KRYPTOG Logs

ECB and CTR allow parallel encryption; all modes except ECB need an IV; ECB and CBC need padding while OFB and CTR don't. Property ECB CBC OFB CTR IV needed No Yes Yes Yes Parallel encryption Yes No No Yes Parallel decryption Yes Yes No Yes Padding needed Yes Yes No...

Quiz: KRYPTOG / Symmetric Cryptography | updated: Jul 14, 2026

Stream ciphers encrypt bit by bit with a keystream (fast, no padding, no integrity), while block ciphers encrypt fixed-size blocks (more versatile, can provide integrity via MAC). Property Stream Cipher Block Cipher Unit of encryption Bit/byte Fixed-size block (e.g., 128 b...

Quiz: KRYPTOG / Symmetric Cryptography | updated: Jul 14, 2026

AES-128 uses a 128-bit key, which is 16 bytes. Quick conversion: 128 bits ÷ 8 bits/byte = 16 bytes. All AES variants: Variant Key bits Key bytes Block bits Block bytes AES-128 128 16 128 16 AES-192 192 24 128 16 AES-256 256 32 128 16 Note: The block size is always 1...

Quiz: KRYPTOG / Symmetric Cryptography | updated: Jul 14, 2026

False — steganography hides the existence of a message, while encryption hides its content. They are fundamentally different techniques. Technique Hides... Example Encryption The content of the message AES-encrypted file (obviously encrypted, but unreadable) Steganograph...

Quiz: KRYPTOG / Introduction to Cryptology | updated: Jul 14, 2026

Exactly $\log_2(n)$ bits are needed to distinguish between $n$ equally likely characters. $$\text{bits} = \log_2(n)$$ $n$ (characters) Bits needed 2 1 4 2 8 3 16 4 26 (alphabet) 4.7 256 (byte) 8 This follows directly from the entropy formula: when all characte...

Quiz: KRYPTOG / Fundamentals of Cryptography | updated: Jul 14, 2026

Symmetric needs 499,500 keys; asymmetric needs only 1000 key pairs. Symmetric: $$\frac{n(n-1)}{2} = \frac{1000 \times 999}{2} = 499{,}500 \text{ keys}$$ Asymmetric: $$n = 1{,}000 \text{ key pairs}$$ The scaling problem visualized: Participants Symmetric Keys Asymmetric Key Pai...

Quiz: KRYPTOG / Fundamentals of Cryptography | updated: Jul 14, 2026

DES uses a 56-bit key with 64-bit blocks over 16 Feistel rounds — it's insecure because 2^56 keys can be brute-forced in hours with modern hardware. DES parameters: Parameter Value Block size 64 bits Key length 56 bits (64 bits input, 8 are parity) Rounds 16 Structur...

Quiz: KRYPTOG / Symmetric Cryptography | updated: Jul 14, 2026

The classic approach is: compute the MAC (or signature) over the plaintext first, then encrypt everything — known as MAC-then-Encrypt or "authenticate then encrypt." * The MAC covers the plaintext; the body is then encrypted, with the tag carried in the trailer. * Message struct...

Quiz: KRYPTOG / One-Way and Hash Functions | updated: Jul 14, 2026

Convert 13 to binary: $(1101)_2$. Start with P, then for each remaining bit left-to-right: always DOUBLE, and additionally ADD P for each "1" bit. Trace: $P \to 3P \to 6P \to 13P$ (the bits after the leading 1 are 1, 0, 1 → double-add, double, double-add). * Scanning the bits of...

Quiz: KRYPTOG / Elliptic Curve Cryptography | updated: Jul 14, 2026

SAM computes $a^m \mod N$ by converting the exponent to binary, then processing each bit: square for every bit, additionally multiply for each "1" bit — reducing mod N at every step. * Square-and-Multiply computing 5²² mod 11: walk the exponent's bits (10110) left to right, squa...

Quiz: KRYPTOG / Mathematics for Asymmetric Cryptography | updated: Jul 14, 2026