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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 May. 25, 2026 (see below)
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.
Used to take the burden off of a CA by handling verification prior to certificates being issued. Acts as a proxy between user and C
RA (Registration Authority)
https://en.wikipedia.org/wiki/Registration_authority
Registration authorities exist for many standards organizations, such as ANNA (Association of National Numbering Agencies for ISIN), the Object Management Group, W3C, IEEE and others. In general, registration authorities all perform a similar function, in promoting the use of a particular standard through facilitating its use. This may be by applying the standard, where appropriate, or by verifying that a particular application satisfies the standard's tenants. Maintenance agencies, in contrast, may change an element in a standard based on set rules -- such as the creation or change of a currency code when a currency is created or revalued (i.e. TRL to TRY for Turkish lira). The Object Management Group has an additional concept of certified provider, which is deemed an entity permitted to perform some functions on behalf of the registration authority, under specific processes and procedures documented within the standard for such a role.
Incorrect answers:
TTP (Trusted Third Party) - is an entity which facilitates interactions between two parties who both trust the third party; the Third Party reviews all critical transaction communications between the parties, based on the ease of creating fraudulent digital content. In TTP models, the relying parties use this trust to secure their own interactions. TTPs are common in any number of commercial transactions and in cryptographic digital transactions as well as cryptographic protocols, for example, a certificate authority (CA) would issue a digital identity certificate to one of the two parties in the next example. The CA then becomes the Trusted-Third-Party to that certificates issuance. Likewise transactions that need a third party recordation would also need a third-party repository service of some kind or another.
CP (Certificate Policy) - is a document which aims to state what are the different entities of a public key infrastructure (PKI), their roles and their duties. This document is published in the PKI perimeter.
When in use with X.509 certificates, a specific field can be set to include a link to the associated certificate policy. Thus, during an exchange, any relying party has an access to the assurance level associated with the certificate, and can decide on the level of trust to put in the certificate.
PKI (Public Key Infrastructure) - is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facilitate the secure electronic transfer of information for a range of network activities such as e-commerce, internet banking and confidential email. It is required for activities where simple passwords are an inadequate authentication method and more rigorous proof is required to confirm the identity of the parties involved in the communication and to validate the information being transferred.
Jane is looking for an algorithm to ensure message integrity. Which of following would be an acceptable choice?
Integrity. In information security, data integrity means maintaining and assuring the accuracy and completeness of data over its entire lifecycle. This means that data cannot be modified in an unauthorized or undetected manner.
An important application of hashes is verification of message integrity. Comparing message digests (hash digests over the message) calculated before, and after, transmission can determine whether any changes have been made to the message or file.
SHA-1
https://en.wikipedia.org/wiki/SHA-1
SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest -- typically rendered as a hexadecimal number, 40 digits long. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard.
Incorrect answers:
RSA (Rivest--Shamir--Adleman) is one of the first public-key cryptosystems and is widely used for secure data transmission.
RC4 (Rivest Cipher 4 also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is a stream cipher.
AES (Advanced Encryption Standard) is a subset of the Rijndael block cipher
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