RC5 has a variable-length secret cryptographic key specied by parameters b and K:
b The number of bytes in the secret key K. Allowable values of b are 0, 1,
..., 255.
K The b-byte secret key: K[0], K[1], ..., K[b 1]
RC5-
w=r=b. For example, RC5-32/16/10has 32-bit words, 16 rounds,
a 10-byte (80-bit) secret key variable, and an expanded key table of 2(16+1) = 34
words. The key-expansion algorithm initializes S from the user’s given secret key parameter K.
Denition of the Magic Constants The key-expansion algorithm uses two
word-sized binary constants P and Q .
They are dened for arbitrary w as
follows
= Odd((e 2)2 (1)
Q = Odd(( 1)2 (2)
where
e = 2:718281828459::: (base of natural logarithms)
= 1:618033988749::: (golden ratio)