Defining an External Mode===========================To define an external cracking mode you need to create a configuration filesection called [List.External:MODE], where MODE is any identifier that youassign to the mode. The section should contain some functions coded in asubset of the C language. John will compile and use them if you enable thismode via the command line. External Functions--------------------The following functions are currently used by John:init()		called at startup, should initialize global variablesfilter()	called for each word to be tried, can filter some words outgenerate()	called to generate words, when no other cracking modes usedrestore()	called when restoring an interrupted sessionAll of them are of type 'void', with no arguments, and should use globalvariable 'word' (pre-defined as 'int word[]'), except for init() which iscalled before 'word' is initialized. The 'word' variable contains currentword to be tried, in ASCIIZ.The functions, if defined, should do the following with 'word':* filter() can modify the word, or zero out 'word[0]' to skip it;* generate() shouldn't assume any particular value of 'word' when it getscalled, but should set it to the next word to be tried, or zero out'word[0]' when cracking is complete (this will cause John to terminate);* restore() should set global variables to continue from the 'word'.You can use an external mode separately, or with some other cracking mode,in which case only init() and filter() will be used (and only filter()will be required). Using an external filter is compatible with all theother cracking modes and '-makechars' command line option.It is recommended that you don't use filter(), or at least don't filtertoo many words out when using an external mode with your own generate().Better modify generate() not to generate words that would get filtered out. The Language--------------As I already mentioned above, the compiler supports a subset of C. John isa cracker, not a compiler, so I don't think it needs anything else. (Well,I'm not even sure it needed a compiler at all, but using an external, say,perl is less convenient in some cases...)Here's a list of supported keywords: void, int, if, else, while, continue,break, return. You can define standard functions to be called by John,define global and local variables (including single dimensional arrays),use all the integer operations supported in C, and use C comments.The following C features are missing in John's compiler:* only standard functions supported, you can't define your own ones;* only 'while' loops are supported;* only 'int' and 'void' data types supported;* only single dimensional arrays supported;* structs/unions are not supported;* pointers are not supported (array name refers to the first element);* probably something else...You can find some external mode examples in the default configuration filesupplied with John.