P2 T1 L12 - Encryption Flashcards
Define encryption (1 point)
- A way of making sure data cannot be understood if you don’t possess the means to decrypt it.
Plaintext of a message sent is encrypted using a _______ _________ and ____ into equivalent ciphertext.
When received, the ciphertext is decrypted back to plaintext using the same or different ____.
Two methods at the opposite end of the security spectrum are the ______ cipher (low security) and the _______ cipher (high security).
cipher algorithm
key
key
Caesar
Vernam
Give 3 uses of encryption
- Sometimes used to store passwords.
- Used for sending data over a network securely.
- Making storage media secure, particularly portable media.
(Caesar cipher)
The Caesar cipher is most basic type of encryption and the most insecure
Letters of the alphabet are shifted by a __________ _________.
_________ is data in human-readable form.
___________ is data that has been encrypted.
consistent amount
Plaintext
Ciphertext
(Vernam cipher)
The encryption key, also known as the ___-____ ____, is the only cipher proven to be unbreakable
The key must be: (2 points)
one-time pad
- A truly random sequence greater or equal in length than the plaintext and only ever used once.
- Shared with the recipient by hand, independently of the message and destroyed immediately after use.
(The one-time pad)
The one-time pad must be truly _________, generated from a _________ and __________ phenomenon.
Sources may include: (Give 4 examples)
A truly random key will render any frequency analysis useless as it would have a _________ ___________.
Computer generated ‘random’ sequences are not actually random.
random
physical
unpredictable
- Atmospheric noise
- Radioactive decay
- Movements of a mouse
- Snapshots of a lava lamp
uniform distribution
(Different types of encryption)
Explain Symmetric methods (3 points)
- Also known as private-key cryptography,
- the key used to encrypt and decrypt the message must remain secure, because anyone with access to it can decrypt the data.
- Using this method, a sender encrypts the data with one key, sends the data (the ciphertext) and then the receiver uses the key to decrypt the data.
(Different types of encryption)
Explain Asymmetric methods (3 points)
- Also known as public-key cryptography
- it uses two keys for encryption or decryption (it has the potential to be more secure as such).
- a public key is freely available to everyone and is used to encrypt messages, and a different, private key is used by the recipient to decrypt messages.
Hashing is NOT encryption.
Hashing can only be done one ____.
Using hashing for password protection:
- Password stored as ________ ______ (so, not plaintext)
- Login software _________, and looks for a match (or not)
- Gives appropriate message
way
hashed value
rehashes
How are most codes cracked? (name 5 ways)
- Substitution (commonly used)
- Transposition (commonly used)
- Reverse engineering
- Dictionary attacks
- Brute force
Explain dictionary attacks (1 point)
- After each attempt, the result is compared with the dictionary
Explain brute force (in code cracking) (1 point)
- Looking at every single permutation and combination to see if it compares to the decrypted text.
(Frequency analysis)
______ are not used equally often.
In English, E is by far the most common letter, followed by T, A, O, I, N, S, R, then H.
Other letters like Z, J, K, Q, X are fairly rare.
In Czech, the letter Z is only worth 4 points in Scrabble! It’s worth 10 in the English version.
Letters
What makes for a strong encryption? (2 points)
- No pattern matching can be done (repeated letters, vowels)
- There are enough possible values that it is hard to guess
Hash functions are ____-____ ________. This means that given the hash value it is not possible to regenerate the key that the hash function acted upon, but given the hash key it is possible to generate its hash value.
This is exploited in password protection.
one-way functions
