C0 D0 K dividing K into two 28 bit parts C1 D1 r1C0 r1D0 shifting to the left

C0 d0 k dividing k into two 28 bit parts c1 d1 r1c0

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(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
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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
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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
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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.
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