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ISC2 CC 5.1 CompTIA Security+ 1.4 Cisco CCST Cybersecurity 1.4
TechKnowSurge Catalog Interactives Key Space Calculator
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Key Space Calculator

Type the answers: shift letters with a key, count how many keys a bit length allows, and size a one-time pad.

⚑ Complete this interactive to capture a CTF flag worth 5 points.

About this interactive

A cipher needs three things: the message, the algorithm, and a key. This activity practises the key, the way the lesson did. First, shifting. A key of 3 moves every letter three places along the alphabet, so A becomes D and CAB becomes FDE. To decrypt, shift back by the same amount. When a shift runs past Z it wraps around to A, so with a key of 8, S becomes A and T becomes B. A longer key such as 8, 2 alternates between two shifts, which is why the two E letters in SECRET come out as different letters and the easy "most common letter" trick stops working. Second, bits. Computer keys are measured in bits, and each bit can be 0 or 1. One bit gives 2 possible keys, two bits give 4, three bits give 8. The rule is 2 to the power of the number of bits: 8 bits is 256 possible keys, 10 bits is 1,024. Every bit you add doubles the number of keys an attacker would have to try. That is why DES, whose key is 64 bits long but only 56 of them count, could eventually be cracked, and why AES starts at 128 bits. Third, the one-time pad, the one cipher that is theoretically uncrackable. Its key must be at least as long as the message, completely random, kept completely secret, and never used again. Break any one of those rules and the guarantee is gone.

What you'll learn

Aligned to

ISC2 CC
5.1 Understand data security
CompTIA Security+
1.4 Explain the importance of using appropriate cryptographic solutions.
Cisco CCST Cybersecurity
1.4 Explain encryption methods and applications

Key terms

Key
Additional information used in combination with a cipher to encode or decode a secret message.
Key Length
The size of a cryptographic key measured in bits, where each additional bit doubles the number of possible key combinations and increases encryption strength.
One-Time Pad
A theoretically uncrackable encryption method that uses a random key at least as long as the plaintext, used only once and kept completely secret.
Plaintext
The original, readable message before it has been converted into a hidden or encrypted format.
Ciphertext
The scrambled, unreadable output produced after plaintext has been encrypted using a cipher.
Digital Encryption Standard
DES
Digital Encryption Standard is a symmetric-key block cipher with a 56-bit key that was once the federal standard for encryption but is now considered cryptographically broken due to its small key size.
Advanced Encryption Standard
AES
A symmetric encryption algorithm widely used to secure data, supporting key sizes of 128, 192, and 256 bits.

Topics

Interactive Calculation

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