An authentication method that periodically re-authenticates the client by establishing a hash that is then resent from the client is called ______.
CHAP
https://en.wikipedia.org/wiki/Challenge-Handshake_Authentication_Protocol
Challenge-Handshake Authentication Protocol (CHAP) is an identity verification protocol that does not rely on sending a shared secret between the access-requesting party and the identity-verifying party (the authenticator). CHAP is based on a shared secret, but in order to authenticate, the authenticator sends a ''challenge'' message to the access-requesting party, which responds with a value calculated using a ''one-way hash'' function that takes as inputs the challenge and the shared secret. The authenticator checks the response against its own calculation of the expected hash value. If the values match, the authentication succeeds, otherwise it fails. Following the establishment of an authenticated connection, the authenticator may send a challenge to the access-requesting party at random intervals, to which the access-requesting party will have to produce the correct response.
Incorrect answers:
EAP - A framework that allows for creation of different ways to provide authentication, such as smart cards
SPAP - Shiva Password Authentication Protocol, PAP with encryption for the usernames/passwords that are transmitted.
PAP - Password Authentication Protocol. Used to authenticate users, but is no longer used because the information was sent in cleartext.
In a Feistel cipher, the two halves of the block are swapped in each round. What does this provide?
Confusion
https://en.wikipedia.org/wiki/Confusion_and_diffusion#Definition
Confusion means that each binary digit (bit) of the ciphertext should depend on several parts of the key, obscuring the connections between the two.
The property of confusion hides the relationship between the ciphertext and the key.
This property makes it difficult to find the key from the ciphertext and if a single bit in a key is changed, the calculation of the values of most or all of the bits in the ciphertext will be affected.
Confusion increases the ambiguity of ciphertext and it is used by both block and stream ciphers.
Incorrect answer:
Avalanche - The avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip). In the case of high-quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext. The actual term was first used by Horst Feistel, although the concept dates back to at least Shannon's diffusion.
Diffusion - Diffusion means that if we change a single bit of the plaintext, then (statistically) half of the bits in the ciphertext should change, and similarly, if we change one bit of the ciphertext, then approximately one half of the plaintext bits should change.[2] Since a bit can have only two states, when they are all re-evaluated and changed from one seemingly random position to another, half of the bits will have changed state.
Substitution - Substitution technique is a classical encryption technique where the characters present in the original message are replaced by the other characters or numbers or by symbols.
A symmetric Stream Cipher published by the German engineering firm Seimans in 1993. A software based stream cipher that uses a Lagged Fibonacci generator along with concepts borrowed from shrinking generator ciphers.
FISH
https://en.wikipedia.org/wiki/FISH_(cipher)
The FISH (FIbonacci SHrinking) stream cipher is a fast software based stream cipher using Lagged Fibonacci generators, plus a concept from the shrinking generator cipher. It was published by Siemens in 1993. FISH is quite fast in software and has a huge key length. However, in the same paper where he proposed Pike, Ross Anderson showed that FISH can be broken with just a few thousand bits of known plaintext.
Incorrect answers:
Twofish - symmetric algorithm. Designed by Bruce Schneier, John Kelsey, Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson. Uses a block size of 128 bits and key sizes of 128, 192, or 256 bits. It is a Feistel cipher.
IDEA - symmetric algorithm. Designed by James Massey and Xuejia Lai. Operates on 64 bit blocks and has a 128 bit key. Consists of 8 identical transformations each round and an output transformation.
DESX - symmetric algorithm. 64 bit key is appended to data, XOR it, and then apply the DES algorithm.
If Bob is using asymmetric cryptography and wants to send a message to Alice so that only she can decrypt it, what key should he use to encrypt the message?
Alice's public key
https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange
In asymmetric (public key) cryptography, both communicating parties (i.e. both Alice and Bob) have two keys of their own --- just to be clear, that's four keys total. Each party has their own public key, which they share with the world, and their own private key which they ... well, which they keep private, of course but, more than that, which they keep as a closely guarded secret. The magic of public key cryptography is that a message encrypted with the public key can only be decrypted with the private key. Alice will encrypt her message with Bob's public key, and even though Eve knows she used Bob's public key, and even though Eve knows Bob's public key herself, she is unable to decrypt the message. Only Bob, using his secret key, can decrypt the message ... assuming he's kept it secret, of course.
