Cracking Mode

External Mode

External mode allows you to plug in custom password generation code written in a C-like scripting language. It is for advanced users who need algorithms beyond John's built-in modes — for example, generating passwords from specific patterns, implementing custom hash append/prepend logic, or deriving candidates from contextual information like a target's pet names or employee lists.

External modules are shared C code compiled into John or loaded at runtime. The Jumbo distribution ships with many pre-built external modes for common scenario variations.

When to Use External Mode

1

Custom Pattern Cracking

You know the password pattern (e.g., "CompanyName" + 2-4 digits + special char) and need to generate only that structure.

2

Hybrid Dictionary+Transform

Combine two wordlists (first name + last name) or apply transforms based on external data sources.

3

Context-Aware Generation

Passwords derived from specific domain knowledge: product codes, internal jargon, employee IDs.

4

Algorithmic Bruteforce

Generate passwords according to a mathematical sequence or encoding that rules cannot achieve.

Usage

Use a built-in external mode

bash
1john --external=Alnum4 hashes.txt

Alnum4 generates all 4-character alphanumeric combinations; useful for short PINs.

List available external mode formats

bash
1john --list=external

Combine with wordlist

bash
1john --wordlist=names.txt --external=MyMutator hashes.txt

Common Built-in External Modes

AlnumN

N-character alphanumeric brute force.

LowerN

N-character lowercase brute force.

Mask

Pattern-based with placeholders (e.g., ?y?y?d?d?d).

Kstats

Keyboard patterns for keywalk attacks.

DigitsN

N-digit PIN brute force.

dMOF

Custom format output for certain hash modules.

Regex

Generate candidates matching a regular expression.

Python

Embedded Python scripting (if built with Python support).

Creating Custom External Modes

External modes are C functions compiled into a shared library (.so) that John loads. This is an advanced topic requiring C knowledge and John source familiarity.

Basic skeleton (external_MyMode.c):
#include "external.h"
#include "memory.h"

extern char *password;
extern int eaindex, eacount;

void init() {
  // Initialize your generator state
}

void generate() {
  // Set 'password' to the next candidate
  // Use get_next_*() functions from external.h
}

void restrict() {
  // Optional: implement charset restrictions
}

Warning

Writing external modes requires building John from source and familiarity with C programming. Most users should stick to --rules and --incremental.
Next: Hash Formats Back