RC5 is a fast block cipher developed based on RC4. Set elements are reordered in RC5 algorithms. A distinct data block size, usually consisting of 64 bits, is transformed into another distinct-size block. Key size, block size and the number of rounds are convertible and variable in RC5 ciphers. RC5 uses key encryption and decryption as well as key expansion.
Techopedia explains RC5
In 1994, Ronald Rivest designed RC5 for RSA Security. RC5 has a variable number of rounds ranging from 0 to 255 with block size bits of 32, 64 or 128. Keys can range from 0 to 2040 bits. Users can choose between rounds, block sizes and keys. When the output and input blocks and the keys are all the same size, an RC5 block can match the same number of block sizes from permutations to integers. RC5 is known for its technical flexibility and the security it provides.