Which Photo Has the Secret?

About this interactive

Here are two photos of the same sunset. One is the original. The other has a secret message hidden inside it. Which is which? Look as long as you like, zoom right into the corner, and then commit to a guess — because the honest answer is that nobody can tell, and that is the whole idea behind steganography. Cryptography turns a message into code: anyone who intercepts it can see a secret is there, even if they cannot read it, and may start trying to break it. Steganography hides the message inside something ordinary, like a photo or an audio file, so nobody thinks to look. After your guess, the activity zooms in on the pixels. Every color is stored as three 8-bit numbers for red, green and blue, and the message lives only in the rightmost bit of each one, the least significant bit. A value of 200 becomes 201; the color does not visibly change. Read those last bits in groups of eight and the message falls out — which is also steganography’s weakness, and why encrypting a message before hiding it is the stronger move. Then you hide a word of your own and watch every bit land in the photo, before five quick questions check what stuck.

How to play

Four short steps:

Guess — one of two photos hides a secret message. Study them, zoom in if you like, then lock in a guess. The guess is not scored.
Look closer — see which photo it was, compare the same pixels as numbers and binary, and read the hidden message back out.
Hide one — type a short word (up to 6 characters) and watch each of its bits written into the photo’s color values.
Check — answer five quick questions. Some are multiple choice; some ask you to type a number.

Your score is the number of questions you get right out of 5; 4 of 5 (80%) passes. Reset gives you a fresh photo and a new set of questions.

What you'll learn

Explain why steganography hides the fact that a secret exists while cryptography hides what the secret says
Describe how writing message bits into the least significant bit of each color value hides a message in an image without a visible change
Explain why encrypting a message before embedding it in a carrier file protects it even if the hidden data is found

Aligned to

CompTIA Security+

1.4 Explain the importance of using appropriate cryptographic solutions.

NIST NICE

K0884 Knowledge of covert communication tools and techniques

K0942 Knowledge of cryptology principles and practices

S0652 Skill in performing bit-level analysis

Cisco CCST Cybersecurity

1.4 Explain encryption methods and applications

CompTIA Tech+

6.6 Explain common uses of encryption

Key terms

Steganography: The practice of concealing a message within another medium, such as an image or sentence, so its existence is hidden rather than its content scrambled.
Least Significant Bit: The lowest-value bit in a binary number, located at the far right, whose modification causes the smallest possible change to the overall value and is used in steganography to embed hidden data with minimal perceptible alteration.
Cryptography: The practice of securing information by transforming it into an unreadable format using mathematical algorithms.
Encryption: The process of converting readable data into an unreadable format using an algorithm and key to prevent unauthorized access.

Topics

Interactive Steganography Cryptography Confidentiality Binary Pixel

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