Constructor that takes number of bits to use.
RIPEMD-256 and RIPEMD-320 are optional extensions of, respectively, RIPEMD-128 and RIPEMD-160, and are intended for applications of hash functions that require a longer hash result without needing a larger security level.
Some applications of hash functions require a longer hash result without needing a larger security level. To this end RIPEMD-256 and RIPEMD-320 are constructed from, respectively, RIPEMD-128 and RIPEMD-160 by initialising the two parallel lines with different initial values, omitting the combination of the two lines at the end of every application of the compression function, and exchanging a chaining variable between the 2 parallel lines after each round. Remark that the security level of the 320-bit extension of RIPEMD-160 is only guaranteed to be the same as that of RIPEMD-160 itself, and similarly for the 256-bit extension of RIPEMD-128 with respect to RIPEMD-128 itself.