PicoCTF 2017 – computeAES #infosec #appsec #crypto #ctf

Another day, another challenge.

Today’s blog post will explore solving the “computeAES” challenge in PicoCTF.

Let’s get started.

Clicking on the challenge we see the following:

PicoCTF_computeAES_1

Clicking on the clue link we see the following:

PicoCTF_computeAES_2

Going back to the challenge and clicking the hints we see:

PicoCTF_computeAES_3

Let’s use the hint of using online tools to solve this challenge.

Doing a Google search for “convert base64 to hex” we get the following link.

Going to this link we put in our base64 input to get the hex equivalent.

Doing this for the key and the input we get the following:

Key = 4f9b95cd8b6e04dbfabf08e886c955e3

Input = b75874a9b70e851405e44e3a6ec34b8a67db708e9e82b28fe0b1ed291de54f851d5a386cb0cf11412053ed2ffcadc472

Doing another Google search for “AES calc hex” we get the following link.

Entering the hex value of the key and input we get the following:

PicoCTF_computeAES_4

We found the flag! Copying the flag and removing the extra space we’ve acquired 50 points!

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PicoCTF 2017 – Yarn #appsec #infosec #ctf

Another day, another challenge…

Today’s blog post we will solve the, “Yarn” challenge from PicoCTF.

Let’s get started.

Clicking on the challenge we see:

PicoCTF_Yarn_1

OK, we need to find a flag inside of a file, but we do not know what the file is.

Let’s look at the hints and see if that provides any clues.

PicoCTF_Yarn_2

Looking at the hints we’re provided with two questions. Possibly answering these questions will leads us to the flag.

Answer question #1 – “what does the string command use to determine if something is a string?” We decide to do a Google search to answer just that.

Doing this Google search we’re provided with the following link.

Reading the article we determine that the strings command prints the printable characters from a file.

Doing that we’re provided with the following screenshot:

PicoCTF_Yarn_3

We’ve answered question #1. Let’s answer question #2.

Question #2 – is there a way to change the length that the strings command look for?

Going back to the link we see that there is a way we can specify that there is a way to determine the length of strings we want to print.

How do we use this?

By adding the “-n <length you want to use>”

Doing this we get the following:

PicoCTF_Yarn_4

Scrolling down we see:

PicoCTF_Yarn_5

Hmm… I think we found the flag! “Submit_me_for_I_am_the_flag”

Putting this string as the flag we have acquired 55 points!

PicoCTF 2017 – Hash101

Another day, another challenge.

Today’s blog post will be solving the “Hash101” challenge from the PicoCTF.

Let’s get started.

Clicking on the challenge we see…

PicoCTF_Hash101_1

OK we need to hashes to claim our flag. Let’s see what the hints say.

PicoCTF_Hash101_2

Looking at the hints Google will be our friend 🙂

Connecting to the server we see:

PicoCTF_Hash101_3

We need to convert the binary to ASCII text.

Doing a Google search of, “binary to ASCII text converter” search we get the following website.

Going there, we see:

PicoCTF_Hash101_7

Changing the binary to the binary in the challenge we get:

PicoCTF_Hash101_8

The text we’re looking for is “peace” entering this in we are now in the second level of the challenge.

PicoCTF_Hash101_11

We need to find the hex value of our word, peace. Going back to the link referenced above, we see that the hex is referenced.

PicoCTF_Hash101_12

Entering that we now need to enter the decimal equivalent. For this, going back to Google and entering “hex to decimal converter” we get the following link.

Clicking the link we see:

PicoCTF_Hash101_9

Entering the hex value we get the following decimal value.

PicoCTF_Hash101_10

Entering that into the challenge we get the following:

PicoCTF_Hash101_13

Going to the third level we see:

PicoCTF_Hash101_14

Reading the description one might ask, what are we looking for?

Remember from the first level of the challenge where we need to find the ASCII text?

Doing a Google search of, “ASCII table” we find the following link.

Opening the link we see the ASCII equivalent of the letters.

We need to find a string that when doing the modulo of base 16 we get a number of 10.

One might wonder… what is modulo?

The modulo is the remainder of a division equation.

We know that we are dividing by 16 and the modulo (remainder) needs to be 10.

One way to achieve this is to find any multiple of 16 and add 10.

Why multiple of 16? Doing a multiple of 16 if we did a modulo of that the modulo would be 0 (as there is no remainder).

Doing this I was able to do the following:

PicoCTF_Hash101_5

Entering 4, we had a module of 4 and not 10.

Entering the string of “:” we were able to complete the level. Why? “:” in ASCII is 58. How did we get 58? 16 * 3  = 48 + 10 = 58. We’re adding 10 because we know we need a remainder of 10.

Moving to level 4 we see:

PicoCTF_Hash101_15

Doing another Google search of, “MD5 decrypter” we get the following link.

Clicking the link and entering the md5 hash, we get the following:

PicoCTF_Hash101_16

Entering this the level we see:

PicoCTF_Hash101_17

Entering this flag into the input box we’ve acquired 50 points!

PicoCTF 2017 – LeakedHashes

Another day, another challenge…

Today’s blog post we’re going to solve the “LeakedHashes” challenge from PicoCTF.

Let’s get started.

Clicking on the challenge we see:

PicoCTF_Leaked_Hashes_1

OK – we need to log into a service, but we do not know the password. We do have leaked hash passwords.

Clicking the hashdump.txt file we see:

PicoCTF_Leaked_Hashes_2

Let’s see what the hints say.

PicoCTF_Leaked_Hashes_3

OK. Let’s see if we can find a way to crack these passwords!

Doing a Google search for “online cracked hashes” we get the following link.

Trying the first hash of root we were not able to crack the password.

Using the second hash of christene, we get:

PicoCTF_Leaked_Hashes_4

We were able to crack the password.

Let’s try to login in with christene.

Going back to the commnd line and using the nc command we get:

PicoCTF_Leaked_Hashes_5

Scrolling down we see:
PicoCTF_Leaked_Hashes_6

We found the flag, and acquired 90 points!!!

PicoCTF 2017 – Mystery Box

Another day, another challenge.

In today’s blog post we will be solving the “Mystery Box” challenge from the PicoCTF.

Let’s get started.

Clicking on the challenge we see:

PicoCTF_Mystery_Box_1

OK, we have a mystery machine, with a stick note, and a picture.

Clicking on the sticky note link we see:
PicoCTF_Mystery_Box_2

OK… we have a note. This is going to be useful later.

Clicking on the picture link we see:

PicoCTF_Mystery_Box_3

Going back to the challenge and click on the hints we see:

PicoCTF_Mystery_Box_4

OK. The hints tell us that this box uses gear and it was used from the naval services. Also we have the name of Turing… let’s see what Google would provide us.

Doing a Google search of “Turing machine naval” we get the following link.

This link is the enigma machine emulator.

The enigma machine was used in WW2 (World War 2) to help crack secret messages from Nazi Germany.

The person who was responsible for this machine was Alan Turing. Alan Turing was the father of computer science. He was a computer scientist, mathematician, logician, etc. If you want to read more about his life, click here.

Going back to the enigma machine emulator we see:

PicoCTF_Mystery_Box_5

Hmm… we see that the words are similar to are listed in the note.

Let’s use that to figure out what the enigma machine will return us.

After entering the information we get:

PicoCTF_Mystery_Box_6

Hmm… The enigma machine returned – “quite puzzling indeed”.

Putting this in as the flag, we acquired 60 points!!

PicoCTF 2017 – Hex2Raw

Another day, another challenge…

Today’s challenge we will be solving the Hex2Raw challenge in the PicoCTF.

Let’s start.

Clicking on the challenge we see the following:

PicoCTF_Hex2Raw_1

OK. With this challenge we see that we need to print unprintable characters from the following location.

Let’s see what the hints give us.

Clicking on the hints we see:

PicoCTF_Hex2Raw_2

OK. We can see that Google has easy techniques to do this.

Let’s go to the command line and see what we can do.

After logging in and going to the directory we see the following:

PicoCTF_Hex2Raw_3

Running the hex2raw application we see:

PicoCTF_Hex2Raw_4

I pressed Ctrl + C to end the program.

OK. We are given raw input and we need to convert it to hexadecimal character.

Doing a Google search we noticed that we can use Python to get our desired output.

How would we do this?

With the decode function!

PicoCTF_Hex2Raw_5

Explaining the screenshot below we’re invoking the python interpreter the -c designated that we’re using a command. We’re printing the raw form, and using the decode function designated that we wanted to decode with the hexadecimal system. We’re going to pipe the output to the hex2raw program.

Doing this we see the flag, and acquired 20 points!

PicoCTF 2017 – Just No

Another day, another challenge…

Today’s blog post we’re going to solve the “Just No” challenge in the PicoCTF challenge.

Let’s start.

PicoCTF_Just_No_1

OK… we have a program that has access to the flag, but refuse to give it to us.

Let’s look at the hints and see what we can do.

PicoCTF_Just_No_2

OK.. we need to look at the absolute and relative paths, and spoof the file that the program is looking for.

Let’s go to the program.

After clicking logging into the command line and navigating to the folder we see the following:

PicoCTF_Just_No_3

Opening the auth file with the cat command we see:

PicoCTF_Just_No_4

OK. The file only as no. Let’s see how this is being used.

Opening the justno.c file with the cat command we see:

PicoCTF_Just_No_5

Reading the file we see we’re opening the auth file and determining if the the auth file does not have the word “no”. If that’s true then we’re presented with the flag. If the auth file does contain the word “no” then we go inside the else block which print, “auth file says no. So no. Just… no.”

As we can see when we opened the auth file it currently has the word “no”. Which means if we executed the justno program right now we would go to the else block, and receive the no message.

Now is the time to utilize the hints. We need to spoof the auth file to be ANY word except for no. How are we going to do this?

Well the challenge told us to read the difference between absolute and relative paths. Once we figured that out, then we can create a new auth file and point it to the new location.

Let’s give it a shot.

Going back to the justno.c we see that the file open is using relative paths.

We can spoof the location by creating the file structure and then calling the justno.c program and printing the flag.

Let’s do it.

PicoCTF_Just_No_6

Looking at the screenshot you can see we created the same directory structure and created a new auth file that was listed in the justno.c program. Once we did that and called the justno program again we were able to get the flag and acquired 40 points!