equation in one unknown (e.g., Ko). Is it possible to proceed fur- ther to solve for Ko?
An early attempt to force users to use less predictable passwords involved computer-supplied passwords. The passwords were eight characters long and were taken from the character set consisting of lowercase letters and digits. They were generated by a pseudorandom number generator with 215 possible starting values. Using the technology of the time, the time required to search through all character strings of length 8 from a 36-character alphabet was 112 years. Unfortunately, this is not a true reflection of the actual security of the system. Explain the problem.

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