BF_cbc_encrypt() operates of data that is a multiple of 8 bytes long, while
BF_cfb64_encrypt() and BF_ofb64_encrypt() are used to encrypt an variable
number of bytes (the amount does not have to be an exact multiple of 8). The
purpose of the latter two is to simulate stream ciphers, and therefore, they
need the parameter B<num>, which is a pointer to an integer where the current
offset in B<ivec> is stored between calls. This integer must be initialised
BF_cbc_encrypt() operates of data that is a multiple of 8 bytes long, while
BF_cfb64_encrypt() and BF_ofb64_encrypt() are used to encrypt an variable
number of bytes (the amount does not have to be an exact multiple of 8). The
purpose of the latter two is to simulate stream ciphers, and therefore, they
need the parameter B<num>, which is a pointer to an integer where the current
offset in B<ivec> is stored between calls. This integer must be initialised