I have the source code for RC5 encryption algorithm, but it is in C, well it is still cool since it is "portable" but I am actually looking for a PowerPC assembly code for the same, or at least for the Key Expansion, Encryption and Decryption routines.
The "formula" for RC5 is pretty interesting and looks like is made to be implemented in Assembler.
Not if it's x86 assembler. On the Pentium each rotate uses 4-5 non-pairable cycles, so rotates are very slow (each rotate is the equivalent of (in the best case) 8-10 normal instructions, so the two rotates in an RC5 round are the equivalent of 16-20 other instructions). According to Intel shifts and rotates have been optimised on the PPro so they're slight faster than on the P5, but I haven't looked at the details yet. I haven't tried to formulate the RC5 core in asm yet (because of the patent - what good is it writing code which noone can use?) but on Intel hardware it's certainly going to be a lot slower than it looks (the much more complex CAST core is faster than just the rotates from the RC5 core). This is kind of unfortunate, because it's a nice algorithm. Peter.