Consider the following Encrypted Key Exchange (EKE) protocol where A and B share a common password P, Ep denotes a symmetric key encryption algorithm using P as the encryption key, and Encpx denotes a public key encryption algorithm using PK as the encryption key. Note that PK is randomly generated by A in each session. Ep (РК) Ep (Eпсрк (К)) 1. A → B : 2. В — А: Output : K (Session key). (1) Is this protocol secure if we replace the ephemeral PK in step 1 by a digital certificate (i.e., a PK certified by a trusted CA)? Justify your answer. (2) Does this protocol provide forward secrecy? Justify your answer.

Consider the following Encrypted Key Exchange (EKE) protocol where A and B share a common password P, Ep denotes a symmetric key encryption algorithm using P as the encryption key, and Encpx denotes a public key encryption algorithm using PK as the encryption key. Note that PK is randomly generated by A in each session. Ep (РК) Ep (Eпсрк (К)) 1. A → B : 2. В — А: Output : K (Session key). (1) Is this protocol secure if we replace the ephemeral PK in step 1 by a digital certificate (i.e., a PK certified by a trusted CA)? Justify your answer. (2) Does this protocol provide forward secrecy? Justify your answer.

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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A symmetric block encryption algorithm is shown below. 16-bit blocks of plaintext P are encrypted using a 32-bit key. Encryption is defined as: C = (P EX_OR Ko) + K1 C is the ciphertext, K is the secret key, Ko is the leftmost 16 bits of K, K1 is the rightmost 16 bits of K, EX_OR is bitwise exclusive OR, and + is binary addition. a. The ciphertext C must be the same size as the plaintext P, that is, it must not be larger than 16 bits. How can this be achieved? b. Show the decryption equation. How will the encrypted message be decrypted?
Using C programming language: A Transposition Cipher A very simple transposition cipher encrypt(S, N) can be described by the following rules: If the length of S is 1 or 2, then encrypt(S, N) is S. If S is a string of N characters s1 s2 s3... sN and k = N/2, then encrypt(S)= encrypt(sk sk−1... s2 s1 ,K)+ encrypt(sN sN−1... sk+1 ,N - K) where + indicates string concatenation. For example, encrypt("Ok", 2) = "Ok" and encrypt("12345678", 8) = "34127856". Write a program to implement this cipher. The input is a file that is guaranteed to have less then 2048 characters. Code structure might look like this: #define MAX_SIZE 2048char text_buffer[MAX_SIZE];int main(){ // read file into text_buffer encrypt(text_buffer, n); // print out text_buffer return 0;}
1. We have defined a symmetric cryptography algorithm using the XOR operator. Assume our messages (before encryption) consist of only uppercase and lowercase letters, digits and blank character. In addition, assume the key size is only one byte which is an integer between 0 and 255 (inclusive). The pseudocode of the proposed encryption algorithm is as follows: Read the message // for example message=”Hi” Read the key // for example key=10 Cipher_text=[] //an empty list for i=1 to len(message): Cipher_text= Cipher_text.append(XOR(message[i],key)) Return Cipher_text Assume XOR function, takes a character and the key, then returns the result of bitwise XOR of ASCII code of the letter with the key as an (one byte) integer. For example, if message=”Hi” and key=10, then we should first calculate the ASCCI code of “H” which is 72 and find the result of (72 XOR 10) which is 66. Then the ASCCI code of “i” is 105, so the result of (105 XOR 10) is 99. Thus the Cipher_text would be…
1. We have defined a symmetric cryptography algorithm using the XOR operator. Assume our messages (before encryption) consist of only uppercase and lowercase letters, digits and blank character. In addition, assume the key size is only one byte which is an integer between 0 and 255 (inclusive). The pseudocode of the proposed encryption algorithm is as follows: Read the message // for example message=”Hi” Read the key // for example key=10 Cipher_text=[] //an empty list for i=1 to len(message): Cipher_text= Cipher_text.append(XOR(message[i],key)) Return Cipher_text Assume XOR function, takes a character and the key, then returns the result of bitwise XOR of ASCII code of the letter with the key as an (one byte) integer. For example, if message=”Hi” and key=10, then we should first calculate the ASCCI code of “H” which is 72 and find the result of (72 XOR 10) which is 66. Then the ASCCI code of “i” is 105, so the result of (105 XOR 10) is 99. Thus the Cipher_text would be…
Using public key cryptography, X adds a digital signature s to message M, encrypts <M, s>, and sends it to Y, where it is decrypted. Which one of the following sequences of keys is used for the operations? A) Encryption: X's private key followed by Y's private key; Decryption: X's public key followed by Y's public key B) Encryption: X's private key followed by Y's public key; Decryption: X's public key followed by Y's private key C) Encryption: X's public key followed by Y's private key; Decryption: Y's public key followed by X's private key D) Encryption: X's private key followed by Y's public key; Decryption: Y's private key followed by X's public key
The Reflection algorithm can be used to encrypt a C-string (character array terminated with the null character) before it is transmitted over the Internet. The Reflection algorithm works as follows: Each letter in the message is converted to the letter in that is 13 positions to the right of that letter in the English alphabet. If the end of the alphabet is reached, counting continues from the first letter in the alphabet. The case of the letters must be maintained. For example,'M' →'Z', 'x' → 'k', 'A' → 'N'The numeric characters ('0' to '9') are shifted 5 positions to the right of that number in the character set '0' to '9'. If ‘9’ is reached, counting continues from ‘0’. For example,'0' → '5', '2' →'7', '8' → '3' All other characters are left as they are. a) What would the following string be encrypted to by the Reflection algorithm?“Call me at 662-2002 Ext 85393” b) Write a function, getPosition, which finds the position of a letter in the alphabet regardless of the case of the…
Let M be the message to be sent by using RSA cryptosystem. If (n, e) is the public key and (n, d) is the private key, which of the following is the encryption function that will yield the cipher text that corresponds to M? О Е(M) — Ме mod (p - 1) (q — 1) О Е[M) — ма mod (p - 1)(q — 1) O E(M) = Me mod n О ЕМ) — Ма mod n
A messaging system reads message as 4-digit positive integer d1d2d3d4 and stores encoding of the message e1e2e3e4 for security reason. The encoding process is as follows: ei = (di+i) mod 3 For example, if message is 4590, the encoded message is 2101. Read any arbitrary message and display the encoded message in the following format: Original message = Encoded message = language : C
Suppose you’re consulting for a bank that’s concerned about fraud detection, and they come to youwith the following problem. They have a collection of n bank cards that they’ve confiscated, suspectingthem of being used in fraud. Each bank card is a small plastic object, containing a magnetic stripe withsome encrypted data, and it corresponds to a unique account in the bank. Each account can have manybank cards corresponding to it, and we’ll say that two bank cards are equivalent if they correspond to thesame account.It’s very difficult to read the account number off a bank card directly, but the bank has a high-tech “equivalence tester” that takes two bank cards and, after performing some computations, determines whether theyare equivalent.Their question is the following: among the collection of n cards, is there a set of more than n/2 of themthat are all equivalent to one another? Assume that the only feasible operations you can do with the cardsare to pick two of them and plug them…
IH A cryptography student has accidentally used the same keystream to encrypt two different messages, M1 and M2. We know that the ciphertexts are C¡ = 0x2e38ac20ƒe51b68c and C2 = 0x638cd0bla9114b4d. We also happen to know that M1 = 0x2b1d510e6a67ae98. a) What is M2 in hexadecimal? Please give your answer a leading Ox and use lowercase letters only. b) What is the keystream? Please give your answer a leading Ox and use lowercase letters only.
Msg3. B→A : B, N1, Ks, Message2, h(B, N1, Message2) Whereas: h(m) represents the digest of the message (m). {m}{K} represents the encryption of message (m) using the key (K) PK is public key N1 is a random number. 1. What are the main problems in Msg3?
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