Copy Link

Add to Bookmark

Report

NULL mag Issue 03 17 Hex editing with DD

eZine lover (@eZine)

Published in

· 26 Dec 2020

  

https://www.rationallyparanoid.com/articles/dd-hex-editor.html 
How to use dd as a hex editor                                 April 13, 2010 

WARNING: All commands should be tested first or performed on copies of the  
files using an account with minimal privileges. A slip-up while using dd with  
a root account can have a significant impact on your system. Author is not  
liable for any damages resulting from inaccuracies or mistakes within this  
page. 

dd can be used much like a hex editor to perform low-level file-content  
editing, but through a command-line instead of a GUI. This can be useful in  
cases where you have shell access to a system and need to edit binary files  
on the spot. 

In this tutorial the target file will be a 64 byte block of null characters  
called "64zero". Its contents is the following: 

user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

We will also use 2 input files. One called a.txt that consists of 16 bytes of  
the ASCII value A: 

user@linux:~$ xxd a.txt 
0000000: 4141 4141 4141 4141 4141 4141 4141 4141 AAAAAAAAAAAAAAAA 

And the other called b.txt which is a 16 byte string of the ASCII values  
A to P: 

user@linux:~$ xxd b.txt 
0000000: 4142 4344 4546 4748 494a 4b4c 4d4e 4f50 ABCDEFGHIJKLMNOP 

In every example we will show you the command required to perform the desired  
action, and demonstrate the results. Although it is not as efficient from a  
performance perspective, a block size of 1 is specified in each example for  
the sake of simplicity. 

Overwrite 1 byte of data in target file 64zero at offset 0 (i.e. the beginning 
of the file) with random data: 

user@linux:~$ dd if=/dev/urandom count=1 bs=1 of=64zero conv=notrunc 
1+0 records in 
1+0 records out 
user@linux:~$ xxd 64zero 
0000000: 5200 0000 0000 0000 0000 0000 0000 0000 R............... 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite 1 byte of data in target file 64zero at offset 8 with random data: 

user@linux:~$ dd if=/dev/urandom count=1 bs=1 seek=8 of=64zero conv=notrunc 
1+0 records in 
1+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 d500 0000 0000 0000 ................ 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite 4 bytes of data in target file 64zero starting at offset 8 with  
random data: 

user@linux:~$ dd if=/dev/urandom count=4 bs=1 seek=8 of=64zero conv=notrunc 
4+0 records in 
4+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 edd7 0128 0000 0000 ...........(.... 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite 4 bytes of data in target file 64zero starting at offset 8 with the  
contents of a.txt: 

user@linux:~$ dd if=a.txt count=4 bs=1 seek=8 of=64zero conv=notrunc 
4+0 records in 
4+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 4141 4141 0000 0000 ........AAAA.... 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite data in target file 64zero starting at offset 8 with the entire  
contents of a.txt: 

user@linux:~$ dd if=a.txt bs=1 seek=8 of=64zero conv=notrunc 
16+0 records in 
16+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 4141 4141 4141 4141 ........AAAAAAAA 
0000010: 4141 4141 4141 4141 0000 0000 0000 0000 AAAAAAAA........ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite data in target file 64zero starting at offset 0 with the entire  
contents of a.txt: 

user@linux:~$ dd if=a.txt of=64zero conv=notrunc 
0+1 records in 
0+1 records out 
user@linux:~$ xxd 64zero 
0000000: 4141 4141 4141 4141 4141 4141 4141 4141 AAAAAAAAAAAAAAAA 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite data in target file 64zero starting at offset 8 with 1 byte of b.txt  
after skipping the first 3 bytes of b.txt: 

user@linux:~$ dd if=b.txt skip=3 seek=8 bs=1 count=1 of=64zero conv=notrunc 
1+0 records in 
1+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 4400 0000 0000 0000 ........D....... 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Overwrite data in target file 64zero starting at offset 8 with 2 byte of b.txt 
after skipping the first 3 bytes of b.txt: 

user@linux:~$ dd if=b.txt skip=3 seek=8 bs=1 count=2 of=64zero conv=notrunc 
2+0 records in 
2+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 4445 0000 0000 0000 ........DE...... 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 

 
Append entire contents of b.txt to the end of target file 64zero: 

user@linux:~$ dd if=b.txt of=64zero oflag=append conv=notrunc 
0+1 records in 
0+1 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000040: 4142 4344 4546 4748 494a 4b4c 4d4e 4f50 ABCDEFGHIJKLMNOP 

 
Overwrite data in the target file 64zero starting at offset 16 with entire  
contents of b.txt. Truncate the output file: 

user@linux:~$ dd if=b.txt seek=16 bs=1 of=64zero 
16+0 records in 
16+0 records out 
user@linux:~$ xxd 64zero 
0000000: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 
0000010: 4142 4344 4546 4748 494a 4b4c 4d4e 4f50 ABCDEFGHIJKLMNOP

Share this article

Share on Twitter / X

Share on Facebook

Share on WhatsApp

Share on Telegram

Share on Reddit

Share on LinkedIN

sending ...

New to Neperos ? Sign Up for free

download Neperos App from Google Play

install Neperos as PWA

Let's discover also

Cryptel's journal picture

Cryptel Issue 01

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 02 08 Old emags and NULL mag...

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 07 23 Null logo 2

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 07 22 Null logo

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 08 30 Null logo

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 05 03 About the mag

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 02 03 About the mag

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 03 03 About the mag

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 04 03 About the mag

@eZine • 3 years ago

null magazine's journal picture

NULL mag Issue 05 12 Explaining ansi removal from the mag

@eZine • 3 years ago

Recent Articles

Was Khambat the oldest civilization in the world?

Was Khambat the oldest civilization in the world?

@lostcivilizations • 1 hour ago

Migrations and human demography from the origins to the 21st century

Migrations and human demography from the origins to the 21st century

@lostcivilizations • 1 hour ago

Marcahuasi's secret

Marcahuasi's secret

@lostcivilizations • 3 hours ago

The esoteric chronology of Daniel Ruzo, the great scholar of Marcahuasi

The esoteric chronology of Daniel Ruzo, the great scholar of Marcahuasi

@lostcivilizations • 3 hours ago

The origin of the American man: the enigma of Pedra Furada

The origin of the American man: the enigma of Pedra Furada

@lostcivilizations • 5 hours ago

Rose and Pistachio Milk Cake

Rose and Pistachio Milk Cake

Sweet Desserts and Baking

@AniphaeS • 10 hours ago

Samoa Cheesecake

Samoa Cheesecake

Sweet Desserts and Baking

@AniphaeS • 15 hours ago

Pistachio Mousse Cheesecake

Pistachio Mousse Cheesecake

Sweet Desserts and Baking

@AniphaeS • 15 hours ago

No-Bake Peanut Butter Pie

No-Bake Peanut Butter Pie

Sweet Desserts and Baking

@AniphaeS • 15 hours ago

3-INGREDIENT NO FLOUR CHOCOLATE CAKE

3-INGREDIENT NO FLOUR CHOCOLATE CAKE

Sweet Desserts and Baking

@AniphaeS • 15 hours ago

Recent Comments

eZine lover (@eZine)

you are welcome :)

eZine lover (@eZine)

These files were released in the 80s and 90s on BBSs, ancient ancestors of the modern internet. This file in particular dates back to Octobe ...

eZine lover (@eZine)

eZine lover (@eZine)

Thank you. Old ezines need to be preserved

this tutorial is from 2006, completely useless today. where do I find the software mentioned in it?

thanks for sharing

Rainbow Six was a great game. I prefer the playstation version

Where did you find it?

Lost Civilizations (@lostcivilizations)

Thank you for posting this old digest :)

Doom was my favorite game. I have played it for years and created a lot of customs levels.

Neperos cookies

This website uses cookies to store your preferences and improve the service. Cookies authorization will allow me and / or my partners to process personal data such as browsing behaviour.

By pressing OK you agree to the Terms of Service and acknowledge the Privacy Policy

By pressing REJECT you will be able to continue to use Neperos (like read articles or write comments) but some important cookies will not be set. This may affect certain features and functions of the platform.

OK

REJECT