Week 2 - Symmetric Encryption Flashcards
What is cryptography?
general idea
General idea that describes the practice of coding and hiding messages from potential enemies (been around for thousands of years)
What is encryption?
the action of taking a plaintext message + apply a cipher to it = ciphertext, garbled unreadable text
What are 2 components a cipher is made out of?
- the encryption algorithm
- the key
What’s an encryption algorithm?
the processes that convert the plaintext into ciphertext
What is the key when it comes to the cipher operation?
it introduces something unique into your cipher so anyone using the same algorithm can’t decode the message
What does security through obscurity mean?
basically that if no one knows what algorithm we’re using, we’re safe from attackers
What is a cryptosystem?
Even if the enemy knows your exact encryption algorithm, they’re still unable to recover the plaintext from an intercepted ciphertext
What is cryptanalysis?
looking for hidden messages, trying to decipher coded messages
Frequency analysis is the practice of studying what?
studying the frequency with which letters appear in ciphertext
What was the first programmable digital computer developed during WWII to aid in the use of automation technology to apply to cryptanalysis?
Colossus
What is steganography the practice of?
the practice of hiding information from 3rd parties but not encoding it
What’s an example of steganography?
Writing a letter with invisible ink, must be made visible using a mechanism known to the recipient
(no decoding necessary)
What are some modern steganography techniques?
embedding messages or files into other files (images, videos) that can be extracted using steganography software
What is a symmetric key algorithm? Why is it called symmetic? (1)
These are called symmetric because they use the same key to encrypt and decrypt a message
What is a substitution cipher?
an encryption mechanism that replaces parts of the plaintext with ciphertext
(like when you substitute certain letters for other letters in a message)
What is the ROT13 substitution cipher?
you rotate the alphabet (in order) 13 places
For example, A would become N
(this is also an example of a Caesar Cipher)
What’s a Caesar Cipher?
substitution using the alphabet, usually by shifting or rotating it
ROT13 is a ___ Cipher that uses a key of ____
ROT13 is a Caesar Cipher that uses a key of 13
What’s a stream cipher?
1 to 1 input/output encryption of a digit or character
(takes 1, encrypts 1 in and out)
How does a block cipher encode data?
Places data into a bucket/block of a fixed size, encodes entire block as 1 unit
Which symmetric ciphers are faster and less complex but may be less secure: stream or cipher?
Stream ciphers
(if the same key is used to encrypt data 2+ times, it’s possible to break the cipher and recover plaintext)
What does a key size comprise of? (defined in bits/data)
the total number of bits/data that comprises the encryption key
Key size is the upper limit for the total possible keys for a given ___ ____
encrypted algorithm
What symmetric block cipher replaced DES?
AES (Advanced Encryption Standard)
What’s the difference between AES and DES symmetric encryption? (2)
AES:
- uses 128-bit blocks (2x the size of DES 64-bit)
- supports key lengths of 128, 192, or 256-bit
Are brute force attacks possible on AES encryption standards today?
No, because of the large key size and computing power/time required those attacks are only theoretical right now
What popular algorithm was dropped due to its weakness and vulnerabilities?
RC4 (Rivest Cipher 4), a symmetric stream cipher
(used in WEP, WPA, SSL, TLS)
Web browsers dropped support for RC4 along with all versions of SSL and adopted what instead?
TLS
