not be freed.
SRP_check_known_gN_param() returns the text representation of the group id
-(ie. the prime bit size) or NULL if the arguments are not valid SRP group parameters.
+(i.e. the prime bit size) or NULL if the arguments are not valid SRP group parameters.
This value should not be freed.
SRP_get_default_gN() returns NULL if I<id> is not a valid group size,