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So you want to decode...

This is an intro on how one can start getting into decoding games. While there are plenty of helpful tools and walkthroughs on the internet, many new decoders can easily become overwhelmed figuring out which tools to use or where to even start when presented with something like IXRuZW1uZXRoZ2lsbkUgZWh0IG5pb0o=. This primer will walk through "how to strategize" when presented with a decoding problem with examples. In the end, you'll have the basic understanding of what's happening that you can then use to try out and learn their vast number of decoding tools available on the internet. How we'll do it:

  1. Learn the two ways encrypted/encoded messages are created.
    1. "Encrypting"
    2. "Encoding"
  2. Recognize/guess starting points when you find an encrypted/encoded message

Then you can use tools such as:

This page has been translated in to:

How to encrypt/encode a message

To figure out how to decode, you first have to know how messages are encoded in the first place. To make things easier, you can think of encoding as some combination of the following 2 processes:

  • Encrypting is taking the message and rearranging or substituting the characters to hide a message. In other words, encrypting keeps the same character set (e.g., ASCII characters a-z A-Z and arabic numerals 0-9) but substitutes one for another or rearranges their order. For example, reversing the order of characters would encrypt hello as olleh. These methods are called ciphers
  • Encoding is kind of the converse of encrypting in that it keeps the message the same, just represents it in a different way. For example, Morse code would encode hello as .... . .-.. .-.. ---. These methods are called codings

That's basically it! To create an encoded/encrypted message, you do some combination of one or more of the above. To decrypt, you just do the opposite. The game then becomes, "how do I recognize if I need to decrypt or decode, and which do I use?" To do that, we first can learn about common encryption and encoding techniques

Common encryption techniques

The following is a quick summary of a few of the basic techniques. Encryption can generally be thought of as one of two techniques: (a) some sort of rearranging of the order and (b) substituting letters for others. Given a message, you can hide its meaning by doing things like:

Rearranging: Reversing the order of characters

hello as olleh

Rearranging: Skip Characters, skip cipher

In a skip cipher you write the message every n characters. So id n=4: abcdefgh becomes aebfcgdh How to easily encrypt: write you message on multiple lines, each with n characters. So, with n=4:

abcd
efgh

Then read the columns, from left to right: ae bf cg dh. To decode, write your message in rows and read down the columns. Here you may have to try different combinations to get it to work, or use something like MultiDec's skip tool to do it for you for many combinations at once. For example: aebfcgdh is written as:

ae
bf
cg
dh

Then reading the columns: abcdefgh

Rearranging: Variants of skip cipher

There are plenty of variants to skip that play games with how many to skip at a time, which is why you'll see many online. For example, you can use a passcode to change n after each character, you have a transposition cipher. You also can change n in a clever way using a rail fence cipher. Also, you don't always have to go from left to right, top to bottom, but the direction can change as well as in a route/path cipher. And there are many, many, more. The point here is that you may need to brute force trying different techniques until one "clicks." Luckily, there are many online tools to try out.

Rearranging: regex.ingress.codes to check if you have a keyword in your text

Sometimes you get a bunch of letters and number but don't know if you are at the final step or what kind of rearrangement is needed. There's a trick you can use! If you have a list of possible words that exist in your code, you can use regular expressions (regex) to search the list of possible keywords that use the letters you have! For examle, in Ingress, daily codes have the format aaa##keyword###aa. You can therefore use regex to see if a keyword is present. List of keywords are matinained at several places (e.g., ingress.codes or their github repository), so you can either download and maintain the list yourself or use an internet appication like regex.ingress.codes. To search using regex, type ^[yourlistofcharacters]{6}$ where you replace the 6 in {6} with the number of letters that will appear in the keyword. More documentation available here from ingress.codes and here from decodeingress.me.

As an example: after decoding and decrypting, you get te68o5erezim2tk8uf and want to know if there's a keyword in it. There are 5 numbers, so it matches the format. There are 13 letters, 5 of which are part of the prefix and suffix, so the keyword is 8 letters long. We therefore enter ^[te68o5erezim2tk8uf]{8}$ in to regex.ingress.codes. It will find all keywords that are 8 characters long and are made up only of the letters in our text string. The result: timezero. So we know that we have a good passcode with a keyword of timezero and just have to figure out how to rearrange the characters to get it!

Substitution: Rotating number of characters, ROT ciphers

You can encrypt a message by "rotating" a certain number of characters. Here, "rotating" means exchanging every letter for one n letters away on the alphabet. For example, recalling Arthur C. Clarke & Stanley Kubric, the letters HAL can be rotated 1 letter to give us IBM. The letter after h is i, and so on. The letter after z is a. This is called a ROT cipher, the most common being ROT13 or Caesar cipher. Decrypting and encrypting are the same, it's just that the total sum of decrypting and encrypting rotations has to equal 26. So ROT1 encrypting can be decrypted with ROT25. That's why ROT13 is popular - it is encrypted and decrypted in the same way. Alternatively, you can encrypt a message by rotating n to the left then decode by rotating n to the right.

Substitution: Variants on ROT ciphers

You can change the n of the substitution with every character. For example, if you have a password, you can use that to encrypt and decrypt a message. This is called Vigenere cipher. I can use the password hello to encrypt a message, this is a message. First, convert hello into the corresponding numbers of the letters that make up the password: h,e,l,l,o is 8,5,12,12,15. Then rotate the message by the corresponding numbers to the right

msg: t  h  i  s    i  s    a    m  e  s  s  a  g  e
ROT: 8  5 12 12   15  8    5   12 12 15  8  5 12 12
out: a  l  t  d    w  z    e    x  p  g  z  e  r  p

so this is a message encrypted with the password hello is altd wz e xpgzerp. To decrypt, rotate each character in the encrypted message to the left by the corresponding number of the password.

Like skip ciphers, there are many variants, and sometimes brute force approaches are necessary.

Substitution: Atbash (mirror) Cipher

Another common substitution method is to flip the order of the alphabet. a becomes z, b becomes y, etc. This is known as the Atbash Cipher

Common encoding techniques

Above we saw that encryption uses ciphers to change the order of characters or substitute one character for another. Below we'll show techniques where you can use different encoding methods to represent a message using different symbols or meanings behind the characters. You can therefore represent a message by changing the encoding of the message. Think of it as changing the character set from standard letters and numbers (a-z A-Z 0-9, or 62 different characters) to something else, or the same characters that mean something else (e.g., in hexadecimal, A means "ten"). There are many, many ways to do this, but here are some common ones:

Morse Code

Morse code is an extremely common way of representing letters and numbers as dots, dashes, and spaces.

ASCII Code

There is a standard way of representing letters in binary so computers can understand them called "ASCII". This represents every character as a number. For more info, see wikipedia or look up ASCII tables. Once you have that number, you can represent that number many different ways: as a binary number, decimal number, octal number, or hexadecimal number. For example a is 91 in decimal, which is 61 in hexadecimal (hex), 141 in octal, and 01100001 in binary. There are plenty of online tools to encode and decode for you. For example, see decodeingress.me's tools.

How do you recognize an ASCII code in a particular base?

  • Decimal: number values ranging from 32 to 126 are "printable" ASCII characters. hello is 104 101 108 108 111
  • Hex: Are two-character sequences consisting of a digit and a letter from A-F. Printable characters have the first digit in the range of 2-7. (i.e, 30 corresponds to the number 0). hello is 68 65 6c 6c 6f
  • Octal: 3 digit numbers consisting of the digits 0-7. Printable characters start at 040 and end at 176. hello is 150 145 154 154 157
  • Binary: Groups of 7 digit or 8 digit sequence of 1s and 0s. If there is an 8 digit sequence, the first digit is a 0. hello is 01101000 01100101 01101100 01101100 01101111

A1Z26 Coding

You can represent every letter in the alphabet with the number of the order of the alphabet. For example, the first letter is a and the 26th is z, so the character a gets the number 1 and z gets the number 26. The word hello is therefore encoded as 8 5 12 12 15. For example, see dcode.fr's tool.

Base64 (and other BaseN) coding

Any string of binary numbers can be represented as "printable" characters using base64 encoding. This is a great trick encoders use to convert almost anything with two symbols (e.g., binary) into readable text. A common use of base64 is to take an ASCII sequence of characters, encode it as a binary sequence of 1s and 0s, and convert that into base64. All of this can easily be handled by many online tools, such as decodeingress.me's tools. Another good tool for decoding different bases (and stringing the output of one to the input of another, among many other things) is CyberChef.

How to recognize base64?

  • Consists of lower and uppercase letters a-z, A-Z, numbers 0-9, plus sign and slash + /, and equal sign =
  • If the last characters are equal signs, it is almost always base64 (or base32, see below).
  • Example: hello is aGVsbG8=

There are many other variants of baseN that encode 1s and 0s (or the ASCII binary 1s and 0s) into other characters. It is good to research and get familiar with those on cyberchef, cryptii, and dcode.fr. What characters are used with which? For example, base32 uses only capital letters A-Z, numbers 2-7, and the equal sign =. For example, see dcode.fr's tool. Additionally, CyberChef magic can be used to guess which base to use if you don't know the exact one.

Steps to decode/decrypt a message

Now that we get the "building blocks" for encoding, we can approach decoding!

  1. Do you have characters in the format you expect? For daily codes in the game Ingress, your final code will be of the format: aaa##keyword###aa, that is 5 digits and the rest letters. So do you have 5 numbers and the rest letters? If so, use the cipher decryption methods above to translate and substitute until you have the solution. You may need a password to use some decryption methods (e.g., Vigenere), which may be hidden somewhere else.
  2. If you don't have the right/expected characters, you can try decoding the message using the coding schemes listed above. Manipulating it should give you something with characters and numbers as expected.
  3. Go to step 1 until there is a solution.

Example

Let's check out IXRuZW1uZXRoZ2lsbkUgZWh0IG5pb0o= from our intro paragraph.

  1. It is unrecognizable text, but it consists only of a-z, A-Z, 0-9, and ends in an equal sign - so maybe it's base64 coding! Use dcode.fr's base64 decoder and see what happens.
  2. Now I have something with punctuation, spaces, lower case letters, and two upper case letters - like a sentence! But the order seems weird - the punctuation is at the front and a capital letter is in the back. This looks like the reverse cipher! Use dcode.fr or another tool to help you reverse it!

Conclusion and Summary

Now you can see the building blocks of solving these puzzles: use combinations of ciphers and coding schemes to manipulate one message to get another. Ciphers change the order of characters or substitute one character for another, coding schemes change the representation of one set of characters or symbols into another set of characters or symbols. There are many, many ways of doing it, this just presented a few common ones to get the reader started, so now it's good to explore and learn as many as you can - both what they do and how they work!

Next step?

Want to try more puzzles? Check out ingress.codes for a collection of previous puzzles with solution walkthroughs.