(C0, D0) = K', dividing K' into two 28-bit parts
(C1, D1) = (r1(C0), r1(D0)), shifting to the left
k1 = PC2(C1,D1), applying permuted choice 2 and returning 48
bits
(C2, D2) = (r2(C1), r2(D1)), shifting to the left

Network Security And Cryptology
19
For free study notes log on:
k2 = PC2(C2,D2), applying permuted choice 2 and returning 48
bits
......
k16 = PC2(C16,D16)
DES Key Schedule Supporting Tables :
Permuted Choice 1 - PC1 :
57
49
41
33
25
17
9
1
58
50
42
34
26
18
10
2
59
51
43
35
27
19
11
3
60
52
44
36
63
55
47
39
31
23
15
7
62
54
46
38
30
22
14
6
61
53
45
37
29
21
13
5
28
20
12
4
Permuted Choice 2 - PC2 :
14
17
11
24
1
5
3
28
15
6
21
10
23
19
12
4
26
8
16
7
27
20
13
2
41
52
31
37
47
55
30
40
51
45
33
48
44
49
39
56
34
53
46
42
50
36
29
32
Left shifts (number of bits to rotate) - r1, r2, ..., r16:
r1
r2
r3
r4
r5
r6
r7
r8
r9 r10 r11 r12 r13 r14 r15 r16
1
1
2
2
2
2
2
2
1
2
2
2
2
2
2
1

20
For free study notes log on:
Conclusions
:
DES is a 64-bit block cipher.
16 round keys are derived from a single 64-bit key.
Decryption algorithm is identical to the encryption algorithm
except for the order of the round keys.
(3)
DES-X :
In cryptography,
DES-X
(or
DESX
) is a variant on the DES
(Data Encryption Standard) block cipher intended to increase the
complexity of a brute force attack using a technique called
key
whitening
.
The algorithm was included in RSA Security's BSAFE cryptographic
library since the late 1980s.DES-X augments DES by XORing an extra
64 bits of key (K
1
) to the plaintext
before
applying DES, and then
XORing another 64 bits of key (K
2
)
after
the encryption :
The key size is thereby increased to 56 + 2 × 64 = 184 bits.
However, the effective key size (security) is only increased to 56+64-1-
lg(M) =119 - lg(M) = ~119 bits, where M is the number of known
plaintext/ciphertext pairs the adversary can obtain,and lg() denotes
the binary logarithm. (Because of this, some implementations actually
make K
2
a strong one way function of K
1
and K.)
DES-X also increases the strength of DES against
differential
cryptanalysis and linear cryptanalysis, although the improvement is
much smaller than in the case of brute force attacks. It is estimated that
differential cryptanalysis would require 2
61
chosen plaintexts (vs. 2
47
for DES), while linear cryptanalysis would require 2
60
known
plaintexts (vs. 2
43
for DES.) Note that with 2
64
plaintexts (known or
chosen being the same in this case), DES (or indeed any other block
cipher with a 64 bit block size) is totally broken via the elementary
codebook attack.
(4)
Advanced Encryption Standard
(
AES
) : In cryptography, the
Advanced Encryption Standard
(
AES
), also known as
Rijndael
, is a
block cipher adopted as an encryption standard by the U.S.
government. It has been analyzed extensively and is now used

Network Security And Cryptology
21
For free study notes log on:
worldwide, as was the case with its predecessor,
[3]
the Data Encryption
Standard (DES).
AES is one of the most popular algorithms used in symmetric key
cryptography. It is available by choice in many different encryption
packages. This marks the first time that the public has had access to a
cipher approved by NSA for top secret information.

#### You've reached the end of your free preview.

Want to read all 101 pages?

- Spring '16
- ruiz
- Cryptography, Log on, free study notes