# HT Editor Documentation

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### HT Editor

This is HT 2.0.19; Have fun...

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### About

This program is a file viewer, editor and analyzer for text, binary, and (especially) executable files.

> This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.

> This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

> You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111 USA

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### Key bindings

- General key bindings

  Return | follow link (if applicable)
  Backspace | undo “follow link”
  Space/F6 | choose view mode
  Alt+[1-9] | select window
  Alt+0 | select window list
  Ctrl+Left/Right | scroll left/right
  Cursor keys | move around
  Page Up/Down | next/prev page
  Alt+S | toggle select
  Ctrl+Ins/Alt+C | copy
  Shift+Ins/Alt+V | insert
  Ctrl+Del/Alt+D | delete
  Shift+Del/Alt+X | cut

- Window key bindings

  Alt+F3/Ctrl+W | close window
  Ctrl+F5 | resize/move mode
  | (in resize/move mode only:)
  Space | toggle resize/move mode
  Cursor keys | resize/move window
  Escape/Return/Ctrl+F5 | leave resize/move mode

- Analyser key bindings

  c | continue code analysis at cursor
  f | follow dword ptr at address
  n | name current address (empty string to delete)
  x | show xrefs (search for xrefs)
  # | edit comments
  s | define a string
  i | define an integer (32bit)
  h | define a halfword (16bit)
  b | define a byte (8bit)
  Ctrl+A | call assembler
  Ctrl+F | goto start of current function (indicated in the 2nd line)
  Ctrl+L | goto previous label
  Ctrl+T | show recursive function references

Note: Some keys don't work in HT-posix. Try using Escape instead of Control or something...

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### Authors

- Stefan Weyergraf
- Sebastian Biallas sb@biallas.net

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### Features

HT contains some very advanced and useful features, which you should carefully inspect:

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### General features

1. Supported file formats
   - common object file format (COFF/XCOFF32)
     - - header
       - image with code/data analyser (x86)
   - executable and linkable format (ELF)
     - - header
       - section headers
       - program headers
       - symbol tables
       - image with code/data analyser (x86, AMD64, IA-64, Alpha, PowerPC, ARM) and relocations
   - linear executables (LE)
     - - header
       - VxD descriptor
       - object table
       - page table
       - image with code/data analyser (x86)
       - auto-relocation layer (only internal refs for now)
   - standard dos executables (MZ)
     - - header
       - relocations
       - image (disassembly only)
   - new executables (NE)
     - - header
       - segments
       - names
       - entrypoints
       - image with code/data analyser (x86)
       - auto-relocation layer (pretty complete)
   - portable executables (PE32, PE64)
     - - header
       - import section
       - delay-import section
       - export section
       - resources
       - image with code/data analyser (x86, AMD64, PowerPC, IA-64, Alpha, ARM)
       - preliminary support for .net executables
   - java class files (CLASS)
     - - header
       - image with code/data analyser (java bytecode disassembler)
   - Mach exe/link format (MachO)
     - - header
       - image with code/data analyser (x86, AMD64, PowerPC, ARM)
   - X-Box executable (XBE)
     - - header
       - imports
       - image with code/data analyser (x86)
   - Flat (FLT)
     - - header
       - image with data analyser (no disassembler yet)
   - PowerPC executable format (PEF)
     - - header
       - imports - image with code/data analyser (PowerPC)
   - Still some to be implemented (M$-OBJ, ARCH, LX)
2. Code & Data Analyser
   - finds branch sources and destinations recursively
   - finds procedure entries
   - creates labels based on this information
   - creates xref information
   - allows to interactively analyse unexplored code (press 'c')
   - allows to create/rename/delete labels (press 'n')
   - allows to create/edit comments (press '#')
3. Target systems
   - DJGPP
   - GNU/Linux
   - FreeBSD
   - Win32

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### Configuration files

#### Global configuration

HT automatically creates a file to store its configuration. It is called `~/.htcfg2` on Unices and `ht.cfg2` (where ht.exe resides) on Windows. More specifically it contains HT's registry and the See Global history.

#### Per file configuration

The analyser (for analysable files) will be stored in an extra file called `FILENAME.htcfg`, where FILENAME is the analysed file. This file contains all information to restore the complete state of the analyser.

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### Clipboard

All open files and dialogs use the common clipboard, where all copied and cut text or binary data is stored. Clipboard operations are normally binary safe, that means you can copy some binary data out of a file and paste it into an input line. Exceptions are only the \0 character (binary null), it will be converted to a space in places where it would not make sense (e.g. file open).

Although the clipboard won't be saved between different HT sessions (ie. you will loose it when exiting HT), you can either save and load it or part of it manually (via Edit->paste into/copy from file) or rely on the input lines' See history, which is stored and retrieved from the config file automatically.

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### Global history

HTs history system is global, which means that you can use it for all open files. Histories are also grouped by their context. I.e. file-related and regex-search-related dialogs have their own history (who would want to open "[0-9][0-9a-z]+" anyway?).

History entries are stored within the See Configuration files, so they can be reused when you relaunch.

You can delete a history entry by pressing DEL inside the history popup.

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### Expression evaluation

HT contains a very powerful expression evaluator which is used in all dialogs where expressions are expected. These are mainly blockoperation, goto, search and of course evaluate itself (Edit->Evaluate).

You can use all standard math operators (+ - / * % **), logical operators (! && || ^^), relational operators (== != < > <= >=), bit operators (~ & | ^), string operators (. for concatenation), parenthesis, the ternary operator (a?b:c), functions and symbols (both depending on context).

The evaluator uses integer, string and float types depending on context. You can always convert a result via the `int()`, `string()` and `float()` functions to appropriate type. Try Edit->Evaluate to see how it works...

#### Functions and symbols

You can always use the standard built-in math (`round`, `sin`, `random`, etc.) and string (`strcmp`, `strchr`, `sprintf`, etc.) functions, they work more or less like the corresponding C functions (actually they ARE more or less wrappers for them); see `eval/eval.y` for details (sorry but a detailed help would get outdated rather soon).

The symbol _ always refers to the last result.

When using See Block operations, or searching you have some context depending functions and symbols; see these sections for explanation.

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### Block operations

Block operation (Blockop) is a very powerful tool to perform modifications on binary files. It is available in hex viewer only.

Blockop takes four parameters: start, end, mode and expression. Blockop works as follows:

- START: Start at the offset specified by start
- REPEAT: Evaluate expression and store n bytes (1 - byte, 2 - word, 4 - dword, variable - string) at the current offset. Increment current offset by n. Stop if end has been reached.

Special variables/functions that can be used in expression:

`readbyte(ofs)`
  read a byte from offset ofs, returns a number
`readstring(ofs, size)`
  read size bytes from offset ofs, returns a string
`i`
  contains the iteration count/index starting with 0
`o`
  contains the current offset

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### Search and its different modes

The search function is one of the most advanced functions of HT. It is invoked through F7, Shift-F7 continues a search from cursor. Depending on context (ie. file type and mode) the following modes are enabled:

#### bin: ASCII / Hex

Enter an exact search string either via ascii characters or via hexadecimal interpretation. This is the fastest search mode. You may specify a case-insensitive search.

#### bin: eval str

Enter an expression, it will be evaluated ONCE (difference to the 4th mode), and HT will then search for the result-string. This is pretty useful when searching for intermixed text and control-chars/binary, e.g. `"hello world\n\0"`

#### display: regex

As the prefix indicates, this search doesn't search in the binary file but in the display on screen. HT searches for a regular expression so this can be very powerful, e.g. in PE/Image you can search for `(add|sub).+?,\ [78]$`. This will find all add or sub instructions with second parameter 7 or 8.

#### expr nonzero

This is the slowest but also most advanced search mode. Enter an expression and the search stops if this expression evaluates to non-zero (it will be evaluated on every byte). In this mode there are two predefined symbols and some functions: i is always the number of current iteration and o stands for the current offset in file. With the functions `readbyte(ofs)` and `readstring(ofs, size)` you access the file's content.

It's easier to understand this with examples:

1. Searching for patterns:
   1. Enter `readbyte(o) == readbyte(o+1)`
      This will search for two equal bytes ("AA", "55", "!!", etc.).
   2. Enter `(readbyte(o) == readbyte(o+1)-1) && (readbyte(o)==readbyte(o+2)-2)`
      This will search for three ascending bytes ("ABC", "123", etc).
2. Search with special functions:

   With HT you can easily detect the RSA key in the `ADVAPI32.DLL`: Search for `entropy(readstring(o, 64)) > 82` in expr!=0 mode, and you will find it very quickly. How does it work? `readstring(o, 64)` reads a 64 byte string from current offset and entropy calculates the entropy ("randomness") of a string (result is 0..100). So the search stops if a entropy greater than 82% (guessed value) is encountered, which normally indicates packed or encryted data.

   Note: the `entropy()` function is not the best of its kind, if you know of a better one please let us know!

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### Command line options

`--` |  | treat all additional parameters as file names
`-v` | `--version` | show version and copyright on console
`-h` | `--help` | show help
`-t` | `--text` | load file(s) in text editor mode
`-b` | `--bin` | load file(s) in hex editor mode
`-a` | `--auto` | try to guess file type

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### Where to download?

The HT homepage is located at http://hte.sourceforge.net

Downloads are available from the 'download' section. Please also take a look at http://sourceforge.net/projects/hte