Module 15 Flashcards
To ensure secure communications across both the public and private infrastructure, the network
administrator’s first goal is to
secure the network
infrastructure, including routers, switches, servers, and hosts.
There are three primary objectives of securing
communications:
- Authentication
- Integrity
- Confidentiality
Authentication
There are two primary methods for validating a source in network communications:
authentication services and
data nonrepudiation services.
In network communications, authentication can be accomplished using
cryptographic methods.
is a similar service that allows the sender of a message to be uniquely
identified.
Data nonrepudiation
With nonrepudiation services in place, a sender cannot deny having been the source
of that message.
ensures that messages are not altered in transit. With___, the receiver can verify that the received message is identical to the sent message and that no manipulation occurred.
Data integrity
ensures privacy so that only the receiver can read the message. This can be achieved through encryption.
Data confidentiality
is the process of scrambling data so that it cannot
be easily read by unauthorized parties.
Encryption
When enabling encryption, readable data is called ____ while the encrypted
version is called __.
readable data = plaintext, or cleartext,
encrypted version = encrypted text or ciphertext
The plaintext readable message is converted to
ciphertext, which is the unreadable, disguised message.
reverses the process of encryption
Decryption
A __ is required to encrypt and decrypt a message. The ___ is the link between the plaintext
and ciphertext.
key
Using a ____ is another way to ensure data confidentiality. A____ transforms
a string of characters into a usually shorter, fixed-length value or key that represents the
original string.
hash function
The difference between hashing and encryption is
in how the data is stored.
The ___ was an electromechanical
encryption device that was developed and used by Nazi Germany during World War II. The device depended on the distribution of pre-shared keys that were used to encrypt and decrypt messages.
Enigma machine
depended on the distribution of pre-shared keys that were used to encrypt and decrypt messages.
Enigma machine
In ____, no letters are replaced; they are simply rearranged.
transposition ciphers
Another example of a transposition cipher is known as the ____. They are staggered, some in front, some in the middle and some in back, across several parallel lines.
rail fence cipher
Modern encryption block cipher algorithms, such as ____, still use transposition as part of the algorithm.
AES and the legacy 3DES,
____ substitute one letter for another. In their simplest form, ____ retain the letter frequency of the original message.
Substitution ciphers
The ____ is based
on the Caesar cipher, except
that it encrypts text by using a
different polyalphabetic key
shift for every plaintext letter.
The different key shift is
identified using a shared key
between sender and receiver.
Vigenère cipher
__ was an AT&T Bell Labs engineer who, in 1917, invented, and later patented, the stream cipher. He also co-invented the one-time pad cipher.
Gilbert Vernam
Vernam proposed a teletype cipher in which a prepared key consisting of an arbitrarily long, non-repeating sequence of numbers was
kept on paper tape. It was then combined character by character with the plaintext message to produce the ciphertext.
To decipher the ciphertext, the same paper tape key was again combined character by character, producing the plaintext. Each tape was used only once; hence, the name one-time pad. Several difficulties are inherent in using onetime pads in the real world.
one-time pad ciphers
the stream cipher
is the practice and study of determining the meaning of encrypted information
(cracking the code), without access to the shared secret key. This is also known as
Cryptanalysis or codebreaking.
Throughout history, there have been many instances of cryptanalysis:
- The Vigenère cipher had been absolutely secure until it was broken in the 19th century by English cryptographer Charles Babbage.
- Mary, Queen of Scots, was plotting to overthrow Queen Elizabeth I from the throne and sent encrypted messages to her co-conspirators. The cracking of the code used in this plot led to the beheading of Mary in 1587.
- The Enigma-encrypted communications were used by the Germans to navigate and direct their U-boats in the Atlantic. Polish and British cryptanalysts broke the German Enigma code. Winston Churchill was of the opinion that it was a turning point in WWII.
Methods of Cracking Code
Several methods are used in cryptanalysis:
- Brute-force method
- Ciphertext method
- Known-Plaintext method
- Chosen-Plaintext method
- Chosen-Ciphertext method
- Meet-in-the-Middle method
- The attacker tries every possible key knowing that eventually one of them will work.
- Brute-force method
- The attacker has the ciphertext of several encrypted messages but no knowledge of the underlying plaintext.
- Ciphertext method
- The attacker has access to the ciphertext of several messages and knows something about the plaintext underlying that ciphertext.
- Known-Plaintext method
- The attacker chooses which data the encryption device encrypts and observes the ciphertext output.
- Chosen-Plaintext method
- The attacker can choose different ciphertext to be decrypted and has access to the decrypted plaintext.
- Chosen-Ciphertext method
- The attacker knows a portion of the plaintext and the corresponding ciphertext.
- Meet-in-the-Middle method
