Unit 2: Symmetric and Public Key Cryptography - Practice Quiz

1 Which command displays the installed OpenSSL version?

2 What does the command openssl rand -hex 16 generate?

3 Which OpenSSL subcommand is commonly used to calculate a SHA-256 digest of a file?

4 Which option is added to an openssl enc command to perform decryption?

5 What is the main output of a cryptographic hash function?

6 Which security property is primarily provided by encryption?

7 What is the purpose of a cryptographically secure pseudorandom number generator?

8 What is a hash collision?

9 What type of cryptographic algorithm is AES?

10 What is the block size used by AES?

11 Which set lists the standard AES key sizes?

12 In AES, which key is normally used to decrypt data encrypted with a secret key?

13 How many related keys are used in asymmetric cryptography?

14 Which key may normally be shared openly in asymmetric cryptography?

15 Which key is normally used to create a digital signature?

16 Which pair contains examples of asymmetric cryptographic algorithms?

17 What commonly links one blockchain block to the previous block?

18 What is a Merkle tree used for in blockchain systems?

19 What do digital signatures help prove for blockchain transactions?

20 What happens to a block's cryptographic hash if the block data is changed?

21 Which OpenSSL command computes the SHA-256 digest of package.bin without modifying the file?

22 A file was encrypted using openssl enc -aes-256-cbc -salt -pbkdf2 -in plain.txt -out cipher.bin. Which command correctly decrypts it?

23 After generating an RSA private key in private.pem, which command extracts its public key into public.pem?

24 A SHA-256 signature is stored in sig.bin. Which command verifies it for message.txt using public.pem?

25 A software publisher wants customers to detect both file modification and malicious replacement of the published digest. Which mechanism is most appropriate?

26 Why is an HMAC generally more suitable than an unkeyed hash for authenticating messages exchanged by two parties sharing a secret?

27 Two plaintexts are encrypted using a stream cipher with the same key and nonce. What relationship can an attacker obtain from the ciphertexts?

28 For an ideal hash function with a 256-bit output, approximately how many random inputs are needed to obtain a collision with significant probability?

29 A system uses AES-192. Which combination correctly describes its block size and key size?

30 When AES-CBC encrypts multiple messages under the same key, which requirement should the initialization vector satisfy?

31 An application decrypting an AES-GCM message finds that its authentication tag is invalid. What should the application do?

32 An encrypted bitmap still reveals repeated visual patterns because identical plaintext blocks produce identical ciphertext blocks. Which AES mode was most likely used?

33 A client must securely send a 50 MB file to a server that has an RSA public key. Which design is most practical?

34 Alice signs a document with her private key. What should Bob use to verify that signature?

35 Why should RSA-OAEP be used instead of applying raw RSA directly to a plaintext?

36 Two parties perform unauthenticated ephemeral Diffie-Hellman over a hostile network. Which improvement directly addresses a man-in-the-middle attack?

37 A blockchain defines each transaction ID as the SHA-256 hash of its serialized transaction. What is the expected effect of changing one byte in the transaction?

38 A balanced Merkle tree contains 1024 transaction leaves. Approximately how many sibling hashes are needed to prove membership of one transaction?

39 What do digital signatures on blockchain transactions primarily provide?

40 An attacker modifies a transaction inside an old block of a hash-linked blockchain. What is the immediate structural consequence?

41 A developer attempts to encrypt a file with openssl enc -aes-256-gcm but OpenSSL reports that the AEAD cipher is unsupported by enc. What is the most accurate explanation?

42 Which OpenSSL command explicitly encrypts m.bin with an RSA public key using OAEP, SHA-256 for OAEP hashing, and SHA-256 for MGF1?

43 A file is encrypted using openssl enc -aes-256-cbc -salt -pbkdf2 -iter 200000. Which security statement is correct?

44 Which algorithm-independent pipeline computes a SHA-256 fingerprint of the DER-encoded SubjectPublicKeyInfo derived from private.pem?

45 For an ideal 256-bit hash, an adversary computes independently distributed hashes. Using the birthday approximation, what is the collision probability?

46 A Merkle–Damgård hash exposes as a MAC, where is a secret prefix. Why is replacing it with HMAC a relevant defense?

47 HKDF-Extract is applied to a human-memorable password using a public random salt. Which conclusion is correct?

48 A system must combine an IND-CPA secure cipher with a secure MAC using independent keys. Which construction most directly provides authenticated encryption under standard composition results?

49 Two different plaintexts are encrypted under AES-GCM with the same key and nonce. What is the most serious consequence?

50 An attacker flips selected bits in CBC ciphertext block for an internal block index . What happens after decryption?

51 Which parameter set correctly describes AES-256?

52 A protocol allocates exactly 32 bits of each AES-CTR input block to a per-message counter and never changes the remaining nonce field during that message. What is the maximum data length before counter wrap must be avoided?

53 Two ECDSA signatures and on distinct message hashes and reuse the same nonce . Assuming inverses exist modulo the group order , which recovery formula is correct?

54 What is the maximum message length that RSAES-OAEP can encode using a 2048-bit RSA modulus and SHA-256, assuming standard OAEP encoding?

55 A protocol accepts an untrusted elliptic-curve public point for an ECDH operation. Which validation most directly prevents invalid-curve and small-subgroup attacks?

56 For textbook RSA, . An attacker chooses invertible and sends to a decryption oracle. What plaintext does the oracle return?

57 A balanced binary Merkle tree contains exactly transaction leaves. Excluding the leaf and root, how large is a standard membership proof if each sibling hash is 32 bytes and the leaf index is supplied separately?

58 An attacker modifies a transaction in an old proof-of-work block and recomputes that block's Merkle root. Which statement best characterizes the remaining obstacle?

59 The same signing key is used by two blockchain protocols whose transaction byte strings may overlap semantically. Which design most directly prevents a valid signature from one protocol being replayed as authorization in the other?

60 In a naive public-key aggregation scheme, an attacker chooses a public key as a function of honest users' public keys so that the aggregate corresponds to a key controlled by the attacker. Which mitigation targets this rogue-key attack?