A digital signature enables non‑repudiation.  Explain what this means for Alice and Bob if Bob successfully verifies a digital signature that accompanied a message from Alice. 

Alice sends a message to Bob, along with a digital signature for the message.  Which key did Alice use to generate this digital signature?

An organization has a large amount of ciphertext that was encrypted long ago using DES.  The organization is now using the Triple DES Encryption Algorithm (TDEA). An employee has access to some DES ciphertext and the key used to encrypt it.  What is the best way for the employee to decrypt this ciphertext?

The input to a simple encryption algorithm is a block of eight (8) bits, which we can represent as ABCDEFGH.  The result of a circular shift of 3 positions to the right on this data block can be represented as . 

The effective size of a key in the Data Encryption Standard (DES) algorithm is 56 bits. Explain in words how to calculate the size of the DES keyspace. 

A scheme developed by Whit Diffie, Martin Hellman, and Ralph Merkle is commonly called “Diffie‑Hellman”. What does this scheme directly enable? 

Suppose that a hacker is able to log into the administrative account for a webserver and change the configuration so that it does not accept incoming connections.  The hacker’s actions are an attack on the of the webserver.  Hint: The answer is the name of a cybersecurity service. 

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In a Feistel cipher, the substitution operation is bitwise exclusive disjunction (XOR).  The inverse operation is bitwise inclusive disjunction (OR). 

Alice wants to use RSA encryption/decryption.  What is the first step she needs to perform to generate a key pair?