Cryptography
Computer Science
Computer Catlog
Cryptography Catlog

Caesar Cipher
Digital Signature
Public key cryptography
Symmetric vs. public-key
Key Management
Stream Ciphers
Self-Synchronizing Ciphers
Feedback Shift Registers
Modes of Operation
Multiple Encryption
Transposition Ciphers
Substitution Ciphers
Poly-alpha Substitutions
Poly-alpha Cipher Machine
Cryptanalysis Ciphers
Data Encryption Standard
DES Algorithm
IDEA Algorithm
RC5 Algorithm
RSA Encryption
Rabin Encryption
ElGamal Encryption
MD4 & MD5
Secure Hash Algorithm
Kerberos Authentication
Diffie-Hellman protocols
Key Management Life Cycle

RC5


    The RC5 block cipher has a word-oriented architecture for variable word sizes w = 16, 32, or 64 bits. It has an extremely compact description, and is suitable for hardware or software. The number of rounds r and the key byte-length b are also variable. It is successively more completely identified as RC5-w, RC5-w/r, and RC5-w/r/b. RC5-32/12/16 is considered a common choice of parameters; r = 12 rounds are recommended for RC5-32, and r = 16 for RC5-64.


    Algorithm specifies RC5. Plaintext and ciphertext are blocks of bitlength 2w. Each of r rounds updates both w-bit data halves, using 2 subkeys in an input transformation and 2 more for each round. The only operations used, all on w-bit words, are addition mod
2w (), XOR (), and rotations (left and right ). The XOR operation is linear, while the addition may be considered nonlinear depending on the metric for linearity. The data dependent rotations featured in RC5 are the main nonlinear operation used: x y denotes cyclically shifting a w-bit word left y bits; the rotation-count y may be reduced mod w (the low-order lg(w) bits of y suffice). The key schedule expands a key of b bytes into 2r + 2 subkeys Ki of w bits each. Regarding packing/unpacking bytes into words, the byte-order is little-endian: for w = 32, the first plaintext byte goes in the low-order end of A, the fourth in A's high-order end, the fifth in B's low order end, and so on.

RC5 Algorithm

RC5 Key Schedule


    RC5 decryption: Decryption uses the Algorithm subkeys, operating on ciphertext
C = (A,B) as follows (subtraction is mod 2w, denoted ). For i from r down to 1 do:
B ((B K2i+1) A) A, A ((A K2i) B)B. Finally M (A K0;B K1).

RC5 Constants

    RC5-32/12/16 test vectors: For the hexadecimal plaintext M = 65C178B2 84D197CC and key K = 5269F149 D41BA015 2497574D 7F153125, RC5 with w = 32, r = 12, and b = 16 generates ciphertext C = EB44E415 DA319824.