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Quizzes > Computers & Technology > Programming & Software

Take the Ultimate Cryptography Quiz and Prove Your Skills

Ready for the cryptography test? Dive into digital signatures, DES & more!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art padlock key code symbols on teal background for cryptography quiz on digital signatures DES symmetric key

Think you're a crypto pro? Step right up to our cryptography quiz, designed to challenge aspiring cybersecurity specialists and curious codebreakers. You'll tackle cryptography questions spanning hands-on DES quiz scenarios to advanced symmetric-key cryptography quiz problems - while exploring the fundamentals of secure digital communication. This cryptography test goes beyond definitions to reveal the art of crafting and validating digital signatures, putting your critical thinking to the trial. Perfect for developers, security students, or anyone intrigued by encryption, this digital signatures quiz will sharpen your skills and boost your confidence. Ready to prove your expertise? Jump in now and don't miss our algorithm quiz for more brain-teasing fun!

What does DES stand for?
Data Encryption Standard
Digital Encryption Software
Data Encapsulation Scheme
Designated Encryption System
DES stands for Data Encryption Standard, which was developed by IBM and adopted by NIST in 1977 as a federal encryption standard. It uses a 56-bit key and operates on 64-bit blocks. Despite its historical significance, its short key length is no longer considered secure against modern brute-force attacks. FIPS 46-3: Data Encryption Standard
Which algorithm uses a Feistel structure?
DES
AES
RSA
ECC
DES is built on the classic Feistel network structure, which splits the block into halves and applies rounds of substitution and permutation. AES uses a substitution–permutation network instead. Feistel ciphers enable encryption and decryption operations to be very similar. Feistel Cipher - Wikipedia
What is symmetric-key cryptography?
Encryption and decryption using the same secret key
Use of one public key and one private key
Hashing without a key
Encryption based on biometric data
Symmetric-key cryptography involves the same secret key for both encryption and decryption. It is generally faster than asymmetric methods but requires secure key distribution. Common algorithms include DES, AES, and Blowfish. Symmetric-key Algorithm - Wikipedia
What is the effective key length of DES?
56 bits
64 bits
128 bits
40 bits
DES uses a 64-bit key input, but only 56 bits are actually used for encryption; the other 8 bits are used for parity. This 56-bit effective key length has been shown to be vulnerable to brute-force attacks. Modern standards recommend using longer key lengths like those in AES. FIPS 46-3: Data Encryption Standard
Which of these is a block cipher?
AES
RC4
SHA-1
RSA
AES (Advanced Encryption Standard) is a symmetric block cipher that operates on 128-bit blocks. RC4 is a stream cipher, SHA-1 is a hash function, and RSA is an asymmetric algorithm. AES is widely used in protocols like TLS and SSH. FIPS 197: Advanced Encryption Standard
True or False: In symmetric encryption, the sender and receiver share the same key.
True
False
Symmetric encryption requires both the sender and the receiver to share a single secret key for both encryption and decryption. This key must be kept confidential and distributed securely in advance. The shared-key model contrasts with asymmetric encryption, which uses key pairs. Symmetric-key Algorithm - Wikipedia
What is diffusion in cryptography?
Spreading the influence of one plaintext bit over many ciphertext bits
Mixing the key bits thoroughly
Ensuring decryption only with the correct key
Generating random numbers for encryption
Diffusion is a property that ensures that changing one bit of the plaintext results in many bits of ciphertext changing. It helps hide statistical structure in the plaintext. Claude Shannon introduced the concept along with confusion. Diffusion (Cryptography) - Wikipedia
Which of the following is NOT a property of a cryptographic hash function?
Reversibility
Collision resistance
Preimage resistance
Deterministic output
Cryptographic hash functions are one-way and thus not reversible. They provide collision resistance and preimage resistance, meaning it's infeasible to find two inputs with the same hash or to recover the input from the hash. They are also deterministic in that the same input always produces the same output. Cryptographic Hash Function - Wikipedia
What does IV stand for in block cipher modes?
Initialization Vector
Input Value
Indexed Variable
Internal Vector
IV stands for Initialization Vector, a non-secret random or pseudorandom value used to ensure distinct ciphertexts for identical plaintexts under the same key. It is required in modes like CBC and CFB. The IV must be unpredictable but does not need to be kept secret. Initialization Vector - Wikipedia
Which one is an example of a stream cipher?
RC4
AES
DES
SHA-256
RC4 is a symmetric stream cipher that generates a pseudorandom keystream which is XORed with plaintext. AES and DES are block ciphers, and SHA-256 is a hash function. Stream ciphers encrypt data one bit or byte at a time. RC4 - Wikipedia
Which mode of operation uses ciphertext feedback and an IV?
CFB
ECB
CTR
GCM
Cipher Feedback (CFB) mode uses an IV and feedback of the previous ciphertext block to encrypt the next plaintext block. ECB does not use an IV or feedback, CTR uses counters, and GCM adds authentication on top of CTR. CFB can operate in smaller segments than the block size. CFB Mode - Wikipedia
What is plaintext?
Original readable message before encryption
Encrypted message after cipher
Hash output
Digital signature
Plaintext is the original, unencrypted data that is input into a cryptographic algorithm. After encryption, plaintext becomes ciphertext. Maintaining the confidentiality of plaintext is the primary goal of encryption. Plaintext - Wikipedia
What is ciphertext?
Encrypted output after encryption
Original message before encryption
Hash of the message
Private key
Ciphertext is the result of encryption performed on plaintext using an algorithm and key. It appears random and is unreadable without the proper decryption key. Converting ciphertext back to plaintext is done via decryption. Ciphertext - Wikipedia
True or False: A digital signature provides non-repudiation.
True
False
Digital signatures provide non-repudiation by binding a signer to the signed data with their private key. Once verified with the public key, the signer cannot credibly deny their signature. This ensures integrity, authenticity, and non-repudiation. Digital Signature - Wikipedia
Which key is public in asymmetric cryptography?
Public key
Private key
Session key
Symmetric key
In asymmetric cryptography, the public key is distributed openly while the private key is kept secret. The public key encrypts data or verifies signatures, and the private key decrypts data or creates signatures. This key pair model enables secure key exchange and digital signatures. Public-key Cryptography - Wikipedia
What is triple DES?
Encrypt-Decrypt-Encrypt with DES using two or three keys
Applying DES three times in ECB only
AES run three rounds
Combining DES with RSA
Triple DES applies the DES cipher three times: encrypt, decrypt, then encrypt again, using either two or three keys. This extends DES’s key length to 112 or 168 bits. It was designed to increase security while remaining compatible with legacy DES. Triple DES - Wikipedia
Which describes the main weakness of ECB mode?
Identical plaintext blocks produce identical ciphertext blocks
It requires an IV for every block
It cannot be parallelized
It leaks the key through padding
Electronic Codebook (ECB) mode encrypts each block independently, so identical plaintext blocks map to identical ciphertext blocks. This pattern leakage makes ECB unsuitable for most applications. Other modes like CBC or GCM avoid this by using chaining or randomization. ECB Mode - Wikipedia
How many rounds does the standard DES algorithm use?
16
8
12
64
DES performs 16 rounds of its Feistel network, each involving expansion, substitution via S-boxes, permutation, and key mixing. This round count contributes to its security of the era. Modern ciphers like AES use more complex structures and different round counts. DES - Wikipedia
RSA digital signatures rely primarily on which mathematical operation?
Modular exponentiation with a private key
Bitwise XOR operations
Elliptic curve addition
Matrix multiplication
RSA signatures are created by raising the hash of the message to the private exponent modulo the RSA modulus. Verification uses the corresponding public exponent. The security relies on the difficulty of factoring large integers. RSA (cryptosystem) - Wikipedia
Which algorithm was selected by NIST as the successor to DES?
AES
3DES
Blowfish
RC4
After a multi-year competition, NIST selected Rijndael as the Advanced Encryption Standard (AES) in 2001. AES supports 128-bit blocks and key sizes of 128, 192, or 256 bits. It replaced both DES and 3DES for U.S. government applications. FIPS 197: AES
What is the avalanche effect in cryptography?
A small change in input leads to a significant change in output
Key exhaustion under repeated use
Loss of nonlinear properties
Performance degradation with large blocks
The avalanche effect describes how a minor change in plaintext or key (like flipping one bit) produces a large, unpredictable change in ciphertext. This property is important for resisting statistical attacks. Good ciphers exhibit strong avalanche behavior. Avalanche Effect - Wikipedia
In HMAC, which components are combined?
A cryptographic hash function and a secret key
Two hash functions
A private and public key
A cipher and a hash
HMAC combines a cryptographic hash function with a secret key to produce a message authentication code. It provides integrity and authenticity. HMAC is standardized in RFC 2104 and widely used in protocols like TLS and IPSec. RFC 2104: HMAC
Which block cipher mode provides confidentiality only, without built-in integrity?
CBC
GCM
HMAC
GHASH
Cipher Block Chaining (CBC) provides confidentiality by chaining blocks with XOR operations but offers no integrity check. GCM (Galois/Counter Mode) adds authentication. HMAC and GHASH are MAC mechanisms, not standalone block cipher modes. CBC Mode - Wikipedia
What is the primary purpose of a Public Key Infrastructure (PKI)?
Managing digital certificates and public keys
Encrypting email automatically
Distributing symmetric keys
Generating random numbers
PKI is a framework for creating, distributing, managing, and revoking digital certificates and public keys. It enables trust in parties’ identities and secure communications. Certificate Authorities (CAs) are central to PKI operations. Public Key Infrastructure - Wikipedia
Which of these hash functions is considered collision-resistant?
SHA-256
MD5
CRC32
SHA-0
SHA-256 is part of the SHA-2 family and remains collision-resistant under current knowledge. MD5 and SHA-0 have known collisions, and CRC32 is designed for error-checking, not cryptographic security. SHA-256 is widely used for secure hashing. SHA-2 - Wikipedia
What is the block size of AES?
128 bits
64 bits
256 bits
32 bits
AES operates on 128-bit blocks irrespective of key size. It supports key lengths of 128, 192, or 256 bits. The fixed block size simplifies implementation and analysis. FIPS 197: AES
Which protocol is commonly used for key exchange in symmetric systems?
Diffie-Hellman
RSA signature
SHA-1
AES-GCM
Diffie-Hellman key exchange allows two parties to agree on a shared secret over an insecure channel without prior shared secrets. It relies on the discrete logarithm problem. The shared secret can then be used for symmetric encryption. Diffie–Hellman Key Exchange - Wikipedia
What type of attack involves having pairs of plaintext and corresponding ciphertext?
Known-plaintext attack
Chosen-ciphertext attack
Brute-force attack
Side-channel attack
In a known-plaintext attack, the attacker has access to both plaintext and corresponding ciphertext and uses this information to deduce the key or algorithm properties. It is more powerful than ciphertext-only attacks but less so than chosen-plaintext attacks. Many ciphers are designed to resist this attack. Known-Plaintext Attack - Wikipedia
Which algorithm is widely used for digital signatures?
RSA
AES
DES
MD5
RSA is commonly used for digital signatures because it allows one to sign hashes of messages with a private key and verify them with the public key. It is based on the difficulty of factoring large integers. Other signature algorithms include DSA and ECDSA. RSA (cryptosystem) - Wikipedia
What is key stretching?
A technique to make a weak key more secure by increasing computational work
Reducing a key size to fit hardware constraints
Compressing keys using hash functions
Encrypting a key with itself
Key stretching uses algorithms like PBKDF2, bcrypt, or scrypt to repeatedly process a weak key or password, increasing the computational effort required for each guess. This helps defend against brute-force and dictionary attacks. It is commonly used in password-based key derivation. Key Stretching - Wikipedia
How does CBC mode chaining work?
Each plaintext block is XORed with the previous ciphertext block before encryption
Plaintext blocks are encrypted independently
Ciphertext blocks are XORed with the next plaintext block
Blocks are hashed before encryption
In Cipher Block Chaining (CBC) mode, each plaintext block is XORed with the previous ciphertext block (or IV for the first block) before being encrypted. This creates interdependence between blocks and conceals patterns in the plaintext. CBC requires proper IV handling for security. CBC Mode - Wikipedia
Why is ECB mode generally discouraged?
It reveals patterns by encrypting identical plaintext blocks to identical ciphertext
It is slower than other modes
It requires complex key schedules
It cannot be implemented in hardware
ECB mode encrypts each block independently, so repeating plaintext blocks yield identical ciphertext blocks, leaking structure. This makes it insecure for most applications where data patterns matter. Safer modes like CBC or GCM use chaining or counters to randomize encryption. ECB Mode - Wikipedia
What is the primary difference between a MAC and a digital signature?
A MAC uses a shared secret key, while a digital signature uses an asymmetric key pair
A MAC uses asymmetric keys, while a signature uses a shared secret
A MAC provides non-repudiation, a signature does not
A MAC is slower than digital signatures
A Message Authentication Code (MAC) uses a shared symmetric key for both generation and verification, providing integrity and authenticity but not non-repudiation. A digital signature uses a private key to sign and a public key to verify, enabling non-repudiation. Each has distinct use cases in security protocols. MAC - Wikipedia
What impact does the birthday paradox have on hash functions?
It shows collisions can be found in roughly 2^(n/2) operations for an n-bit hash
It doubles the security of the hash function
It halves the hash output length
It makes hash functions irreversible
The birthday paradox implies that for an n-bit hash, collisions can be expected after about 2^(n/2) hashing operations, rather than 2^n. This reduces the effective collision resistance. Designers choose sufficiently large digest sizes (e.g., 256 bits) to mitigate this. Birthday Attack - Wikipedia
What is differential cryptanalysis?
An attack analyzing differences in plaintext pairs to find key bits
A side-channel timing attack
A social engineering method
A method of key exchange
Differential cryptanalysis studies how differences in plaintext pairs affect differences at the output after encryption. By collecting statistics on these differences over many encryptions, attackers can deduce key bits. It is a powerful chosen-plaintext attack on block ciphers. Differential Cryptanalysis - Wikipedia
Poly1305 is which type of cryptographic primitive?
Message Authentication Code (MAC)
Block cipher
Public key algorithm
Secure hash function
Poly1305 is a one-time universal hash function used for message authentication, providing a MAC. It is used in conjunction with a cipher like ChaCha20 in the AEAD construction ChaCha20-Poly1305. Poly1305 ensures data integrity and authenticity. Poly1305 - Wikipedia
What is an S-box in block cipher design?
A substitution box that performs nonlinear mapping
A key scheduling algorithm
A mode of operation
A hash function component
An S-box (substitution box) provides nonlinear transformation of input bits to output bits, crucial for the cipher’s security. It thwarts linear and differential cryptanalysis by introducing confusion. Block ciphers like DES and AES use S-boxes. S-box - Wikipedia
Why is padding needed in block cipher encryption?
To fill the last block when plaintext length isn't a multiple of block size
To increase key entropy
To randomize the IV
To sign the message
Block ciphers require inputs that match their fixed block size. Padding schemes like PKCS#7 fill the remaining bytes of the final block to the required length. Proper padding and removal ensure data integrity and prevent padding oracle attacks. Padding (Cryptography) - Wikipedia
What is a Certificate Revocation List (CRL)?
A list of digital certificates that have been revoked before their expiration date
A database of public keys for PKI
A list of symmetric keys to be rotated
A log of all issued certificates
A CRL is published by a Certificate Authority to list certificates that are no longer trusted before their scheduled expiration. Clients check the CRL to ensure a certificate has not been revoked. It is part of PKI’s certificate lifecycle management. CRL - Wikipedia
What is forward secrecy?
A property where session keys cannot be compromised even if long-term keys are compromised
Rekeying symmetric keys every hour
Using only public keys for encryption
Encrypting data with forward chaining
Forward secrecy ensures that compromise of long-term private keys does not compromise past session keys. Protocols like Diffie-Hellman Ephemeral (DHE) provide this property by generating unique ephemeral keys. It protects past communications even if current keys are exposed. Forward Secrecy - Wikipedia
How does the Diffie-Hellman key exchange ensure secrecy of the shared key?
By relying on the hardness of the discrete logarithm problem
By using symmetric encryption internally
By hashing the exchanged values
By using pre-shared keys
Diffie-Hellman key exchange relies on the discrete logarithm problem’s computational difficulty. Parties exchange public values derived from private exponents, without revealing them. The shared secret is computed locally and never transmitted. Diffie–Hellman Key Exchange - Wikipedia
What is a key schedule in DES?
An algorithm to derive sixteen round keys from the main key
A timetable for key rotation
A block cipher mode
A type of padding
The key schedule in DES takes the 56-bit main key and generates sixteen 48-bit subkeys for each encryption round. It involves permutations and left rotations. The schedule ensures that each round uses a different subkey, adding complexity. DES Key Schedule - Wikipedia
What is a side-channel attack?
An attack exploiting physical implementation characteristics like timing or power consumption
A brute-force attack on the key
Using chosen plaintext only
Intercepting encrypted traffic only
Side-channel attacks gather information from the physical implementation of a cryptosystem, such as timing, power usage, or electromagnetic leaks. Such leaks can reveal secret keys even if the algorithm is mathematically secure. Countermeasures include constant-time implementations and shielding. Side-channel Attack - Wikipedia
What is salting in password hashing?
Adding random data to each password before hashing to prevent precomputed attacks
Hashing the password multiple times
Using a secret key for hashing
Encrypting the hash with a symmetric key
A salt is random data appended or prepended to a password before hashing to ensure that identical passwords hash to different values. This thwarts rainbow table and precomputed dictionary attacks. Each user should have a unique salt. Salt (Cryptography) - Wikipedia
What is a Key Derivation Function (KDF)?
A function that derives strong cryptographic keys from a secret value like a password
A mode of block cipher operation
A public key generation algorithm
A hash function with no key
A Key Derivation Function (KDF) takes a secret input (e.g., a password) and generates one or more cryptographic keys. It often includes salting and multiple iterations to resist brute-force attacks. Examples include PBKDF2, bcrypt, and scrypt. Key Derivation Function - Wikipedia
What is a meet-in-the-middle attack on Double DES?
An attack using two-phase encryption and decryption to reduce complexity from 2^112 to about 2^57
A brute-force approach on single DES
An algebraic attack on the key schedule
A side-channel method
The meet-in-the-middle attack on Double DES exploits the fact that Double DES uses two sequential DES operations. By encrypting plaintext under all possible first keys and decrypting ciphertext under all possible second keys, an attacker finds a match in roughly 2^57 operations. This breaks the expected 112-bit security. Meet-in-the-Middle Attack - Wikipedia
What defines a chosen-ciphertext attack (CCA)?
An attacker can decrypt arbitrary chosen ciphertexts and use results to compromise the system
An attacker only sees ciphertext
An attacker chooses plaintexts to encrypt
An attacker exploits side channels
In a chosen-ciphertext attack, the adversary can submit ciphertexts of their choice to a decryption oracle and obtain plaintexts. Adaptive CCAs allow multiple queries, making CCA resistance critical for secure public-key encryption. Schemes like RSA-OAEP aim to resist CCA. Chosen-Ciphertext Attack - Wikipedia
How does the RSA-PSS signature scheme enhance security over basic RSA signatures?
It uses probabilistic salt and a provably secure padding method
It uses shorter keys for performance
It eliminates hashing of the message
It replaces exponentiation with elliptic curves
RSA-PSS (Probabilistic Signature Scheme) adds random salt to the message hash and uses a carefully designed padding scheme. This probabilistic padding provides provable security against adaptive attacks in the random oracle model. It is recommended in PKCS#1 v2.1. RSA-PSS - Wikipedia
What is format-preserving encryption (FPE)?
Encryption that preserves the format and length of the plaintext
A strong hash function for fixed-length data
A block cipher mode that uses stream cipher
RSA with fixed padding
Format-Preserving Encryption (FPE) encrypts data while ensuring the ciphertext has the same format (e.g., length, character set) as the plaintext. It is useful for encrypting credit card numbers or social security numbers without altering database schemas. Standards include NIST SP 800-38G. NIST SP 800-38G
What advantage does lattice-based cryptography offer?
Resistance to quantum computer attacks
Smaller key sizes than AES
No need for randomness
Built-in message authentication
Lattice-based cryptography relies on hard problems in high-dimensional lattices, which are believed to resist attacks by quantum computers (unlike RSA and ECC). Schemes like Learning With Errors (LWE) underpin many post-quantum proposals. They provide strong security guarantees. Lattice-based Cryptography - Wikipedia
How does quantum computing threaten RSA security?
Shor's algorithm can factor large integers in polynomial time
Grover's algorithm breaks RSA signatures directly
Quantum annealing breaks symmetric ciphers
Quantum entanglement can decrypt any message
Shor's algorithm enables a quantum computer to factor large integers efficiently, breaking RSA’s security assumption. If large-scale quantum computers become practical, RSA and other factorization-based schemes will be insecure. This motivates post-quantum cryptography research. Shor's Algorithm - Wikipedia
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Study Outcomes

  1. Understand symmetric-key cryptography basics -

    Explore how symmetric algorithms rely on shared secrets for encryption and decryption, including key management considerations.

  2. Analyze DES strengths and weaknesses -

    Examine the Data Encryption Standard's algorithm structure, key length implications, and common cryptanalytic attacks.

  3. Differentiate digital signature mechanisms -

    Compare how digital signatures ensure authentication, integrity, and non-repudiation using asymmetric key pairs.

  4. Apply cryptographic best practices -

    Learn when to choose appropriate protocols and implement secure key generation and distribution techniques.

  5. Identify knowledge gaps in cryptography -

    Use quiz feedback to pinpoint areas for improvement in your understanding of cryptographic concepts and techniques.

Cheat Sheet

  1. Symmetric-Key Cryptography Essentials -

    Single shared secret key for encryption/decryption makes symmetric-key cryptography lightning-fast and is central to many symmetric-key cryptography quiz questions. The mathematical operation C = E(K, P) shows how plaintext P transforms with key K to ciphertext C. Mnemonic: "Same key, same secret" helps lock in the concept (NIST SP 800-57).

  2. Data Encryption Standard (DES) Structure -

    DES operates as a 16-round Feistel network with a 56-bit key and initial/final permutations, a favorite topic on the DES quiz. Each round uses expansion, key mixing, substitution (via S-boxes), and permutation - e.g., a 6-bit input to an S-box yields a 4-bit output. Remember the vulnerability: 2^56 brute force is now trivial (FIPS 46-3).

  3. Digital Signatures Workflow -

    Digital signatures quiz questions often test RSA-based signing: sign S = H(m)^d mod n and verify by checking S^e mod n = H(m) from a collision-resistant hash H. This dual process ensures authenticity and non-repudiation - think "Hash, Exponentiate, Authenticate" as a mnemonic. Reference: RFC 8017 outlines the full scheme.

  4. Block Cipher Modes Overview -

    Cryptography quiz questions on modes will contrast ECB (stateless), CBC (uses IV and chaining), and CTR (turns block cipher into a stream cipher with a counter). For example, CBC: C_i = E(K, P_i XOR C_{i-1}), with C_0 = IV, ensures identical plaintext blocks encrypt differently. NIST SP 800-38A is your go-to source, and remembering "Chain Blocks Carefully" locks it in.

  5. Key Management & Distribution Protocols -

    Secure communication hinges on robust key distribution - expect Kerberos or Diffie-Hellman questions on your cryptography test. Kerberos uses a Ticket Granting Ticket to share session keys confidentially via a trusted Key Distribution Center (MIT Kerberos project). A mnemonic: "Trust, Ticket, Talk securely!" helps recall the flow. Reference: MIT Kerberos documentation.

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