CYG Chapter 5 Fast Block Ciphers

Questions about the lecture 'Cryptography' of the RWTH Aachen Chapter 5 Fast Block Ciphers

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This flashcard set delves into advanced university-level concepts of fast block ciphers, focusing on encryption modes like ECB, CNC, OFB, CFB, and CTR. It covers the characteristics and steps of AES, including key generation, encryption processes, and security aspects. The set also explores DES, its vulnerabilities, and modern alternatives like IDEA, Blowfish, and Twofish. Ideal for computer science students and professionals, this flashcard set provides a comprehensive overview of fast block cipher mechanisms, their applications, and security considerations.

Cartes-fiches

Utilisateurs

Langue

Anglais

Catégorie

Informatique

Niveau

Université

Créé / Mis à jour

21.03.2017 / 20.08.2017

Fichiers de cartes similaires

What is the definition?

[4tpoly.mixcolumns.encryption.AES.fastblockciphers, 3+2]

1. f=c₃u³+…+c₀

2. Multiply by fix polynomial a(u)=(x+1)u³+u²+u+x

3. Reduce modulo u⁴+1 afterwards

4. Can be rewritten as T*c

5. T has rows starting with (x, x+1, 1, 1)

What is the definition?

[addroundkey.encryption.AES.fastblockciphers]

Perform bitwise xor with roundkey K_i in i^thround

What is the definition?

[decryption.AES.fastblockciphers]

Use encryption algorithm with inverted transformations in reverse

What are the characteristics?

[security.AES.fastblockciphers, 2]

1. Design criteria of AES are fully documented and discussed

2. Open discussion foreclosed suspicion of built-in trapdoors

List them!

[designcriteria.security.AES.fastblockciphers, 6]

1. If 1 byte is modified then 16 bytes are modified after 2 rounds

2. S-Boxes are non-linear to resist differential cryptanalysis

3. Simple algebraic design allows efficient implementations

4. ShiftRows avoids ‘truncated differential-’ and ‘square attack’

5. MixColumns causes diffusion among bytes

6. KeySchedula avoids advantages from knowing parts of the key

What are the characteristics?

[attacks.security.AES.fastblockciphers, 3]

1. AES128, AES192 and AES256 are attacked by exhaustive key search

2. Faster attacks can be applied when reducing number of rounds

3. Attacks with complexity 2¹¹⁹ and 2^99.5 are known since 2009

What happened 9.1997?

[history.fastblockciphers]

NIST solicited 21 proposals for a replacement for DES till 6.1998

What are the requirements?

[9.1997.history.fastblockciphers, 2]

1. Block length of 128 bits

2. Key length of 128, 192 and 256 bits

Who are the competitors?

[9.1997.history.fastblockciphers, 5]

1. Rijn-dael by Rijmen and Daemen won

2. MARS by IBM

3. RCG by RSA

4. Serpent by Biham

5. Twofish by Schneier et al.

List them!

[others.fastblockciphers, 6]

1. IDEA by Lai and Massey

2. Blowfish

3. Khazad

4. Anubis

5. Serpent

6. Twofish

What are the characteristics?

[IDEA.others.fastblockciphers, 3]

1. First presented on Eurocrypt in 1990

2. Patented in Europe and USA

3. Non-commercial use is free

How do we define the blockcipher?

[modes.fastblockciphers]

Blockcipher with key K is defined as E_K

List them!

[modes.fastblockciphers, 5]

1. ECB

2. CNC

3. OFB

4. CFB

5. CTR

What is the definition?

[ECB.modes.fastblockciphers, 2]

1. C_i= E_K(M_i)

2. M_i= E_K^-1(C_i)

What is the definition?

[CNC.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector C₀

2. C_i= E_K(M_i xor C_i-1)

3. M_i= E_K^-1(C_i) xor C_i-1

What is the definition?

[OFB.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector Z₀= C₀and keystream Z_i=E_K(Z_i-1)

2. C_i= M_ixor Z_i

3. M_i= C_ixor Z_i

What is the definition?

[CFB.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector Z₀= C₀and keystream Z_i=E_K(C_i-1)

2. C_i= M_ixor Z_i

3. M_i= C_ixor Z_i= C_ixor E_K(C_i-1)

What is the definition?

[CTR.modes.fastblockciphers, 1+2]

1. Use non-secret initial counter Z₁= C₀

2. C_i= E_K(Z_i) xor M_i

3. M_i= E_K(Z_i)xor C_i

What is the definition?

[messageauth.modes.fastblockciphers, 3]

1. Modifying one pt must affect all subsequent blocks // CBC and CFB

2. Compute C_n for M=(M₁,…,M_n)

3. If M is tampered by Oscar into M’ then C_n does not fit M’

What is the definition?

[sharingpassword.modes.fastblockciphers, 2]

1. Generate key K = k(name, password)

2. Store tuple (name, E_K(password))

What happened 15.5.1973?

[history.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

NBS solicited proposals for a cs, choosing DES based on LUCIFER by IBM (Adler et al.)

What happened 1975?

[history.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Rumors say that IBM or the NSA installed trapdoor in DES

What happened 17.3.1975?

[history.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

DES being published and starting a public discussion

What happened 1.1977?

[history.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

DES adopted as a standard for unclassified applications

What happened 1999?

[history.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Last review of DES in a 5 years loop // Was dedicated for 10-15 years and proved to be more durable

What is the definition?

[keygeneration.DES.fastblockciphers]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

K₀=(k₁, …,k₇,b₁,k₉, …,k₆₃,b₈) // 56 bits, extended by 8 (odd) parity bits for each 7 bits for error detection

What are the steps?

[roundkeys.keygeneration.DES.fastblockciphers, 3]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

1. Devide 56 key bits into 28 bits each C₀ and D₀

2. Generate C_n,D_n via cyclic leftshift by s_n from C_n-1,D_n-1with n = 1,…,16 and s_n := {If n \in {1,2,9,16} then 1; else 2}

3. Of each (C_n,D_n) select 48 bit

What are the steps?

[encryption.DES.fastblockciphers, 4]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

1. Get IPof input bits and divide plaintext into blocks of 64 bits

2. Split into two blocks of 32 bits

3. 16 rounds of SBB

4. Obtain inverse IP^-¹

What are the steps?

[SBB.encryption.DES.fastblockciphers, 3]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

1. Expansion map E doubles 16 of 32 input bits and permutes resulting 48 bits

2. Proceed bitwise xor with round key K_i

3. Obtain P via transformation S

What is the definition?

[S.SBB.encryption.DES.fastblockciphers, 4]

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

1. {0,1}⁴⁸→ {0,1}³²

2. Divide 48 bits into 8 blocks of 6 bits

3. r = 2*b_i1 + b_i6

4. s = Sum_j=2⁵2^5-j*b_ij

What holds?

[encryption.DES.fastblockciphers, 2]

1. L_i = R_i-1, R_i = L_i-1 xor f(R_i-1,K_i)

2. R_i-1= L_i, L_i-1 = R_i xor f(L_i,K_i)

What is the definition?

[decryption.DES.fastblockciphers]

Use encryption algorithm with keys in reverse

What are the characteristics?

[exhaustive.security.DES.fastblockciphers, 2]

1. Look for 2⁵⁶ possible keys

2. Realized in 1999 with 100.000 workstations in 22h

What are the characteristics?

[differential.security.DES.fastblockciphers, 3]

1. Lower complexity of attack with differential cryptanalysis

2. Realized in 1992 at CRYPTO by Biham and Shamir

3. Attack is still complex due to S-Boxes // Did IBM knew about this?

What holds for nowadays?

[security.DES.fastblockciphers]

DES can be broken with todays hardware in relatively short time

What is the definition?

[triple.DES.fastblockciphers, 3]

1. Perform DES three times with different keys

2. c = DES_K3(DES_K2^-1(DES_K1(m))) or DES_K1(DES_K2^-1(DES_K1(m)))

3. Ensure compatibility with DES via second step and K₁=K₂=K₃

What are the options?

[keygeneration.AES.fastblockciphers, 3]

K₀ has a length of 128, 192 or 256 bits

What defines the number?

[roundkey.keygeneration.AES.fastblockciphers]

r := {10 for 128 bits; 12 for 192 bits; 14 for 256 bits}

How are they organized?

[roundkey.keygeneration.AES.fastblockciphers]

Organize each roundkey into a 4x4 matrix of bytes

What is the definition?

[keyexpansion.roundkey.keygeneration.AES.fastblockciphers]

Generates r+1 round keys of 128 bits // Similar for other sizes

1 / 53

Cartes-fiches

What are the requirements?

[9.1997.history.fastblockciphers, 2]

1. Block length of 128 bits

2. Key length of 128, 192 and 256 bits

Who are the competitors?

[9.1997.history.fastblockciphers, 5]

1. Rijn-dael by Rijmen and Daemen won

2. MARS by IBM

3. RCG by RSA

4. Serpent by Biham

5. Twofish by Schneier et al.

List them!

[others.fastblockciphers, 6]

1. IDEA by Lai and Massey

2. Blowfish

3. Khazad

4. Anubis

5. Serpent

6. Twofish

What are the characteristics?

[IDEA.others.fastblockciphers, 3]

1. First presented on Eurocrypt in 1990

2. Patented in Europe and USA

3. Non-commercial use is free

How do we define the blockcipher?

[modes.fastblockciphers]

Blockcipher with key K is defined as E_K

List them!

[modes.fastblockciphers, 5]

1. ECB

2. CNC

3. OFB

4. CFB

5. CTR

What is the definition?

[ECB.modes.fastblockciphers, 2]

1. C_i= E_K(M_i)

2. M_i= E_K^-1(C_i)

What is the definition?

[CNC.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector C₀

2. C_i= E_K(M_i xor C_i-1)

3. M_i= E_K^-1(C_i) xor C_i-1

What is the definition?

[OFB.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector Z₀= C₀and keystream Z_i=E_K(Z_i-1)

2. C_i= M_ixor Z_i

3. M_i= C_ixor Z_i

What is the definition?

[CFB.modes.fastblockciphers, 1+2]

1. Use non-secret initial vector Z₀= C₀and keystream Z_i=E_K(C_i-1)

2. C_i= M_ixor Z_i

3. M_i= C_ixor Z_i= C_ixor E_K(C_i-1)

What is the definition?

[CTR.modes.fastblockciphers, 1+2]

1. Use non-secret initial counter Z₁= C₀

2. C_i= E_K(Z_i) xor M_i

3. M_i= E_K(Z_i)xor C_i

What is the definition?

[messageauth.modes.fastblockciphers, 3]

1. Modifying one pt must affect all subsequent blocks // CBC and CFB

2. Compute C_n for M=(M₁,…,M_n)

3. If M is tampered by Oscar into M’ then C_n does not fit M’

What is the definition?

[sharingpassword.modes.fastblockciphers, 2]

1. Generate key K = k(name, password)

2. Store tuple (name, E_K(password))

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CYG Chapter 5 Fast Block Ciphers

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