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?
(Rotate13, “rotate by 13 places”, sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the Latin alphabet.
What’s a Caesar Cipher?
simple encryption technique that involves replacing letters in a message with other letters or symbols by shifting them a fixed number of positions in the alphabet
ROT13 is a ___ Cipher that uses a key of ____
ROT13 is a substitution cipher that uses a key of 13.
What’s a stream cipher?
a cryptographic algorithm that encrypts and decrypts data in a continuous stream, one bit or byte at a time
How does a block cipher encode data?
by breaking it into fixed-size blocks(128/64bits) and using a secret key to transform each block into ciphertext
Which symmetric ciphers are faster and less complex but may be less secure: stream or cipher?
stream ciphers
What does a key size comprise of? (defined in bits/data)
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Key size is the upper limit for the total possible keys for a given ___ ____
cryptographic algorithm
What symmetric block cipher replaced DES?
Advanced Encryption Standard (AES)
What’s the difference between AES and DES symmetric encryption? (2)
AES: Uses a key size of 128, 192, or 256 bits. Harder to crack.
DES: Uses a 56-bit key size
Are brute force attacks possible on AES encryption standards today?
AES-256 encryption is considered virtually uncrackable using brute force methods
What popular algorithm was dropped due to its weakness and vulnerabilities?
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Web browsers dropped support for RC4 along with all versions of SSL and adopted what instead?
TLS 1.3 and other algorithms like AES and 3DES
