jquery password problem

I encode my password with md5 base 64 ..on the php side but i have a problem with the POST that this function i using on my form. after posting my data + is replaced with space I came out with that explanation after a lot of tries and echos in my code files i found out that after using numbers ,onlu on that case, in the password field the space between the encoding was replaced with a + or / sometimes i tried to remove the + or / but still i get the same results any ideas data: "firstname="+ firstname +"& lastname="+ lastname +"& username="+ username +"& email="+ email +"& password="+ password +"& save="+ save+"& user_type="+ user_type,