DATA ENCRYPTION STANDARD (DES)…
DATA ENCRYPTION STANDARD (DES)
DES - Data Encryption Standard என்பது ஒரு symmetric key block cipher. இதில்: Encryption மற்றும் Decryption இரண்டிற்கும் same secret key பயன்படுத்தப்படுகிறது. DES ஒரு plaintext block-ஐ fixed-size block ஆக எடுத்துக் கொண்டு பல rounds மூலம் ci…
Premium — locked
Advanced
22 min
118 cards
15 MCQs v3
This is a premium lesson. You can see the shape of every card — unlock to read them.
Unlock
Definition
DES - Data Encryption Standard என்பது ஒரு symmetric key block cipher. இதில்: Encryption மற்றும் Decrypti……
Simple Explanation
Suppose plaintext: HELLO... DES நேரடியாக letter-by-letter encrypt செய்யாது. Instead: Plaintext ↓ 64-bit……
Explanation
Full form
DES = Data Encryption Standard…
Algorithm
DES என்பது
Symmetric Cipher ↓ Block Ciph……
Important
Symmetric algorithm Block cip……
Explanation
History
DES IBM உருவாக்கிய Lucifer cipher-ஐ அடிப்படையாகக் கொண்டது. 1970s-ல் IBM மற்றும் U.S. Nat……
Comparison
DES-ன் முக்கிய properties
Important
Most important point
DES key: 64 bits என்று input ஆகும். ஆனால் actual encryption s……
Explanation
Parity bit
DES key-ல் ஒவ்வொரு 8-bit byte-க்கும் ஒரு parity bit இருக்கும். So: 8 b……
Explanation
Odd parity
Traditional DES key represent……
Definition
Meaning
ஒவ்வொரு 8-bit group-லுள்ள num……
Explanation
Example
1011001? First 7 bits-ல் 1s count e……
Flow
Des overall flow
64-bit Plaintext ↓ Initial Permuta……
16 Rounds ↓ L16 R16 ↓ Swap / ……
Explanation
Des complete structure
64-bit Plaintext | v Initial Permutation | v ------------------- | | L0 32-bit R0 32-bi……
Explanation
Initial permutation
DES processing ஆரம்பத்தில்: IP = Initial Perm……
Important
Initial Permutation encryption str……
Explanation
After initial permutation
64-bit input: 64 bits இரண்டு equal halves-ஆக divi……
Explanation
Des round
DES has: 16 rounds ஒவ்வொரு round-லும்: Li = R(i-……
Formula
Round formula
For round i: Li = R(i-1) Ri = L(i-1) ⊕ F(……
Simple Explanation
Simple round idea
Suppose: L0 = Left 32 bits R0 = Right 32 bits Round 1: L1 = R……
Explanation
F function
DES-ன் heart: F Function…
Flow: 32-bit R ↓ Expansion ↓ 48 bits ↓ XOR with 4……
Formula
F function formula
F(R,K) = P(S(E(R) XOR K)) Where: E = E……
Explanation
Step 1: expansion
Right half: 32 bits Expansion function ……
Explanation
Why 32 → 48?
Round key size: 48 bits So XOR செய்ய inpu……
Concept
Expansion concept
Expansion சில bits-ஐ repeat ச……
Concept
32 bits ↓ Certain boundary bi……
Explanation
Step 2: xor with round key
Expanded right half: 48 bits Round key: 48……
Table
XOR truth table
Explanation
Memory: Same → 0 Different → 1…
Explanation
Step 3: s-box
After XOR: 48 bits இந்த 48 bits: 8 groups ×……
Explanation
Number of s-boxes
DES has: 8 S-Boxes Named: S1 S2 S3 S4 S5 S6 S7 S8 Each S-B……
Explanation
S-box structure
Each DES S-box contains: 4 rows × 1……
Explanation
S-box row selection
6-bit input: b1 b2 b3 b4 b5 b6 Row is determined by: Fi……
Explanation
S-box column selection
Middle four bits: b2 b3 b4 b5 determ……
Real Life Example
S-box example
Suppose input: 011011 Bits: 0 1 1 0 1 1 Row bits: First + Last = 0 1 = binary 01 = Row 1 Column……
Important
Very important memory
For a 6-bit S-box input: 1 2 3 4 5 6 Row: 1st + 6t……
Explanation
Why s-box important?
DES-ல் S-box: Non-linear substitution provide செய்கிறது. இது DES security-க்க……
Explanation
Confusion
S-box முக்கியமாக: Confusion p……
Definition
Meaning
Key மற்றும் ciphertext இடையேய……
Explanation
Step 4: p-box permutation
8 S-box outputs: 8 × 4 = 32 bits combine செய்யப்படும். Then: P P……
Explanation
Diffusion
Permutation operations பல input bits-ன் influence-ஐ multiple output posit……
Explanation
Complete f function
R = 32 bits ↓ Expansion E ↓ 48 bits ↓ XOR ……
Flow
Round complete flow
Li-1 -------------------------> XOR ----> Ri ^ | Ri-1 ---> F(Ri-1,Ki) ……
Explanation
Key schedule
DES uses one effective: 56-bit key ஆனால் 16 rounds-க்கும் different round keys தேவை. Each round key: 48 bits ……
Explanation
Pc-1
Initial 64-bit key-ல் parity bits நீக்கப்பட்டு/permuted……
Output
Result
Explanation
Splitting key
56-bit key: 56 bits split: C0……
Explanation
Left circular shift
Each round-ல் C and D halves: Left Circular ……
Table
DES shift schedule
Explanation
Memory: Rounds 1, 2, 9, 16 → ……
Explanation
Circular shift
Suppose: 10110 One-bit left circular sh……
Explanation
Pc-2
After shifting: C_i + D_i = 5……
Output
Result
This is the round key: K1, K2……
Flow
Key generation flow
64-bit Key ↓ PC-1 ↓ 56 bits ↓ C0 28 bits + D0 28 bit……
Explanation
Round keys
DES produces: K1 K2 K3 ... K1……
Explanation
Final round
After 16 rounds: L16 R16 are produced. DES typical……
Explanation
Final permutation
Final permutation: FP is inverse of……
Explanation
Des encryption complete
64-bit Plaintext ↓ Initial Permutation ↓ L0 + R……
Explanation
Des decryption
DES decryption structure encr……
Comparison
Difference
Round keys reverse order-ல் பயன்படுத்தப்படும். Encryption……
Important
Important advantage of feistel
Feistel cipher-ல் encryption மற்றும் decryption alm……
Comparison
Des encryption vs decryption
Explanation
Des block size
DES block size: 64 bits This never……
Question
DES key length? Possible answers: 64 bits including parity……
Explanation
Why des became insecure
DES effective key size: 56 bits Possible keys: 2^56 Approximately……
Explanation
Brute force
Brute-force attacker: Try Key 1 Try Key 2 Try Key 3 ... Try all 2^56 k……
Explanation
Des challenger
Electronic Frontier Foundation-ன் DES Cracker project 1998-ல் DES-ன் 56-bit key s……
Explanation
Des replacement
DES replaced by stronger algo……
Explanation
Triple des
3DES / Triple DES என்பது DES operation-ஐ three times……
Flow
3des flow
Plaintext ↓ Encrypt K1 ↓ Decr……
Explanation
Why middle decrypt?
Historical backward compatibility with DES systems காரணமாக EDE structure பயன……
Explanation
Aes
DES-க்கு modern replacement: AES = Advanced Encryption St……
Comparison
Des vs aes
Comparison
Des vs 3des
Explanation
Confusion and diffusion
DES uses both: Confusion + Diffusion Confus……
Explanation
Avalanche effect
Good cipher property: One input bit change should cause many ciphertext bits to change. Plaintext 1 000……
Explanation
Why 16 rounds?
Single round enough security தராது. Repeated rounds: Substitution Permutation X……
Remember
8 S-Boxes Each: 6-bit input 4……
Explanation
Des number memory
இந்த sequence-ஐ நினைவில் வைத்……
Definition
Meaning
64-bit input key ↓ 56 effective bits ↓ 48-bit round key ……
Explanation
Super memory
DES DATA: 64-bit Block 64-bit Input Key 56-bit Effective Key……
Remember
R ↓ E ↓ XOR K ↓ S ↓ P Short: ……
Definition
Meaning
R = Right half E = Expansion ……
Common Mistake
Common error 1
Wrong: DES is asymmetric. Cor……
Common Mistake
Common error 2
Wrong: DES is stream cipher. ……
Common Mistake
Common error 3
Wrong: DES block size = 56 bits. Co……
Common Mistake
Common error 4
Wrong: DES uses 64 effective key bits. ……
Common Mistake
Common error 5
Wrong: DES has 8 rounds. Corr……
Common Mistake
Common error 6
Wrong: DES has 16 S-boxes. Co……
Common Mistake
Common error 7
Wrong: S-box converts 4 bits to……
Common Mistake
Common error 8
Wrong: Expansion converts 48 → 32. C……
Common Mistake
Common error 9
Wrong: DES decryption needs a different algorithm. Correct:……
Remember
DES = 64, 56, 16, 48, 8…
Definition
Meaning
64 = Block size 56 = Effectiv……
TRB Point
TRB / NET / SET exam-க்கு important: DES full form: Data Encryption Standard DES is a: Symmetric Block Cipher……
MCQ
DES stands for:…
MCQ
DES is a:…
MCQ
DES block size is:…
MCQ
DES effective key length is:…
MCQ
DES has how many rounds?…
MCQ
DES round key size is:…
MCQ
DES has how many S-boxes?…
MCQ
Each DES S-box converts:…
MCQ
DES expansion operation conve……
MCQ
S-box row is determined by:…
MCQ
DES uses which structure?…
MCQ
DES key has how many parity b……
MCQ
DES decryption uses round key……
MCQ
DES S-box mainly provides:…
MCQ
DES is considered insecure to……
TRB Point
Exam short answer
Data Encryption Standard (DES) என்பது 64-bit plaintext blocks-ஐ encrypt செய்யும் symmetric Feistel block ciph……
Summary
DES | ----------------------- | | Data Block Key 64 bits 64 bits | | | 8 parity | | | 56 bits | | | Key Sched……
Text size
Theme
Contents
Print / PDF