variable string length in 3des algorithm

[prathibha]

Hi,

I am doing cryptography using 3des algorithm, i tried the algorithm with string length as 24. If i pass the string which is more or less than 24 length then it will crash throwing exception. If i pass string with 24 length it is fine work.

And can anyone tell me what should be the keysize of 3des?can we change the key size?can we change the string size?if so how can i do these things. please tell me