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Eccouncil 212-81 Exam Questions
- Topic 1: Information Theory Cryptography Concepts/ Multi-Alphabet Substitution
- Topic 2: Introduction and History of Cryptography/ Breaking the Vigenère Cipher
- Topic 3: Symmetric Cryptography & Hashes/ Single Substitution Weaknesses
- Topic 4: Symmetric Block Cipher Algorithms/ Basic Facts of the Feistel Function
- Topic 5: International Data Encryption Algorithm (IDEA)/ History of Cryptography
- Topic 6: Number Theory and Asymmetric Cryptography/ Advanced Encryption Standard (AES)
- Topic 7: Propagating Cipher-Block Chaining (PCBC)/ Naor-Reingold and Mersenne Twister Pseudorandom Function
- Topic 8: Server-based Certificate Validation Protocol/ Classification of Random Number Generator
- Topic 9: Shiva Password Authentication Protocol (S-PAP)/ Challenge-Handshake Authentication Protocol (CHAP)
- Topic 10: Point-to-Point Tunneling Protocol (PPTP)/ National Security Agency and Cryptography
- Topic 11: Cracking Modern Cryptography: Ciphertext-only and Related-key Attack/ Cracking Modern Cryptography: Chosen Plaintext Attack
- Topic 12: Steganography Implementations/ Example of Symmetric Stream Ciphers: RC4
- Topic 13: Birthday Paradox: Probability/ Mono-Alphabet Substitution
- Topic 14: Cracking Modern Cryptography/ Example of Symmetric Stream Ciphers: PIKE
Free Eccouncil 212-81 Exam Actual Questions
Note: Premium Questions for 212-81 were last updated On Jul. 07, 2026 (see below)
A part of understanding symmetric cryptography understands the modes in which it can be used. You are
explaining those modes to a group of cryptography students. The most basic encryption mode is____________.
The message is divided into blocks, and each block is encrypted separately with no modification to the process.
John is trying to explain the basics of cryptography to a group of young, novice, security students. Which one of the following most accurately defines encryption?
Changing a message so it can only be easily read by the intended recipient
https://en.wikipedia.org/wiki/Encryption
Encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.
The reverse process from encoding - converting the encoded message back into its plaintext format.
Decoding
Decoding - reverse process from encoding,converting the encoded message back into its plaintext format.
The mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext.
Output feedback (OFB)
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_(OFB)
The output feedback (OFB) mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext. Just as with other stream ciphers, flipping a bit in the ciphertext produces a flipped bit in the plaintext at the same location. This property allows many error-correcting codes to function normally even when applied before encryption.
Incorrect answers:
Cipher feedback (CFB)- mode, a close relative of CBC, makes a block cipher into a self-synchronizing stream cipher.
Electronic codebook (ECB)- the simplest of the encryption modes (named after conventional physical codebooks). The message is divided into blocks, and each block is encrypted separately.
Cipher-block chaining (CBC)- Ehrsam, Meyer, Smith and Tuchman invented the cipher block chaining (CBC) mode of operation in 1976. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This way, each ciphertext block depends on all plaintext blocks processed up to that point. To make each message unique, an initialization vector must be used in the first block.
What is the largest key size that AES can use?
256
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits.
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