Cissp - Crytography

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Cryptography Notation

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name-w/r/b
example:
RC5-32/12/16

w=Word Size (bits), r=Rounds, b=Bytes (x4=bits)

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DES - Name

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Data Encryption Standard

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DES - Algorithm

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DEA - Data Encryption Algorithm (altered form of Lucifer)
Symmetric
64/16/56

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Lucifer

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Chosen for DES and renamed DEA

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DES - Modes

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ECB - Code Book, No Chaining
CBC - Block Chaining
CFB - Cipher Feedback
OFB - Output Feedback
CTR - Counter

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3DES - Name

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Triple Data Encryption Algorithm

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3DES - Algorithm

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Triple DEA
Symmetric
64/48/56

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3DES - Modes

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EEE3
EDE3
EEE2
EDE2
E = Encryption, D = Decryption
Decryption during Encryption uses a different key

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3DES - Why was it developed

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Quick fix of DES before AES was ready

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AES - Name

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Advanced Encryption Standard

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AES - Algorithm

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Rijndael
Symmetric
128/10/32
192/12/48
256/14/64

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IDEA - Name

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International Data Encryption Algorithm

Patented

Used by PGP

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IDEA - Algorithm

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Symmetric
64bit / 16
128 key

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Blowfish

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Symmetric
64/16/32-448 bit

Public Domain

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RC4

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Symmetric
Stream
Improperly used in Wireless and will be replaced with 802.11i
Proprietary but source published under name ARC4

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RC5

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Symmetric
Block
32,64,128/1-255/1-2048

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RC6

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Symmetric
Block
Improved upon RC5 - speed increase
32,64,128/1-255/1-2048

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Symmetric Strengths / Asymmetric Strengths

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Symmetric:
Much Faster
With large keys, hard to break
Provides Confidentiality (but not authenticity and non-repudiation)

Asymmetric:
Key Management (Allows Public Key use)
- Distribution and Scaling
Can provide Authentication and Non-repudiation

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Diffie-Heliman Algorithm

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Asymmetric - The first agreement algorithm
Used to create a Symmetric key on both sides using local private and remove public

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RSA

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Defacto standard for digital signatures, key exchange, and encryption.

Uses large numbers factoring into their Prime Numbers.

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Trapdoor

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Information put in cyphertext using public key that is used by private key to decrypt

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El Gamal

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Asymmetric - slowest
Based on Diffie-Hellman
Used for digital signatures, encryption and key exchange

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ECC

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Asymmetric
Elliptic Curve Cryptosystems
Provides digital signatures, key exchange, and encryption.
ECC is more efficient using fewer resources
Ideal for wireless and cell phone devices

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Knapsack

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Asymmetric
Encryption only initially with digital signatures added later
Insecure and no longer used

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Zero Knowledge Proof

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Tell no more than is necessary.

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MAC

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Message Authentication Code
An authentication scheme which applies a secret key to a message.

3 basic types: Hash MAC (HMAC), CBC-MAC, CMAC

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HMAC

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Hash MAC
Integrity and Data Origin Authentication
No confidentiality

Symmetric key is added to message and hashed resulting in MAC appended to message.

Send to receiver, the message is used with receiver symmetric key and MACs should match. Confirms message was not altered and from which system it originated.

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CBC-MAC

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Integrity and Data Origin Authentication
No confidentiality

Does not do a one-way hash
Encrypts message with shared symmetric key and send plaintext and only the final block of the ciphertext.
Receiver uses key and plain text to match block of ciphertext.

Form of Authentication. Date Origin Authentication or System Authentication.

Weak because it is not bound to a user, only to devices.

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CMAC

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Version of CBC-MAC but more secure and approved to with with 3DES and AES.

Integrity and Data Origin Authentication
No confidentiality

Uses symmetric key to create subkeys to encrypt the individual blocks.

Outlined in 802.11i for block cipher AES

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Hash

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Integrity

Not confidentiality or authentication

Can detect only unintentional modifications

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Hash Value

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Message Digest or Fingerprint

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Hashing Algorthim

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Nonkeyed Message Digest

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MAC Synonym

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Message Integrity Code (MIC) or Modification Detection Code (MDC)

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MD2

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One way hash
128 bit message digest
Slowest MD

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MD4

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One way hash
128 bit message digest
high speed

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MD5

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Similar to MD4 but more complex

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HAVAL

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Variable length hash value. Mod of MD5 with more protection again attacks against MD5.

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SHA

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Secure Hash Algorithm
160 bit hash value
Used with DSA

Updated versions have different lengths

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Tiger

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192 bit hash

Not designed on MD4 thus no susceptible to MD4 style attacks

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Collision

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Same value for 2 distinctly different messages that are hashed

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Birthday Attack

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Start with the original message and the hash value

The replacement message is changed until the hash value matches the original, also know as a collision

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Digital Signature

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Integrity and Authentication and Nonrepudiation

Hash value encrypted with sender's private key

Hashing provides Integrity
Encrypting provides Authentication and Nonrepudation

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DSS

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Digital Signature Standard

US standard outlining approved algorithms for digital signatures for government authentication activities

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Key Clustering

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When using different keys on a plaintext message generates the same hash value.

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One-time Pad (OTP)

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If used correctly, impossible to crack

Key is same length as message

Uses modular addition bit by bit