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.

A true random number generator (TRNG) produces outputs derived from nondeterministic physical processes (e.g., thermal noise, oscillator jitter, radioactive decay, or other hardware entropy sources).
Because the underlying phenomenon is not algorithmically determined by an input seed in the same way as a PRNG, repeated "inputs" (or identical conditions from a software perspective) do not yield the same sequence; the outputs vary unpredictably. By contrast, a pseudorandom number generator (PRNG) is deterministic: given the same seed and internal state, it produces the same output sequence, which is useful for repeatability but means security depends on seed secrecy and proper seeding.
"Prime" is not a generator type, and "sequence" is too generic and does not imply nondeterminism. In cryptographic systems, TRNGs (or hardware entropy sources) are often used to seed cryptographically secure PRNGs (CSPRNGs), combining high-quality entropy with efficient generation. Therefore, the generator that can produce different results for the "same input data" is a true random number generator.

Skipjack is a symmetric block cipher historically associated with the Clipper chip initiative. Its defining parameters match the question: it operates on 64-bit blocks and uses an 80-bit key. The other options do not fit those exact sizes. Twofish is a 128-bit block cipher with key sizes up to 256 bits. Blowfish is a
64-bit block cipher, but its key size is variable from 32 up to 448 bits and is not fixed at 80 bits as a defining property. Camellia is a 128-bit block cipher with key sizes of 128, 192, or 256 bits. Skipjack's smaller key size and legacy design make it unsuitable for modern security needs, but the question is purely about identifying the algorithm that matches an 80-bit key and 64-bit blocks. Therefore, the correct answer is Skipjack.

One-way server authentication is the standard model used by most TLS-enabled web services to prove the server's identity to a client. In this model, the server presents an X.509 certificate during the TLS handshake. The client validates the certificate chain to a trusted root CA, checks hostname binding (CN
/SAN), validates validity dates, and may check revocation status. If validation succeeds, the client gains cryptographic assurance that it is communicating with the holder of the private key corresponding to the server certificate's public key, and that the certificate is issued to the expected domain/identity. This proves the server's identity to the customer without requiring the customer to present a certificate.
Mutual authentication would require both client and server to authenticate each other using certificates (commonly in certain enterprise APIs), but the question asks specifically about the web service proving its identity to the customer, which is satisfied by server-only authentication. One-way client authentication is the opposite direction (client proves identity to server). "End-to-end authentication" is a broader concept and not the specific TLS identity proof mechanism described here. Thus, one-way server authentication is the correct choice.

3DES (Triple DES) is a symmetric block cipher that retains DES's 64-bit block size while increasing effective security by applying DES multiple times. The common "two-key 3DES" variant uses two independent 56-bit DES keys (K1 and K2) in an Encrypt-Decrypt-Encrypt (EDE) sequence: Encrypt with K1, Decrypt with K2, then Encrypt again with K1. Because each DES key is 56 bits (ignoring parity bits), the total keying material is 112 bits. This matches the question's "112-bit key size and 64- bit block size." Plain DES uses only a 56-bit effective key and a 64-bit block size, so it does not match the 112-bit key size. AES has a 128-bit block size and key sizes of 128/192/256. IDEA uses a 64-bit block size but has a 128-bit key. Therefore, the correct algorithm is 3DES. Although 3DES improved on DES, it is now considered legacy due to its small 64-bit block size (birthday-bound issues for large data volumes) and performance overhead compared to AES.