Chapter 7 - Cryptography Flashcards
Unencrypted information
information in an understandable form, either cleartext or plaintext
Plaintext
unencrypted text that gets encrypted and becomes ciphertext
Cleartext
any unencrypted data
Encrypted information
information in scrambled form (ciphertext)
Ciphertext
Encrypted text that becomes plaintext when decrypted
Algorithm
A repeatable process that produces the same result when the same input is received
Open-source ciphers
Make it possible for experts around the world to examine ciphers for weaknesses
Transposition ciphers
rearrange characters or bits of data
Substitution ciphers
replace bits, characters, or blocks of information with something different
Data encryption standard
A symmetric key algorithm that encrypts using a 56-bit key
DES was…
once widely used but now considered outdated and easy to crack
What is the goal of cryptography?
To make the cost or time required to access encrypted information exceed the value of the protected info
Quantum Cryptography
a new form of cryptography that uses photons, particles, and waves of light,
How does cryptography play a role in the three tenets of cybersecurity?
Confidentiality - keeps information hidden from unauthorized users
Integrity - ensures that no one changes information after transmitting it
Availability - ensures info is only available to those that should have access to it
Nonrepudiation
a principle ensuring that a party cannot deny having performed a specific action, like signing a document or sending a message
Conditions for nonrepudiation
- An effective asymmetric key algorithm
- A strong hash function
- A means to produce a digital signature
Symmetric key ciphers
use the same key to encrypt and decrypt
Asymmetric key ciphers
use different keys to encrypt and decrypt
Two ways to break a cipher
- Analyze the ciphertext to find the plaintext or key
- Analyze the ciphertext and its associated plaintext to find the key
Ciphertext-only attack (COA)
the ciphertext sample is available but not the plaintext
Known-plaintext attack (KPA)
the ciphertext and associated plaintext are available
Key
a value that is an input to a cryptosystem
Keyspace
the number of possible keys to a cipher
Key management is…
one of the most difficult and critical parts of the cryptosystem
Rather than each organization creating the infrastructure to manage its own keys, hosts may…
agree to trust a common key-distribution center (KDC)
Checksum
summary information appended to a message to ensure that the values of the message have not changed
Hash Functions
compute a checksum of a message and combine it with a cryptographic function so that the result is tamperproof
Characteristics of hash functions
- Not reversible
- Useful for protecting data from unauthorized change
- designed in a way that no one can forge a message that will result in the same hash as the
Digital signatures
bind the identity of an entity to a particular message or piece of information
Characteristics of digital signatures
- Ensure the integrity of a message and verify who wrote it
- Require asymmetric key cryptography
- Plaintext + hash algorithm + private key = digital signature
Asymmetric keys…
Do not require each party to first share a secret key
Key directory
A trusted repository of all public keys
Key escrow
A key storage method that allows some authorized third-party access to a key under certain circumstances
