It is illegal for the caller to assert en if rdy is deasserted if this happens, the behaviour of the callee is undefined. The following timing diagram illustrates this: If rdy is asserted, the caller may assert en to make a “request” to the callee. The handshake has two sides: the “caller” and the “callee.” Whenever the callee is ready to accept a request, it asserts its rdy signal. In this lab, we will be using a slightly more sophisticated ready/enable microprotocol to achieve the same goal. In some of the previous labs, you used a simple start/done microprotocol to let your circuit take a variable number of cycles. The following diagram shows the values of key, key, and key for the 24-bit secret key of 'b000000110101111100111100 = 'h035F3C. The length of the secret key can vary - in this lab, we will use a smaller key of 24 bits (3 bytes) to ensure that you can “crack” the encryption in a reasonable amount of time. Plaintext = pad xor ciphertext - xor each byte pseudo-random generation algorithm: generate byte stream (“pad”) to be xor'd with the ciphertext
#Cracker bus simulator 18 mod
J = (j + s + key) mod 256 - for us, keylength is 3 key-scheduling algorithm: initialize the s array The basic ARC4 algorithm uses the following parameters: ParameterĪrray of bytes that represent the secret key (24 bits in our implementation)Īrray of bytes that represent the encrypted messageĪrray of bytes that represent the decrypted result (same length as ciphertext)Īnd proceeds as shown in this pseudocode: Because xor is symmetric, encryption and decryption are exactly the same. A stream cipher like ARC4 uses the provided encryption key to generate a pseudo-random byte stream that is xor'd with the plaintext to obtain the ciphertext. You don't have to do this, of course, and you will not be marked on it, but it will make your life much easier. More than prior labs, this one would benefit from having a “known good” high-level implementation that you can compare with step by step.
#Cracker bus simulator 18 code
Do not be discouraged by this - the amount of actual code you have to write is not excessive.įinally, some debugging advice.
#Cracker bus simulator 18 how to
The description of this lab is fairly long, but this is mostly because it includes lots of explanations about ARC4, how to generate and examine memories, and so on. Finally, you will create a cracking circuit with multiple decryption units to speed things up. Next, you will extend this to build an ARC4 cracking circuit the circuit will implement a “brute-force” attack by cycling through the entire key space and stopping when a successful decryption is performed. The secret key will initially be obtained from a bank of switches on your DE1-SoC board, and the encrypted message will be given to you as a ROM initialization file. In the rest of the lab, you will first design an ARC4 decryption circuit. Still, the structure of ARC4 is similar to modern symmetric encryption methods, and provides a good vehicle for studying digital circuits that make extensive use of on-chip memory. ARC4 is a popular symmetric stream cipher, and was widely used in encrypting web traffic, wireless data, and so on it has since been broken. The circuit you will create is an ARC4 decryption circuit. In this lab, you will get experience creating a design that contains several on-chip memories, and uses a more efficient ready-enable interface to connect modules that have variable latencies. Task 3: The Pseudo-Random Generation Algorithm.Examining memory contents inside the FPGA.Implementing the S-array initialization step.Task 1: Embedded memories and ARC4 state initialization.
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