Important WGU Introduction to Cryptography Exam Questions

Answer: B

Explanation:

Digital signing of software typically works by hashing the application (or its manifest) and then using the publisher's private key to create a digital signature over that digest. The private key is used because it is secret and uniquely controlled by the publisher; only the publisher should be able to produce a valid signature. Verifiers (customers) use the publisher's public key to validate the signature and confirm that the digest matches the software they received. This yields two key properties: integrity (the software hasn't been altered; any modification changes the digest and breaks verification) and authenticity (the signature proves it came from the private-key holder). Option A incorrectly describes symmetric stream encryption. Option C incorrectly generalizes private-key behavior as ''block encryption.'' Option D is wrong because verification uses the public key, not a private key; also, ''encrypting with private key'' in this context is better understood as signing, not confidentiality encryption. Therefore, the correct rationale is that the asymmetric private key is used to sign the file's digest so the corresponding public key can verify integrity and authenticity.

Answer: A

Explanation:

RC4 is unique among the RC family listed because it is a stream cipher. It generates a pseudorandom keystream and encrypts data by XORing that keystream with plaintext bytes (and decryption is the same XOR operation). This differs from RC5 and RC6, which are block ciphers: they encrypt fixed-size blocks of data through multiple rounds of operations (such as modular addition, XOR, and rotations) using a secret key. The stream-cipher design means RC4 historically fit protocols where data arrives continuously (e.g., early wireless and web encryption) and where simple, fast software implementation was desired. However, stream ciphers demand careful handling of nonces/IVs to avoid keystream reuse; reuse can catastrophically leak plaintext relationships. RC4 also has well-documented statistical biases in its keystream, leading to practical attacks in protocols like WEP and later concerns in TLS, which is why RC4 has been deprecated in modern security standards. Still, from a classification standpoint, ''stream'' is the distinguishing characteristic versus RC5/RC6 being block ciphers.

Answer: D

Explanation:

Asymmetric encryption (also called public key cryptography) uses a pair of mathematically related keys: a public key and a private key. One key is used to encrypt, and the other is used to decrypt, which is the defining ''different keys'' property asked in the question. In the common confidentiality use case, a sender encrypts a message using the recipient's public key, and only the recipient can decrypt it using their private key. This solves the key distribution problem inherent in symmetric encryption, where both parties must securely share the same secret key in advance. Asymmetric systems also enable digital signatures: the private key signs (creates a signature) and the public key verifies it, providing authenticity and integrity. Symmetric encryption, by contrast, uses the same shared key for both encryption and decryption (even though internal round keys may exist, it is still one shared secret). ''Private key'' alone is not a full encryption type, and ''secure'' is a generic description rather than a cryptographic category. Therefore, the correct answer is D. Asymmetric.

Answer: C

Explanation:

The value 51 mod 11 is the remainder after dividing 51 by 11. Modular arithmetic is widely used in cryptography to keep computations within a finite set of residues, such as in RSA where values are taken modulo n, or in Diffie--Hellman where exponents and group elements are reduced modulo a prime. To compute 51 mod 11, find the largest multiple of 11 less than or equal to 51. Multiples of 11 are 11, 22, 33, 44, 55. The closest without exceeding 51 is 44. Subtracting gives 51 44 = 7, so the remainder is 7. Therefore, 51 mod 11 = 7, matching option ''07.'' This remainder is always in the range 0 through 10 because the modulus is 11. Such residue computations underpin the ''wraparound'' behavior that makes modular exponentiation and inverse computations well-defined in cryptographic groups.

Answer: C

Explanation:

Disk/storage encryption protects data at rest by encrypting the contents of a drive so it remains unreadable without the correct authentication and keys. BitLocker (commonly on Windows) and FileVault (commonly on macOS) are well-known software-based full-disk encryption solutions integrated into their operating systems. They encrypt sectors on disk and typically tie key protection to user credentials and, where available, hardware features such as a TPM or secure enclave to reduce key extraction risk. A VPN encrypts network traffic in transit, not disk storage. An HSM is specialized hardware used to generate, store, and protect cryptographic keys and perform crypto operations; it is not a disk encryption product itself. USB encryption hardware refers to hardware-encrypted removable media, not a software solution for a system disk. Therefore, the correct example of a software encryption solution for disk storage is BitLocker and FileVault.