Domain 3B: Cryptography Flashcards
What is crypography?
Cryptography is secret writing, a type of secure communication understood by the sender and intended recipient only.
What is cryptology?
Cryptology is the science of secure communications. Cryptography creates messages with hidden meaning; cryptanalysis is the science of breaking those encrypted messages to recover their meaning.
What is a cipher?
A cipher is a cryptographic algorithm. A plaintext is an unencrypted message. Encryption converts a plaintext to a ciphertext. Decryption turns a ciphertext back into a plaintext.
What is confusion?
Confusion is the relationship between the plaintext and ciphertext; it should be as random (confusing) as possible
What is diffusion?
Diffusion means the order of the plaintext should be “diffused” or dispersed in the ciphertext. Confusion means that the relationship between the plaintext and ciphertext should be as confused or random as possible.
What is permutation?
Permutation (transposition) provides confusion by rearranging the characters of the plaintext
What is the difference between asymmetric encryption, symmetric encryption, and hybrid encryption?
Asymmetric
Pros: It does not need a pre-shared key, only 2x users = total keys.
Cons: It is much slower, it is weaker per bit.
Symmetric:
Pros: Much faster, stronger per bit.
Cons: Needs a pre-shared key, n(n-1)/2 users, becomes unmanageable with many users.
Hybrid Encryption:
Uses Asymmetric encryption to share a Symmetric Key (session key).
We use the security over an unsecure media from Asymmetric for the initial exchange and we use the speed and higher security of the Symmetric for the
actual data transfer.
The Asymmetric Encryption may send a new session key every so often to ensure security.
How does symmetric encryption work?
Symmetric encryption uses a single key to encrypt and decrypt. If you encrypt a zip file, then decrypt with the same key, you are using symmetric encryption. Symmetric encryption is also called “secret key” encryption because the key must be kept secret from third parties. Strengths of this method include speed and cryptographic strengthning bit of key; however, the major weakness is that the key must be securely shared before two parties may communicate securely
What is DES?
DES is the data encryption standard, which describes the data encryption algorithm (DEA). IBM designed DES, based on their older Lucifer symmetric cipher, which uses a 64-bit block size (ie, it encrypts 64 bits each round) and a 56-bit key.
What is triple DES?
Triple DES applies single DES encryption three times per block. Formally called the “triple data encryption algorithm (TDEA) and commonly called TDES,” it became a recommended standard in 1999.
What is AES?
The advanced encryption standard (AES) is the current US standard in symmetric block ciphers. AES uses 128-bit (with 10 rounds of encryption), 192-bit (with 12 rounds of encryption), or 256-bit (with 14 rounds of encryption) keys to encrypt 128-bit blocks of data.
How does asymmetric encryption work?
Asymmetric encryption uses two keys, one for encryption and the other for decryption. The public key, as its name indicates, is made public, and asymmetric encryption is also called public key encryption for this reason. Anyone who wants to communicate with you may simply download your posted public key and use it to encrypt their plaintext. Once encrypted, your public key cannot decrypt the plaintext, but your private key can do so. As the name implies, your private key must be kept private and secure.
What is the purpose of a key agreement?
Key agreement allows two parties the security with which to agree on a symmetric key via a public channel, such as the Internet, with no prior key exchange. An attacker who is able to sniff the entire conversation is unable to derive the exchanged key. Whitfield Diffie and Martin Hellman created the Diffie-Hellman Key Agreement Protocol (also called the Diffie-Hellman Key Exchange) in 1976. Diffie-Hellman uses discrete logarithms to provide security.
How does ECC work? Why is it used?
ECC leverages a one-way function that uses discrete logarithms as applied to elliptic curves. Solving this problem is harder than solving discrete logarithms, so algorithms based on elliptic curve cryptography (ECC) are much stronger per bit than systems using discrete logarithms (and also stronger than factoring prime numbers). ECC requires less computational resources because it uses shorter keys comparison to other asymmetric methods. Lower-power devices often use ECC for this reason.
What is the purpose of hashing?
Hash functions are primarily used to provide integrity: if the hash of a plaintext changes, the plaintext itself has changed. Common older hash functions include secure hash algorithm 1 (SHA-1), which creates a 160-bit hash and Message Digest 5 (MD5), which creates a 128-bit hash. There are weaknesses in both MD5 and SHA-1, so newer alternatives such as SHA-2 are recommended.
Why are hashes not unique like their plaintext counterparts?
Hashes are not unique because the number of possible plaintexts is far larger than the number of possible hashes
What is it called when more than one document has the same hash?
More than one document could have the same hash’. This is called a collision.
What is the purpose of differential cryptanalysis?
Differential cryptanalysis seeks to find the difference between related plaintexts that are encrypted. The plaintexts may differ by a few bits. It launches as an adaptive chosen plaintext attack; the attacker chooses the plaintext to be encrypted though he or she does not know the key and then encrypts related plaintexts
What is the purpose of linear crypanalysis?
Linear cryptanalysis is a known plaintext attack where the cryptanalyst finds large amounts of plaintext/ciphertext pairs created with the same key. The pairs are studied to derive information about the key used to create them. Both differential and linear analysis can be combined as differential linear analysis.
What is a side channel attack?
Side-channel attacks use physical data to break a cryptosystem, such as monitoring CPU cycles or power consumption used while encrypting or decrypting
What is the purpose of digital signatures?
Digital signatures are used to cryptographically sign documents. Digital signatures provide nonrepudiation, which includes authentication of the identity of the signer, and proof of the document’s integrity (proving the document did not change). This means the sender cannot later deny or repudiate signing the document.
