BIOS

CTF-Challenges

Challenge 1

Multi Encoder

CHALLENGE DESCRIPTION

Its all about the base

Flag format - inctfj{flag_here}

Approach

I solved this challenge using the basic Linux commands. Initially I checked what is in the file given along with the task it is encoded text file using hex and binary also a python file explaining the encryption pattern. Then I checked the python file I found that it's encrypted the file 5 times So then I took that encrypted file I understood that it is a hex encoded file then I used the following command to decode hex: cat ciper.txt| xxd -r -p | base64

In this the xxd -r -p it will convert them into binary afterwards it is encoded to base64 and stored to another txt file called ciper2.txt.

Then I decoded the base64 encoded file using the following command:

cat ciper2.txt | base64 --decode

it will decode the base64 encoded text.

I changed the content of txt file after each decryption.

I repeated this two commands several times to find the flag. Its not sure But I remember that if I am decoding hex once. I have to decode Base64 twice I repeated this several times and I found the flag.

Challenge 2

base-base-base

CHALLENGE DESCRIPTION

Have you heard of bases? I heard combination of those can be really cool!

Approach

In this task I solved with basic Linux commands. There is a text file attached to the file which contain the encoded text. When I opened the file I found the text is encoded with base 64 and I Used the following command to decode the base 64:

echo "encoded text" | base64 --decode

When it decoded it was found that the output text is encoded with base32 so I used following command to decode the base32 encoded text:

echo "encoded text" | base32 --decode

When it decoded it is found that the output text is encode with hex so afterwards I converted the hex to base64 for that I used the following command:

echo "hex encoded text" | xxd -r -p | base64

Then It will decode hex to base64 format Then I decoded the base64 encoded text using the following command:

echo "encoded text" | base64 --decode

After encoding the base64 I found he flag.

Challenge 3

Single byte X0r

CHALLENGE DESCRIPTION

Given a hex encoded string: 1314190e1c1001024a0825194e145d0e251849251f4e091316032518084a11491407 The above string has been Xored against a single character 'z'. Decode it to a meaningful sentence and get the flag.

Approach

When I opened the task found a cipher text provided and found that it has been xored against a single character z. we just need to xor it again with the same key to get the flag.

Challenge 4

Naïve Cipher

CHALLENGE DESCRIPTION

This Cipher is a very simple and common encryption method which forms part of the basis of cryptography. It simply shifts a string of letters a certain number of positions up or down the alphabet.

encoded string: dixoae{oczz_ocz_hvnozm_ja_xvznzm_xdkczm}

Approach

When I opened I found the encoded text and the text has been shifted with the key -5 by comparing the original flag to the text given .So we just decrypt it using this info.

Challenge 5

Angry Steve

CHALLENGE DESCRIPTION

Jimmy found out about an embaraasing picture of his dad Steve. He believes that there is a text inside that file somwhere. But he is too scared to open and tamper with it as his father is a very short tempered man. Help Jimmy out!.

Approach

I saw one image file attached to this task I downloaded it and found that some strings and unprintable character in it I used the following Linux command to find the flag.

Strings Angry.jpg | grep "inctf"

In this I used the string for extracting all the printable characters from the image file and used grep is used to search the keyword inctf from the specified file. Then I found the flag

Challenge 6

Mischief Kid

CHALLENGE DESCRIPTION

Little Bart here is the biggest troublemaker in town. He is hiding the flag somewhere safe. Follow and bust out little Bart to get what you want!

Approach

I found a zip file attached to the task. I downloaded the file and extract the file in it I found a image file in it some files are hided. So I tried to unzip that image file it extracted the files

In it I found one unsupported image file and a text file so I converted the text file into image file then I used a external tool called the ghex and I compared the hex of both image file then I found some are missing in one or them I added those and opened the image in it I found the flag.

Challenge 7

Snow Man

CHALLENGE DESCRIPTION

Read the challenge name again! And yeah, everything you need is present in this file.

Approach

I found a text file in attached to the task. I stored the content in a flag.txt. When I read the text I understood the password is thisiseasy I used an external tool called stegsnow the following command will help to find out the flag in base64 format:

Stegsnow -C -p 'thisiseasy' flag .txt

Then I found the base64 encoded text Then I decoded the base64 code using the following command to get the flag.

echo "encoded text" | base64 –decode