OBJECTIVE 02 — SYMMETRIC ENCRYPTION ALGORITHMS

SYMMETRIC ENCRYPTION (RECAP – EXAM CONTEXT)

Property Description
Keys Same key for encryption and decryption
Speed Very fast
Usage Bulk data encryption
Weakness Key distribution

MEMORY HOOK:
Same key → speed

CLASSIFICATION OF SYMMETRIC ALGORITHMS

BY DATA HANDLING

Type Description
Block Cipher Encrypts fixed-size blocks
Stream Cipher Encrypts bit/byte stream

BLOCK CIPHERS (VERY HIGH EXAM WEIGHT)

DATA ENCRYPTION STANDARD (DES)

Property Value
Key size 56-bit
Block size 64-bit
Structure Feistel
Status Broken / insecure

LOGIC:

  • Uses substitution and permutation

  • Vulnerable to brute-force attacks

EXAM TRAP:
DES is NOT secure, even if implemented correctly.

MEMORY HOOK:
DES = Dead Encryption Standard

TRIPLE DES (3DES)

Property Value
Key size 112 or 168-bit
Block size 64-bit
Operation Encrypt–Decrypt–Encrypt
Status Deprecated but stronger than DES

LOGIC:

  • Applies DES three times

  • Slower than DES

EXAM TRAP:
3DES ≠ three different algorithms.

MEMORY HOOK:
DES × 3 = slow but safer

ADVANCED ENCRYPTION STANDARD (AES)

MOST IMPORTANT SYMMETRIC ALGORITHM IN CEH

Property Value
Key sizes 128, 192, 256-bit
Block size 128-bit
Structure Substitution–Permutation
Status Secure and recommended

LOGIC:

  • Faster than 3DES

  • Resistant to known attacks

EXAM TRAP:
AES is NOT Feistel-based.

MEMORY HOOK:
AES = gold standard

BLOWFISH

Property Value
Key size 32–448-bit
Block size 64-bit
Creator Bruce Schneier
Status Secure but aging

LOGIC:

  • Fast in software

  • Free and unpatented

MEMORY HOOK:
Blowfish = flexible key size

TWOFISH

Property Value
Key size Up to 256-bit
Block size 128-bit
Relation Successor to Blowfish
Status Secure

EXAM TRAP:
Twofish ≠ Blowfish upgrade inside AES (AES won Rijndael).

MEMORY HOOK:
Twofish = AES finalist

RC (RIVEST CIPHERS) FAMILY

RC2

Property Value
Key size Variable
Block size 64-bit
Status Weak

RC4 (STREAM CIPHER – IMPORTANT)

Property Value
Type Stream cipher
Key size 40–2048-bit
Usage SSL, WEP (historically)
Status Broken

EXAM TRAP:
RC4 vulnerabilities allow keystream reuse attacks.

MEMORY HOOK:
RC4 = Rapidly Cracked

RC5

Property Value
Block size Variable
Key size Variable
Rounds Variable
Status Experimental

RC6

Property Value
Block size 128-bit
Key size Up to 256-bit
Status AES finalist

MEMORY HOOK:
RC6 = AES runner-up

CAST (CARLISLE ADAMS AND STAFFORD TAVARES)

Property Value
Block size 64 or 128-bit
Key size Up to 256-bit
Usage PGP
Status Secure

GOST

Property Value
Origin Russia
Block size 64-bit
Key size 256-bit
Status Secure

MEMORY HOOK:
GOST = Russian crypto

CAMELLIA

Property Value
Block size 128-bit
Key sizes 128, 192, 256-bit
Status AES-equivalent

MEMORY HOOK:
Camellia = AES alternative

CHACHA20 (STREAM CIPHER – MODERN)

Property Value
Type Stream cipher
Key size 256-bit
Usage TLS, VPNs
Status Secure

LOGIC:

  • Faster than AES on mobile devices

  • Resistant to timing attacks

MEMORY HOOK:
ChaCha20 = modern RC4 replacement

BLOCK VS STREAM CIPHER (EXAM FAVORITE)

Feature Block Stream
Data handling Fixed blocks Continuous stream
Error impact Whole block Single bit
Examples AES, DES RC4, ChaCha20

MODES OF OPERATION (VERY HIGH YIELD)

Block ciphers require modes.

Mode Description
ECB Electronic Codebook (INSECURE)
CBC Cipher Block Chaining
CFB Cipher Feedback
OFB Output Feedback
CTR Counter
GCM Galois/Counter Mode

EXAM TRAP:
ECB reveals patterns.

MEMORY HOOK:
Never use ECB

OBJECTIVE 02 — MEMORY CHECKLIST

You must remember:

  • DES is broken

  • 3DES is slow

  • AES is standard

  • RC4 is insecure

  • ChaCha20 replaces RC4

  • Block vs Stream differences

  • ECB mode is insecure

  • AES block size is always 128-bit

STATUS

Objective 02: COMPLETE

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OBJECTIVE 03 — ASYMMETRIC ENCRYPTION ALGORITHMS (RSA, DSA, Diffie-Hellman, ECC, ElGamal)