RFC 2040 The RC5, RC5CBC

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RFC 2040The RC5, RC5-CBC RC5-CBC-Pad

Encryption Algorithm

GROUP
MEMBERS
Aayush Deep Garg
Ravi Kumar Gupta
Rajdeep Singh Chaudhary
Vikrant Arora
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INTRODUCTION

• The RC5 cipher takes a fixed size input and
  produces a fixed size output block using
  transformation that depend on a key.
• The RC5-CBC is the cipher block chaining mode for
  RC5. It can process messages whose length is a
  multiple of RC5 block cipher.
• The third, RC5-CBC-Pad , handles plaintext of any
  length.

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FEATURES

• Fast (Word Oriented)
• Adaptable to processors of different word length
• Variable length key
• Variable number of rounds.

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DESCRIPTION OF RC5

• ALGORITHM
• Key Expansion
• Encryption
• PRIMARY OPERATIONS
• Twos complement addition of words
• Bit-wise XOR of words o
• Cyclic rotation
  ltltlt

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KEY EXPANSION

• Key table has t 2(r 1) elements S0,1.t
• S is generated using b byte key
• Pwodd((e-2)2W)
• Qwodd((phi-1)2w)
• S0Pw
• Sisi-1Qw

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ENCRYPTION

• A A S0
• B B S1
• for i 1 to r
• A ( (A o B) ltltlt B) s2 i
• B ( (B o A) ltltlt A) s2 i 1

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DESCRIPTION OF RC5-CBC

• The RC5 Cipher Block Chaining is, as the name
  indicate, is the chaining mode of RC5.
• It takes input as a multiple of blocks and
  encrypts it by iteratively calling RC5.
• Thus RC5-CBC gives advantage of multiple blocks
  at a time.
• It can not handle plaintext.

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DESCRIPTION OF RC5-CBC-Pad

• The RC5-CBC-Pad handles plaintext of any length.
• If the plaintext is not a multiple of block size
  then all the possible blocks are encrypted
  iteratively.
• The final block, which is not of block size, is
  first padded with bits to convert it into a block
  size.
• The last block is then encrypted.

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SECURITY CONSIDERATIONS

• The length of the secret key helps determine the
  ciphers resistance to brute force key searching
  attacks.
• A key length of 128 bits should give adequate
  protection against brute force key searching by a
  well funded opponent for a couple decades.