1. Conventional Encryption: Algorithms
Some of the most important symmetric block ciphers in current use
Triple DES
IDEA
Blowfish
RC5
CAST-128
RC2

2. Multiple Encryption with DES
Triple DES
Multiple Encryption with DES
Double DES
C = EK2[EK1[P]]; D = DK1[DK2[C]]
112 bit key is safe from brute force attack
Need to examine if  K3 s.t. EK2[EK1[P]] = EK3[P]
The answer is No!! (Proved in 1992)
# of mappings between 64-bit blocks = 264! =
DES defines one mapping for each different key, for a total # of mappings: 256 <1017
If DES is used twice with different keys, it will produce one of the many mappings that is not defined by a single application of DES

3. Meet In The Middle Attack
Triple DES
Meet In The Middle Attack
Let X = EK1(P). Clearly X = DK2(C)
Given a known <P, C>, construct a table of size 256 with all values of K1 and EK1(P)
Sort on EK1(P)
Now decrypt C with all values of K2. Check all results against table
Any match is a candidate <K1, K2> pair
If this pair is checked with another plaintext-ciphertext pair, it can be determined with the probability (If this pair is correct with another plaintext-ciphertext pair, it is a correct key with the probability )
Total effort is O(256), not 2112 (Not much better than the 255 required for single DES)

4. Triple DES C = EK3(DK2(EK1(P)))
No cryptographic significance to middle decrypt operation
backwards compatible with existing single DES (K1 = K2 = K3)
Two-key Triple DES (K1 = K3) or three-key triple DES
Security of Triple DES
no known practical attacks
brute force search impossible
meet-in-the-middle attacks need 256 plaintext-ciphertext pairs per key
A popular current
alternative
Major disadvantage is
speed (3x slower)

5. International Data Encryption Algorithm (IDEA)
Xuejia Lai and James Massey, ETH (Swiss Federal Institute of Technology), 1991
Patented
patent is held by Ascom-Tech
Non-commercial use of IDEA is free. Commercial licenses can be obtained by contacting Ascom-Tech
Used in PGP
128-bit key, 64-bit block
Variant Feistel network (not Feistel)
Eight rounds + final transformation

6. IDEA
IDEA Basic Operations
Uses three operations. Each operation is performed on two 16-bit inputs to produce a single 16-bit output
Bit-by-bit XOR (  )
(Unsigned 16-bit integers) addition modulo ( )
(Unsigned 16-bit integers) multiplication modulo (except that a block of all zeros is treated as representing (  )
Three operations are incompatible in the sense that
No pair of the three operations satisfies a distributive law. e.g.,
a (b  c)  (a b)  (a c)
No pair of the three operations satisfies an associative law. e.g.,
a (b  c)  (a b)  c
In IDEA, confusion is achieved by using these three separate operations in combination
Provides a complex transformation of the input, making cryptanalysis much more difficult (than with a DES which uses just a single XOR)

7. IDEA Basic Operations - Examples
Examples for 2-bit operands

8. IDEA Basic Building Block, MA
Basic building block is the Multiplication/Addition (MA) structure
F1,F2: Two 16-bit values derived from
the plaintext
Z5,Z6: Two 16-bit subkeys derived from
the key
G1,G2: Two 16-bit outputs
In IDEA, diffusion is provided by MA
Each output bit depends on every bit of
inputs (plaintext-derived inputs and
subkey inputs)
This MA structure is repeated eight times,
providing very effective diffusion

9. Overall IDEA Encryption Structure

10. Single Round of IDEA (1st Round)
Transformation
Sub-encryption

11. Output Transformation Stage of IDEA

12. Subkey Generation 52 16-bit subkeys are generated from the 128-bit key
IDEA
Subkey Generation
52 16-bit subkeys are generated from the 128-bit key
The first eight subkeys, Z1, Z2, …, Z8, are taken directly from the key
Then a circular left shift of 25 bit positions is applied to the key, and the next eight keys are extracted.
This procedure is repeated until all 52 subkeys are generated

13. IDEA
IDEA Decryption
Use the same structure (algorithm) as the encryption, but with different subkeys
Decryption subkeys U1, …, U52 are derived from encryption subkeys

14. Encryption and Decryption Subkeys
IDEA
Encryption and Decryption Subkeys
Zj-1: multiplicative inverse; Zj  Zj-1 = 1
-Zj : additive inverse; -Zj Zj = 0

15. Blowfish Designed by Bruce Schneier, 1993
Freely available (Unpatented; Royalty-free; No license required; Free source code available)
Used in SSH, OpenBSD, IPSec
Block cipher: 64-bit block
Variable key length; 32 bits to 448 bits
Fast encryption (much faster than DES and IDEA)
Compact
Simple

16. Subkey and S-Box Generation
Blowfish
Subkey and S-Box Generation
The key ranging from 32 bits to 448 bits (1 to bit words) is stored in a K-array:
K1, K2, …, Kj  j  14
The bit subkeys are stored in the P-array: P1, P2, …, P18
There are 4 S-boxes, each with 8x32(=256) 32-bit entries
P-array and then 4 S-boxes are initialized with fractional part of :
S1,0, S1,1, …, S1,255
S2,0, S2,1, …, S2,255
S3,0, S3,1, …, S3,255
S4,0, S4,1, …, S4,255
P1= 243F6A8816
P2= 85A308D316
  
S4,254= 578FDFE316
S4,255= 3AC372E616

17. Subkey and S-Box Initialization
Blowfish
Subkey and S-Box Initialization
P-array is XORed with K-array (reusing K-array if necessary): P1 = P1  K1, P2 = P2  K2, …, Pj = Pj  Kj, Pj+1 = Pj+1  K1, Pj+2 = Pj+2  K2, …
Then update P-array and S-boxes as follows:
Where EP,S[Y] is the ciphertext produced by encrypting Y using Blowfish with the P and S arrays
521 executions in total are required to produce the final P and S arrays
P1, P2 = EP,S[0]
P3, P4 = EP,S[P1 || P2]
  
P17, P18 = EP,S[P15 || P16]
S1,0, S1,1 = EP,S[P17 || P18]
S4,254, S4,255 = EP,S[P4,252 || P4,253]

18. Blowfish Encryption/Decryption
Slight variant of classic Feistel network
L and R are both processed in each round
16 rounds
Two extra XORs at the end 

19. Single Blowfish Round Uses addition modulo 232 and XOR
Round function processes four bytes
F(a, b, c, d) = ((S1,a + S2,b)  S3,c) + S4,d
Followed by Feistel swap 

20. Characteristics of Blowfish
Key-dependent S-Boxes
Operations are performed on both halves of data
Time-consuming subkey generation process
Makes it bad for rapid key switching, but makes brute force expensive
Perfect avalanche effect
Fast

21. RC5
RC5
Designed by Ronald Rivest (MIT Prof.) for RSA Data Security
Secret-key block cipher
Parameterized algorithm
Features
Data-dependent rotations
Variable block size
Variable key size
Variable number of rounds

22. Motivations Suitable for hardware and software Fast
RC5
Motivations
Suitable for hardware and software
Fast
Adaptable to processors of different word lengths
Variable number of rounds
Variable-length key
Simple
Low memory usage
High security
Emphasis of data-dependent rotations

23. Parameterization RC5 is word-oriented Representation
Two-word input and two-word output
Representation
Word size: w (16,32,64)
Number of rounds: r (0,1, …, 255)
Number of bytes in key K: b (0,1, …, 255)
RC5 algorithm notation: RC5-w/r/b
RC5 algorithm example: RC5-32/16/7
Similar to DES
Two 32-bit word inputs and outputs
16 rounds
7-byte (56-bit) key
RC5-32/12/16
“nominal” version

24. RC5
Key Expansion
RC5 performs complex operations on the secret key to generate a total of t subkeys, which are stored in S array, S[0],S[1], …, S[t-1]
Each subkey is one word (w bits) in length
Two subkeys are used in each round, and two more subkeys are used outside the r-round  t = 2r+2
In key expansion, magic constants are used
Pw = Odd((e - 2)2w); e= …. (base of natural logarithms)
Qw = Odd(( - 1)2w); = …. (golden ratio = (1+sqr(5))/2)
Odd(x): odd integer nearest to x
Example w
Pw B7E1 B7E B7E151628AED2A6B
Qw 9E37 9E3779B9 9E3779B97F4A7C15

25. Key Expansion Algorithm
RC5
Key Expansion Algorithm
Step-1: Convert secret key bytes to words
b byte key K, (K[0], K[1], …, K[b-1]) is converted to word array L[0], L[1], …, L[c-1]
Step-2: Initialize subkey array S (S[0], S[1], …, S[t-1])
S[0] = Pw;
for i=1 to t-1 do
s[i] = s[i-1] + Qw;
Step-3: Mix the secret key into subkey array S
i=j=X=Y=0;
Do 3*max(t, c) times:
X=S[i]=(S[i]+X+Y)<<<3;
Y=L[j]=(L[j]+X+Y)<<<(X+Y);
i=(i+1) mod t;
j=(j+1) mod c;
Note: <<<  cyclic rotate left

26. RC5
RC5 Key Expansion

27. RC5 Encryption RC5 uses 3 primitive operations Encryption
Addition, Subtraction (of words): modulo 2w
Bitwise XOR
Left, right circular rotation
Encryption 
LE0 = A + S[0];
RE0 = B + S[1];
for i = 1 to r do
LEi = ((LEi-1  REi-1) <<< REi-1) + S[2i];
REi = ((REi-1  LEi) <<< LEi) + S[2i+1];

28. RC5 Decryption for i = r downto 1 do
for i = r downto 1 do
RDi-1 = ((RDi – S[2i+1] >>> LDi)  LDi) ;
LDi-1 = ((LDi – S[2i] >>> Rdi-1)  RDi-1) ;
B = RD0 - S[1];
A = LD0 - S[0];

29. CAST-128 Developed by Carlisle Adams and Stafford Tavares
Used in IPSec
64-bit block, 40- to 128-bit keys (in 8-bit increments)
Classical Feistel network structure
Sixteen rounds
Two subkeys per round, one 32-bit (Kmi), one 5-bit (Kri)
Three different round functions
Four operations: addition(+) and subtraction(-) modulo 232, XOR, and (variable) circular left rotate (<<<)
5-bit subkey (Kri) determines rotate amount
Encryption
Decryption: same as encryption with the keys applied in reverse order
L0||R0 = Plaintext
for i = 1 to 16 do
Li = Ri-1
Ri = Li-1  Fi[Ri-1, Kmi, Kri];
Ciphertext = L16||R16

30. CAST-128 Round Function F Definition of F  I Ia Ib Ic Id
Rounds 1,4 I=(Kmi+ Ri-1)<<<Kri)
7,10,13,16 F=((S1[Ia]S2[Ib])-S3[Ic])+S4[Id]
Rounds 2,5 I=(KmiRi-1)<<<Kri)
8,11, F=((S1[Ia]-S2[Ib])+S3[Ic])S4[Id]
Rounds 3,6 I=(Kmi-Ri-1)<<<Kri)
9,12, F=((S1[Ia]+S2[Ib])S3[Ic])-S4[Id]

31. CAST-128 S-Boxes CAST-128 uses 8 S-boxes
Four of these, S-box 1 thru S-box 4 are used in the encryption/decryption process
S-box 5 thru S-box 8 are used in the subkey generation
S-boxes contain fixed (predefined) values
Each S-box contains bit values

32. CAST-128 Subkey Generation
Label the 128-bit (16-byte) key as:
x0x1x3x4x5x6x7x8xAxBxCxDxExF
Symbol Definitions
Km1, …, Km16 Sixteen 32-bit masking subkeys (one per round)
Kr1, …, Kr16 Sixteen 32-bit rotate subkeys (one per round), of which
only the least significant 5 bits of each are used
z0, …, zF Intermediate (temporary) bytes
K1, …, K32 Intermediate (temporary) words
K1 thru K32 are calculated from the key using S-boxes 5 thru 8 (See next pages)
Then subkeys are defined as
for i = 1 to 16 do
Kmi = Ki;
Kri = K16+i;

33. CAST-128 Subkey Generation
z0z1z2z3 = x0x1x2x3  S5[xD]  S6[xF]  S7[xC]  S8[xE]  S7[x8]
z4z5z6z7 = x8x9xAxB  S5[z0]  S6[z2]  S7[z1]  S8[z3]  S8[xA]
z8z9zAzB = xCxDxExF  S5[z7]  S6[z6]  S7[z5]  S8[z4]  S5[x9]
zCzDzEzF = x4x5x6x7  S5[zA]  S6[z9]  S7[zB]  S8[z8]  S6[xB]
K1 = S5[z8]  S6[z9]  S7[z7]  S8[z6]  S5[z2]
K2 = S5[zA]  S6[zB]  S7[z5]  S8[z4]  S6[z6]
K3 = S5[zC]  S6[zD]  S7[z3]  S8[z2]  S7[z9]
K4 = S5[zE]  S6[zF]  S7[z1]  S8[z0]  S8[zC]
x0x1x2x3 = z8z9zAzB  S5[z5]  S6[z7]  S7[z4]  S8[z6]  S7[z0]
x4x5x6x7 = z0z1z2z3  S5[x0]  S6[x2]  S7[x1]  S8[x3]  S8[z2]
x8x9xAxB = z4z5z6z7  S5[x7]  S6[x6]  S7[x5]  S8[x4]  S5[z1]
xCxDxExF = zCzDzEzF  S5[xA]  S6[x9]  S7[xB]  S8[x8]  S6[z3]
K5 = S5[x3]  S6[x2]  S7[xC]  S8[xD]  S5[x8]
K6 = S5[x1]  S6[x0]  S7[xE]  S8[xF]  S6[xD]
K7 = S5[x7]  S6[x6]  S7[x8]  S8[x9]  S7[x3]
K8 = S5[x5]  S6[x4]  S7[xA]  S8[xB]  S8[x7]
K9 = S5[z3]  S6[z2]  S7[zC]  S8[zD]  S5[z9]
K10 = S5[z1]  S6[z0]  S7[zE]  S8[zF]  S6[zC]
K11 = S5[z7]  S6[z6]  S7[z8]  S8[z9]  S7[z2]
K12 = S5[z5]  S6[z4]  S7[zA]  S8[zB]  S8[z6]
K13 = S5[x8]  S6[x9]  S7[x7]  S8[x6]  S5[x3]
K14 = S5[xA]  S6[xB]  S7[x5]  S8[x4]  S6[x7]
K15 = S5[xC]  S6[xD]  S7[x3]  S8[x2]  S7[x8]
K16 = S5[xE]  S6[xF]  S7[x1]  S8[x0]  S8[xD]

34. CAST-128 Subkey Generation
z0z1z2z3 = x0x1x2x3  S5[xD]  S6[xF]  S7[xC]  S8[xE]  S7[x8]
z4z5z6z7 = x8x9xAxB  S5[z0]  S6[z2]  S7[z1]  S8[z3]  S8[xA]
z8z9zAzB = xCxDxExF  S5[z7]  S6[z6]  S7[z5]  S8[z4]  S5[x9]
zCzDzEzF = x4x5x6x7  S5[zA]  S6[z9]  S7[zB]  S8[z8]  S6[xB]
K17 = S5[z8]  S6[z9]  S7[z7]  S8[z6]  S5[z2]
K18 = S5[zA]  S6[zB]  S7[z5]  S8[z4]  S6[z6]
K19 = S5[zC]  S6[zD]  S7[z3]  S8[z2]  S7[z9]
K20 = S5[zE]  S6[zF]  S7[z1]  S8[z0]  S8[zC]
x0x1x2x3 = z8z9zAzB  S5[z5]  S6[z7]  S7[z4]  S8[z6]  S7[z0]
x4x5x6x7 = z0z1z2z3  S5[x0]  S6[x2]  S7[x1]  S8[x3]  S8[z2]
x8x9xAxB = z4z5z6z7  S5[x7]  S6[x6]  S7[x5]  S8[x4]  S5[z1]
xCxDxExF = zCzDzEzF  S5[xA]  S6[x9]  S7[xB]  S8[x8]  S6[z3]
K21 = S5[x3]  S6[x2]  S7[xC]  S8[xD]  S5[x8]
K22 = S5[x1]  S6[x0]  S7[xE]  S8[xF]  S6[xD]
K23 = S5[x7]  S6[x6]  S7[x8]  S8[x9]  S7[x3]
K24 = S5[x5]  S6[x4]  S7[xA]  S8[xB]  S8[x7]
K25 = S5[z3]  S6[z2]  S7[zC]  S8[zD]  S5[z9]
K26 = S5[z1]  S6[z0]  S7[zE]  S8[zF]  S6[zC]
K27 = S5[z7]  S6[z6]  S7[z8]  S8[z9]  S7[z2]
K28 = S5[z5]  S6[z4]  S7[zA]  S8[zB]  S8[z6]
K29 = S5[x8]  S6[x9]  S7[x7]  S8[x6]  S5[x3]
K30 = S5[xA]  S6[xB]  S7[x5]  S8[x4]  S6[x7]
K31 = S5[xC]  S6[xD]  S7[x3]  S8[x2]  S7[x8]
K32 = S5[xE]  S6[xF]  S7[x1]  S8[x0]  S8[xD]

35. CAST-128 S-Box S1 CAST-128 S-Box S1
30fb40d4 9fa0ff0b 6beccd2f 3f258c7a 1e213f2f 9c004dd3 6003e540 cf9fc949 bfd4af27 88bbbdb5 e d e63a0e0 15c361d2 c2e7661d 22d4ff8e 28683b6f c07fd059 ff2379c8 775f50e2 43c340d3 df2f ca41a a2d2bd2d a1c9e0d6 346c b76d f2f 2abe32e1 aa54166b 22568e3a a2d341d0 66db40c8 a784392f 004dff2f 2db9d2de 97943fac 4a97c1d b7 b5f437a7 b82cbaef d751d159 6ff7f0ed 5a097a1f 827b68d0 90ecf52e 22b0c054 bc8e5935 4b6d2f7f 50bb64a2 d bee5812d b e93b159f b48ee411 4bff345d fd45c240 ad31973f c4f6d02e 55fc8165 d5b1caad a1ac2dae a2d4b76d c19b0c f2 0c6e4f38 a4e4bfd7 4f5ba c1d2f c59c5319 b949e354 b04669fe b1b6ab8a c71358dd 6385c f935d 57538ad5 6a e63d37e0 2a54f6b3 3a787d5f 6276a0b5 19a6fcdf 7a42206a 29f9d4d5 f61b1891 bb72275e aa c6b505eb 84c7cb8c 2ad75a0f 874a1427 a2d1936b 2ad286af aa56d291 d c750d 93b39e c9 6c00b32d 73e2bb14 a0bebc3c eab 3f328b cf82 59a2cea6 04ee002e 89fe78e6 3fab ff6c f c5c8 76cb5ad6 d49974c9 ca180dcf d5 c7fa5cf6 8ac e79e13 47da91d0 f40f9086 a7e2419e ef495 aa573b04 4a805d8d d a3c bf64cddf ba57a68e 75c6372b 50afd341 a7c a0bf5 6b54bfab 2b0b1426 ab4cc9d7 449ccd82 f7fbf265 ab85c5f3 1b55db94 aad4e324 cfa4bd3f 2deaa3e2 9e204d02 c8bd25ac eadf55b3 d5bd9e98 e31231b2 2ad5ad6c de adbe4528 d8710f69 aa51c90f aa786bf f1e aa51a79b 2ad344cc 7b5a41f0 d37cfbad 1b ece491 b4c332e d4 c9600acc ce387e6d bf6bb16c 6a70fb78 0d03d9c9 d4df39de e01063da 4736f464 5ad328d8 b347cc96 75bb0fc bfb 4ffbcc35 b58bcf6a e11f0abc bfc5fe4a a70aec10 ac39570a 3f04442f 6188b153 e0397a2e 5727cb79 9ceb418f 1cacd68d 2ad37c cb9d c69dff09 c75b65f0 d9db40d8 ec0e ead4 b11c3274 dd24cb9e 7e1c54bd f01144f9 d2240eb1 9675b3fd a3ac3755 d47c27af 51c85f4d a5bb15e f0 ca042cf1 011a37ea 8dbfaadb 35ba3e4a 3526ffa0 c37b4d09 bc306ed9 98a f725 ff5e569d 0ced63d0 7c63b2cf 700b45e1 d5ea50f1 85a92872 af1fbda7 d a7870bf3 2d3b4d79 42e cd0ede db8 f881814c 474d6ad7 7c0c5e5c d b7298 f5d2f4db ab e2f1e c9e bd91e046 9a56456e dc39200c 20c8c bda1c e1e696ff b141ab08 7cca89b9 1a69e783 02cc4843 a2f7c ef47d 427b169c 5ac9f049 dd8f0f00 5c8165bf

36. RC2 Developed by Ron Rivest (RSA Data Security) 64-bit block cipher
Variable key size (from one byte up to 128 bytes)
Designed to be easy to implement on 16-bit microprocessor
Use 16-bit word, 16-bit arithmetic (addition, XOR, AND, ~, rotate)
Non-Feistel
18 rounds (mixing/mashing)
Used in S/MIME

37. RC2 Key Expansion RC2 assumes 128 (64 word) byte key buffer
For byte operation, key array is L[0], …, L[127]; each L[i] is a byte
For word operation, key array is K[0], …, K[63]; each K[i] is a 16-bit word
These are alternative views of the same key buffer
Key expansion
Assume that exactly T bytes of key are supplied, 1  T  128
The purpose of key expansion algorithm is to modify the key buffer so that each bit of the expanded key depends in a complicated way on every bit of the supplied input key
Key expansion begins by placing the supplied T-byte key into bytes L[0], …, L[T-1] of the key buffer
L array is then computed making use of an auxiliary array P
P array is a random permutation of values of 0,…,255, which is constructed based on p= … (See next page)
The computation is
for i = T to 127 do
L[i] = P[L[i-1] + L[i-T]];
L[128-T] = P[L[128-T]]
For i = 127 – T down to 0 do
L[i]=P[L[i+1]  L[i+T]];

38. PiTable (P-array) Here is the P array in hexadecimal notation:
RC2
PiTable (P-array)
Here is the P array in hexadecimal notation:
a b c d e f
00: d9 78 f9 c4 19 dd b5 ed 28 e9 fd 79 4a a0 d8 9d
10: c6 7e b e 62 4c b fb a2
20: 17 9a 59 f5 87 b3 4f d 8d d 32
30: bd 8f 40 eb 86 b7 7b 0b f c 6b 4e 82
40: 54 d ce 60 b2 1c c0 14 a7 8c f1 dc
50: ca 1f 3b be e4 d1 42 3d d4 30 a3 3c b6 26
60: 6f bf 0e da f2 1d 9b bc
70: f8 11 c7 f6 90 ef 3e e7 06 c3 d5 2f c8 66 1e d7
80: 08 e8 ea de ee f7 84 aa 72 ac 35 4d 6a 2a
90: 96 1a d2 71 5a b 9f d0 5e a4 ec
a0: c2 e0 41 6e 0f 51 cb cc af 50 a1 f
b0: 99 7c 3a b8 b4 7a fc b
c0: 2d 5d fa 98 e3 8a 92 ae 05 df c ba c9
d0: d3 00 e6 cf e1 9e a8 2c f 58 e2 89 a9
e0: 0d b ab 33 ff b0 bb 48 0c 5f b9 b1 cd 2e
f0: c5 f3 db 47 e5 a5 9c 77 0a a fe 7f c1 ad

39. RC2
RC2 Encryption
Encryption algorithm takes a 64-bit input stored in R[0], R[1], R[2], R[3], and places the result back in R[0] thru R[3].
Algorithm consists of 18 rounds of two types: mixing and mashing
Mixing round:
R[0] = R[0] + K[j] + (R[3] & R[2]) + ((~R[3] & R[1]);
R[0] = R[0] <<< 1;
j = j + 1;
R[1] = R[1] + K[j] + (R[0] & R[3]) + ((~R[0] & R[2]);
R[1] = R[1] <<< 2;
R[2] = R[2] + K[j] + (R[1] & R[0]) + ((~R[1] & R[3]);
R[2] = R[2] <<< 3;
R[3] = R[3] + K[j] + (R[2] & R[1]) + ((~R[2] & R[0]);
R[3] = R[3] <<< 5;
Here j is the global variable; K[j] is the first
subkey word that has not yet been used

40. RC2 Encryption Mashing round RC2
Initialize j to zero
Perform five mixing rounds (j = 20)
Perform one mashing round
Perform six mixing rounds (j = 44)
Perform five mixing rounds (j=64)
Decryption: Inverse operation of encryption with the keys used in reverse order
R[0] = R[0] + K[R[3] & 63];
R[1] = R[1] + K[R[0] & 63];
R[2] = R[2] + K[R[1] & 63];
R[3] = R[3] + K[R[2] & 63];

41. Characteristics of Advanced Block Ciphers
Key features found in advanced symmetric block ciphers (not in DES)
Variable key length
Blowfish, RC5, CAST-128, RC2
Mixed operators
More than one arithmetic and/or Boolean operator, especially ones that are not associative or distributive
These operators provide nonlinearity as an alternative to S-boxes
Data-dependent rotation
Provide excellent confusion and diffusion
RC5
Key-dependent rotation
CAST-128

42. Characteristics of Advanced Block Ciphers
Key-dependent S-boxes
Blowfish
Expensive key schedule computation
Variable round function (F)
CAST-128
Variable plaintext/ciphertext block length
RC5
Variable number of rounds
Operation on both data halves each round
IDEA, Blowfish, RC5

43. Chapter 4 HW
Prob. 4.5
Prob. 4.8
Prob. 4.9
Prob. 4.13