Data Encryption Standard (DES) Flashcards
Block Cipher Size?
64-bit
Key Size?
56-bit
How does it work?
Long series of XOR operations
How many rounds?
16
Electronic Codebook Mode
Each time the algorithm processes a 64-bit block, it simply encrypts the block using the chosen secret key.
ECB Mode weakness?
If the algorithm encounters the same block multiple times it will produce the same encrypted block.
If an enemy were eavesdropping on the communications, they could simply build a “code book” of all the possible encrypted values.
Cipher Block Chaining Mode
Each block of unencrypted text is XORed with the block of ciphertext immediately preceding it before it is encrypted using the DES algorithm.
CBC Mode weakness?
If one block is corrupted during transmission it becomes impossible to decrypt.
Cipher Feedback Mode
Streaming cipher version of CBC.
CFB operates against data produced in real time. Uses memory buffers of the same same block size. As the buffer becomes full, it is encrypted and then sent to the recipients.
CFB Mode weakness
If one block is corrupted during transmission it becomes impossible to decrypt.
Output Feedback Mode
Operates in almost the same fashion as it does in CFB mode.
Instead of XORing an encrypted version of the previous block of ciphertext, DES XORs the plaintext with a seed value. Future seed values are derived by running the DES algorithm on the previous seed value.
Advantage of OFB mode?
There is no chaining and transmission errors do not propagate.
Counter Mode
Uses a stream cipher similar to that used in CFB and OFB modes.
Creates a seed value for each encryption/decryption operations from the results of the previous seed values, it uses a simple counter that increments for each operation.
Advantage of Counter mode?
Errors to do not propagate
Triple DES Modes?
DES-EEE3
DES-EEE2
DES-EDE2
DES-EEE3
Encrypts the plaintext three times
Has an effective key length of 168 bits
DES-EDE2
Uses three keys but replaces the second encryption operation with a decryption operation.
DES-EEE2
Uses only two keys.
Advanced Encryption Standard
Standard only allows the processing of 128-bit blocks.
Rinjdael exceeded the specification.
128, 192, and 256
International Data Encryption Algorithm (IDEA) block size?
64-bit
International Data Encryption Algorithm (IDEA) key size?
128-bit key broken in a series of operations into 52 16-bit subkeys.
Blowfish block size?
64-bit
Blowfish key sizes?
32 through 448
Twofish block size?
128-bit
Twofish key sizes?
128 through 256
Diffie-Hellman Key Agreement Protocol
Allows two parties to securely agree on a symmetric key via a public channel, such as the Internet, with no prior key exchange.
Uses discrete logarithms to provide security.
Elliptic Curve Cryptography (ECC)
ECC leverages a one-way function that uses discrete logarithms as applied to elliptic curves.
Asymmetric vs. Symmetric
Asymmetric is much slower than symmetric encryption, and is also weaker per bit of key length.
Hash Functions
Provides encryption using an algorithm and no key. They are called “one-way hash functions” because there is no way to reverse encryption.
MD5
Created by Ronald Rivest
Creates a 128-bit hash value.
MD6 is the newest version.
SHA-1
160-bit hash value
SHA-2
SHA-224, SHA-256, SHA-384, and SHA-512
HAVAL
Hash of Variable Length – is a hash algorithm that creates message digests of 128, 160, 192, 224, or 256 bits in length, using 3, 4, or 5 rounds.
Uses some of the design principles behind the MD family of hash algorithms, and is faster than MD5.
