The act of making something difficult to understand.

Substitution Cipher - Substitutes one symbol for another.

Example: ROT13 (rotate 13 places)

**XOR (eXclusive OR)**- a logical operation that outputs true only when inputs differ (one is true, the other is false).

*Data Encryption Standard (DES)*Adopted by NIST in 1977.

Block cipher using 64-bit blocks (56-bit key + 8 bits of parity).

Short key length subject to brute-force attacks.

*3DES (Triple DES)*DES algorithm computed three times.

Using a 'key bundle' three different DES keys, each of 56 bits = total bit strength of 168 bits (known as 3TDEA).

Also options to reuse keys.

Uses 48 rounds of computation.

Offers high resistance to differential cryptana

*Advanced Encryption Standard (AES)*Original name 'Rijndael"

Free for any use public or private, commercial or non-commercial.

Adopted by NIST in 2001.

Block cipher with 128 block size.

Three key lengths: 128, 192, and 256.

It uses multiple encryption rounds to reach these key lengths:

10 rounds for 128-bit

12 rounds for 192-bit

14 rounds for 256-bit

*RC4 / RC5 / RC6 - Rivest Cipher*RC4 - Stream Cipher

RC5/6 - Block Ciphers

Works with key sizes between 40 and 2048 bits.

*Blowfish / Twofish*A symmetric block cipher that can use variable-length keys from 32 bits to 447 bits.

Twofish uses 128-bit blocks.

*International Data Encryption Algorithm (IDEA)*128-bit key

Similar to DES, but more secure due to having a longer key.

Used in PGP.

*One-Time Pad (OTP)*Most secure crypto implementation.

Use of a key as long as the plain-text message.

Only used once, then destroyed.

*Skipjack*NSA developed block cipher used in clipper chip.

Uses an 80-bit key to encrypt 64-bit blocks of data.

*GOST*A Soviet and Russian government standard symmetric key block cipher.

Block size of 64 bits.

Developed to counter Data Encryption Standard (DES).

*Psuedo Random Number Generator (PRNG)*A type of algorithm that generates a number that is "random enough" for cryptographic purposes.

Used in AES, DES, and Blowfish.

*Counter Mode (CTR)*Turns a block cipher into a stream cipher.

Used to generate a keystream.

Each block combines a nonce or IV with a sequentially assigned number to produce a unique counter block that is then encrypted.

*Cipher-Block Chaining (CBC)*Uses an IV with the first block.

Thereafter, each block of plain text is obfuscated with the cipher text from the previous block before it is encrypted.

Introduces more diffusion & reduces effects of plain-text attacks.

*Electronic Code Book (ECB)*The easiest method.

Direct encryption of each block of input plaintext.

Output is in form of blocks of encrypted ciphertext.

*Cipher Feedback Mode (CFB)*Uses an initial chaining vector (ICV) in its processing.

Performs cipher feedback encryption.

Operates on segments instead of blocks.

*Galois/Counter Mode*Used with symmetric-key key block ciphers.

An authentication encryption designed to give both integrity and confidentiality.

Used with 128 bit block ciphers.

Uses two keys.

One for encryption.

One for decryption.

Keys are mathematically related.

Public / Private key encryption.

Only the private key needs to be kept secret.

Only the private key can decrypt the message.

Extra computational overhead.

Used primarily for:

Secure exchange of shared keys for symmetric encryption.

Digital signatures.

Solves the issue of key exchange with symmetric encryption.

*Rivest, Shamir, and Adleman (RSA)*Used for key exchange and digital signatures.

Key can be any length.

Algorithm works by multiplying two large prime numbers.

Derives two different numbers: one public key and one private key.

*Diffie-Hellman Key Exchange (D-H)*Two parties, without prior arrangement, can agree on a secret key that is known only to them.

Only used to generate a shared key (not encryption).

Key can be safely & secretly shared on a public network.

*Diffie-Hellman Ephemeral (DHE)*Uses a different key for every conversation.

Supports perfect forward secrecy.

*Elliptical Curve Cryptography (ECC)*Technique using elliptical curves to calculate simple but difficult-to-break encryption keys.

Uses smaller key sizes to obtain the same level of security (160-bit ECC = 1024-bit RSA).

Requires fewer resources than RSA.

*Elliptical Curve Diffie-Hellman Ephemeral (ECDHE)*Variant of DHE using ECC for perfect forward secrecy.

*El Gamal*An extension to the Diffie-Hellman using an ephemeral key.

*Pretty Good Privacy (PGP) and GNU Privacy Guard (GPG)*Developed by Phillip R. Zimmerman in 1991.

Used to encrypt and sign email messages.

Establishes a web of trust between the users.

A web of trust implies that the users generate and distribute their public keys.

These keys are signed by users for each other, establishing a community of users who trust each other for communication.

Every user has a collection of signed public keys stored in a file known as a web ring.

PGP provides the following functionalities:

Confidentiality through the International Data Encryption Algorithm (IDEA).

Integrity through the Message Digest 5 (MD5) hashing algorithm.

Authentication through public key certificates.

Non-repudiation through encrypted signed messages.

*Knapsack*{source}â€‹AKA Merkle-Hellman Knapsack Crypotosystem

One of the earliest public key cryptosystems.

'Digital fingerprint'

Work by taking a string of any length and producing a fixed-length string for output.

Changing the original changes the hash value.

Originator takes a hash of the file and provides hash to receiver.

Receiver takes hash of file and compares with original to ensure file integrity.

*Secure Hash Algorithm (SHA, SHA-1, SHA-2, SHA-3)*Developed by the US NSA

SHA-1 can generate a 160-bit hash from any variable-length string of data.

SHA-2 = SHA-22, SHA-256, SHA-348, and SHA-512 (based on their digest lengths)

SHA-3, published in 2012, not widely used yet.

*Message Digest Algorithm (MD2, MD4, MD5)*The most widely known hashing function.

Produces a 16-byte hash value, usually expressed as a 32 digit hexadecimal number.

Considered compromised. Rainbow tables have been published which allow people to reverse MD5 hashes made without good salts.

*Message Authentication Code (MAC)*Authentication of messages using a secret key.

Used in electronic fund transfers to protect against fraud.

*Hash-Based Message Authentication Code (HMAC)*HMAC combines a cryptographic hash function and a secret crypto key.

HMAC does not encrypt the message, only the key.

*Keyed Hashing for Message Authentication Code (KHMAC)*Used to digitally sign packets that are transmitted on Internet Protocol Security (IPSec) connections.

*RACE Integrity Primitives Evaluation Message Digest (RIPEMD)*Design based on MD4.

160-bit version of the algorithm (RIPEMD-160) performs comparably to SHA-1.

*HAVAL*Processes 1024-bit block sizes of information.

Creates message digests of variable sizes rather than a fixed output value.

Produces hashes in lengths of 128, 160, 192, 224, and 256.

*Rainbow Table*A pre-computed table for reversing cryptographic hash functions.

All of the possible hashes are computed in advance.

*Salt*Random data that is used as an additional input to hash

Processes used to take a weak key and make it stronger, usually by making it longer.

*Bcrypt*Based on the blowfish algorithm.

Provides an adaptive hash function based on a key factor.

*Password-Based Key Derivation Function 2 (PBKDF2)*Algorithm applies a pseudo-random function to the password combined with a salt of at least 64 bits, and then repeats the process at least 1000 times.

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