Crypto · Fundamentals interview questions

1. A.function like PBKDF2, bcrypt, scrypt, or Argon2 that slowly derives keys/password hashes to resist brute force
2. B.adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
3. C.asymmetric crypto over elliptic curves giving strong security with smaller keys than RSA
4. D.encryption using the same secret key to encrypt and decrypt (e.g. AES)

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1. A.Symmetric encryption
2. B.Hashing vs encryption
3. C.Hash collision
4. D.Plaintext

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1. A.Symmetric encryption — encryption using the same secret key to encrypt and decrypt (e.g. AES)
2. B.Symmetric encryption — algorithms (e.g. ML-KEM/Kyber, ML-DSA) designed to resist attacks from quantum computers
3. C.Symmetric encryption — property where session keys are ephemeral so compromise of a long-term key cannot decrypt past sessions
4. D.Symmetric encryption — data signed with a private key that anyone can verify with the public key for authenticity and integrity

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1. A.the original readable data before it is encrypted
2. B.encryption using a public/private key pair, where one key encrypts and the other decrypts (e.g. RSA, ECC)
3. C.adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
4. D.a 256-bit cryptographic hash from the SHA-2 family, widely used for integrity and signatures

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1. A.Asymmetric encryption
2. B.Key exchange
3. C.Key derivation function (KDF)
4. D.HMAC

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1. A.Asymmetric encryption — key-agreement algorithm letting parties derive a shared secret without transmitting it
2. B.Asymmetric encryption — encryption using a public/private key pair, where one key encrypts and the other decrypts (e.g. RSA, ECC)
3. C.Asymmetric encryption — two distinct inputs producing the same hash digest, undermining integrity guarantees
4. D.Asymmetric encryption — keyed-hash message authentication code providing integrity and authenticity using a shared secret

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1. A.cipher that encrypts data one bit or byte at a time using a keystream (e.g. ChaCha20)
2. B.a number used once to prevent replay attacks and ensure uniqueness in a cryptographic operation
3. C.one-way function mapping arbitrary data to a fixed-size digest that cannot be reversed
4. D.encoding (e.g. Base64) is reversible without a key and provides no confidentiality, unlike encryption

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1. A.Nonce
2. B.Hashing
3. C.Stream cipher
4. D.Post-quantum cryptography

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1. A.Hashing — a 256-bit cryptographic hash from the SHA-2 family, widely used for integrity and signatures
2. B.Hashing — data signed with a private key that anyone can verify with the public key for authenticity and integrity
3. C.Hashing — one-way function mapping arbitrary data to a fixed-size digest that cannot be reversed
4. D.Hashing — property where session keys are ephemeral so compromise of a long-term key cannot decrypt past sessions

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1. A.memory-hard password hashing algorithm and winner of the Password Hashing Competition, recommended for new systems
2. B.Advanced Encryption Standard, a widely used symmetric block cipher with 128/192/256-bit keys
3. C.one-way function mapping arbitrary data to a fixed-size digest that cannot be reversed
4. D.a random value combined with a key so identical plaintext blocks encrypt to different ciphertext

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1. A.Nonce
2. B.Diffie-Hellman
3. C.Symmetric encryption
4. D.AES

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1. A.AES — algorithms (e.g. ML-KEM/Kyber, ML-DSA) designed to resist attacks from quantum computers
2. B.AES — Advanced Encryption Standard, a widely used symmetric block cipher with 128/192/256-bit keys
3. C.AES — key-agreement algorithm letting parties derive a shared secret without transmitting it
4. D.AES — the original readable data before it is encrypted

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1. A.adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
2. B.a random value combined with a key so identical plaintext blocks encrypt to different ciphertext
3. C.a 256-bit cryptographic hash from the SHA-2 family, widely used for integrity and signatures
4. D.data signed with a private key that anyone can verify with the public key for authenticity and integrity

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1. A.SHA-256
2. B.Diffie-Hellman
3. C.Padding oracle attack
4. D.ECB mode weakness

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1. A.SHA-256 — encryption using a public/private key pair, where one key encrypts and the other decrypts (e.g. RSA, ECC)
2. B.SHA-256 — a 256-bit cryptographic hash from the SHA-2 family, widely used for integrity and signatures
3. C.SHA-256 — periodically replacing cryptographic keys to limit exposure from a potential compromise
4. D.SHA-256 — Advanced Encryption Standard, a widely used symmetric block cipher with 128/192/256-bit keys

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1. A.two distinct inputs producing the same hash digest, undermining integrity guarantees
2. B.encoding (e.g. Base64) is reversible without a key and provides no confidentiality, unlike encryption
3. C.a number used once to prevent replay attacks and ensure uniqueness in a cryptographic operation
4. D.the scrambled output produced by encrypting plaintext

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1. A.Plaintext
2. B.Perfect forward secrecy
3. C.HMAC
4. D.Encoding vs encryption

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1. A.Encoding vs encryption — adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
2. B.Encoding vs encryption — encoding (e.g. Base64) is reversible without a key and provides no confidentiality, unlike encryption
3. C.Encoding vs encryption — memory-hard password hashing algorithm and winner of the Password Hashing Competition, recommended for new systems
4. D.Encoding vs encryption — encryption using the same secret key to encrypt and decrypt (e.g. AES)

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1. A.adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
2. B.exploiting decryption error responses to recover plaintext from CBC-mode ciphertext
3. C.protocol allowing two parties to agree on a shared secret over an insecure channel (e.g. Diffie-Hellman)
4. D.encoding (e.g. Base64) is reversible without a key and provides no confidentiality, unlike encryption

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1. A.Diffie-Hellman
2. B.Authenticated encryption (AEAD)
3. C.Salting
4. D.Block cipher

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1. A.Salting — two distinct inputs producing the same hash digest, undermining integrity guarantees
2. B.Salting — encoding (e.g. Base64) is reversible without a key and provides no confidentiality, unlike encryption
3. C.Salting — adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
4. D.Salting — a random value combined with a key so identical plaintext blocks encrypt to different ciphertext

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1. A.keyed-hash message authentication code providing integrity and authenticity using a shared secret
2. B.cipher that encrypts data one bit or byte at a time using a keystream (e.g. ChaCha20)
3. C.function like PBKDF2, bcrypt, scrypt, or Argon2 that slowly derives keys/password hashes to resist brute force
4. D.cipher that encrypts fixed-size blocks of data, requiring a mode of operation for longer messages

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1. A.Stream cipher
2. B.Block cipher
3. C.Initialization Vector (IV)
4. D.HMAC

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1. A.HMAC — asymmetric crypto over elliptic curves giving strong security with smaller keys than RSA
2. B.HMAC — periodically replacing cryptographic keys to limit exposure from a potential compromise
3. C.HMAC — hashing is one-way and keyless; encryption is reversible with the correct key
4. D.HMAC — keyed-hash message authentication code providing integrity and authenticity using a shared secret

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1. A.algorithms (e.g. ML-KEM/Kyber, ML-DSA) designed to resist attacks from quantum computers
2. B.encryption using a public/private key pair, where one key encrypts and the other decrypts (e.g. RSA, ECC)
3. C.adding a unique random value to each password before hashing to defeat precomputed/rainbow-table attacks
4. D.data signed with a private key that anyone can verify with the public key for authenticity and integrity

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1. A.Digital signature
2. B.Nonce
3. C.Perfect forward secrecy
4. D.Key rotation

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1. A.Digital signature — cipher that encrypts fixed-size blocks of data, requiring a mode of operation for longer messages
2. B.Digital signature — two distinct inputs producing the same hash digest, undermining integrity guarantees
3. C.Digital signature — data signed with a private key that anyone can verify with the public key for authenticity and integrity
4. D.Digital signature — a random value combined with a key so identical plaintext blocks encrypt to different ciphertext

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1. A.hashing is one-way and keyless; encryption is reversible with the correct key
2. B.a number used once to prevent replay attacks and ensure uniqueness in a cryptographic operation
3. C.keyed-hash message authentication code providing integrity and authenticity using a shared secret
4. D.cipher that encrypts data one bit or byte at a time using a keystream (e.g. ChaCha20)

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1. A.Hashing
2. B.Nonce
3. C.Initialization Vector (IV)
4. D.Argon2

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1. A.Nonce — a number used once to prevent replay attacks and ensure uniqueness in a cryptographic operation
2. B.Nonce — two distinct inputs producing the same hash digest, undermining integrity guarantees
3. C.Nonce — algorithms (e.g. ML-KEM/Kyber, ML-DSA) designed to resist attacks from quantum computers
4. D.Nonce — cipher that encrypts fixed-size blocks of data, requiring a mode of operation for longer messages

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