GSEC Cryptography Application — 10 Questions

Question 1

A security administrator is hardening an SSH server configuration file to protect sensitive administrative access. Which TWO configuration directives must be explicitly enforced to ensure strong cryptographic controls and prevent legacy weak encryption algorithms? (Choose two)

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com. Modern SSH hardening requires disabling legacy ciphers and insecure MAC algorithms that are vulnerable to cryptographic collisions or plaintext recovery attacks. Enforcing robust encryption primitives and modern key exchange algorithms ensures that interactive shell sessions remain protected against advanced eavesdropping and active interception threats.

Answer

MACs hmac-md5,hmac-sha1

Answer

PubkeyAuthentication no

Answer

Cipher blowfish-cbc

Question 2

Refer to the exhibit. A security auditor is reviewing the configuration of a legacy signing service. Based on current cryptographic standards, why is this configuration flagged as a high-risk finding?

Accepted Answer

PKCS#1v1.5 is susceptible to padding oracle attacks.. RSA-1024 is no longer considered secure against modern computational capabilities, and PKCS#1v1.5 padding is susceptible to padding oracle attacks. This combination is insufficient for modern digital signatures, which require at least RSA-2048 and more secure padding schemes like PSS. Flagging this is critical because outdated cryptographic foundations allow attackers to forge signatures or perform factoring attacks, compromising the authenticity and non-repudiation of all documents signed by this service.

Answer

The key size is too large for the RSA algorithm, causing latency.

Answer

RSA should only be used for symmetric key storage.

Answer

The JSON format is not compatible with cryptographic standards.

Question 3

A security team is deploying an internal certificate authority (CA) to issue TLS certificates for microservices. They want to automate the enrollment process without manual approval, but the CA must ensure that any issued certificate cannot be used to sign other certificates. The team configures the CA to include the basicConstraints extension with CA:FALSE and pathlen:0. After issuance, a microservice attempts to use its certificate to sign a subordinate certificate. Which statement describes the outcome when a relying party validates the subordinate certificate?

Accepted Answer

The subordinate certificate is rejected because the issuer certificate lacks the CA:TRUE basicConstraints extension.. The microservice certificate is an end-entity certificate because its basicConstraints extension is set to CA:FALSE. When a relying party validates a certificate signed by this microservice, it checks the issuer's basicConstraints and finds that the issuer is not a CA. Therefore, the subordinate certificate is rejected. The pathlen constraint does not apply because the certificate is not a CA.

Answer

The subordinate certificate is rejected because the microservice certificate does not include the keyUsage extension with keyCertSign.

Answer

The subordinate certificate is accepted because the pathlen:0 constraint only limits the depth of the certificate chain, not the ability to sign.

Answer

The subordinate certificate is accepted because the microservice certificate includes a valid digital signature.

Question 4

A financial institution is implementing a digital signature solution for its internal document approval workflow. The security architect must select a cryptographic algorithm that provides non-repudiation and ensures that signatures cannot be forged even if an attacker obtains the public key. The institution also requires that the signature scheme be standardized by NIST and widely supported in commercial off-the-shelf (COTS) products. Which algorithm should the architect choose?

Accepted Answer

RSA with SHA-256. RSA with SHA-256 is a NIST-standardized digital signature algorithm that provides non-repudiation and is widely supported in commercial products. It uses a private key for signing and a public key for verification, so an attacker with the public key cannot forge signatures. ECDSA is also standardized but may have less ubiquitous support in older COTS environments, making RSA the better fit for broad compatibility.

Answer

AES-256-GCM

Answer

HMAC-SHA256

Answer

ECDSA with P-256 and SHA-256

Question 5

A security administrator is configuring encrypted backups for a remote office. The backup software supports AES-256 but requires a mode of operation that allows parallel processing of blocks and does not require the ciphertext to be padded to a multiple of the block size. The administrator must also ensure that identical plaintext blocks do not produce identical ciphertext blocks. Which mode should be selected?

Accepted Answer

Galois/Counter Mode (GCM). The backup software requires a mode that supports parallel block processing, avoids padding, and ensures identical plaintext blocks produce different ciphertext blocks. Galois/Counter Mode (GCM) meets all these criteria because it uses a counter-based keystream that can be parallelized and never repeats for a given key and IV. GCM also adds authentication, which strengthens backup integrity.

Answer

Output Feedback (OFB)

Answer

Electronic Codebook (ECB)

Answer

Cipher Block Chaining (CBC)

Question 6

A security engineer is deploying an encrypted backup appliance that will store archives for ten years. Management requires that the data remain confidential even if the encryption key is later compromised, and that the appliance never need to re-encrypt existing archives when keys are rotated. Which key management approach best meets these requirements?

Accepted Answer

Encrypt each archive with a randomly generated key that is itself encrypted under a key derived from a forward-secret key schedule, where the derivation key is deleted after each epoch so earlier epochs cannot be recomputed.. Forward secrecy protects data already protected by earlier keys: once an epoch's derivation secret is destroyed, no later compromise can recover it. Because every archive carries its own randomly generated encryption key, rotating the schedule never forces re-encryption of stored archives, and compromise of the current key exposes only the current epoch rather than the full ten-year history.

Answer

Derive a per-archive key from a single organization-wide master secret using PBKDF2 with a unique salt, and store the salt with each archive.

Answer

Encrypt each backup archive with a unique randomly generated data encryption key, wrap that key with a long-lived key-encryption key stored in a hardware security module, and store only the wrapped key alongside the archive.

Answer

Use a hybrid scheme: generate a random symmetric key per archive, encrypt the archive with it, then encrypt that key using an ephemeral asymmetric key pair whose private key is destroyed immediately after wrapping.

Question 7

A security engineer is deploying a new VPN concentrator that will use IPsec in tunnel mode. The engineer must ensure that the encryption algorithm provides both confidentiality and authenticity for each packet, and that the same key is never reused for encryption. Which combination of IPsec protocols should be configured?

Accepted Answer

ESP with AES-GCM. The requirement is for an IPsec encryption algorithm that provides both confidentiality and authenticity while avoiding key reuse for encryption. ESP with AES-GCM delivers authenticated encryption in one step, using a counter-based approach that ensures each packet is encrypted with a unique keystream as long as the IV is unique. This meets all criteria and is efficient.

Answer

AH with HMAC-SHA256

Answer

ESP with 3DES and HMAC-MD5

Answer

ESP with AES-CBC and HMAC-SHA256

Question 8

A security team must digitally sign firmware images so that devices can verify authenticity offline for years. The signing key will be kept in an HSM, and the team wants signatures that remain verifiable by devices that only support RSA and ECDSA and cannot perform large modular exponentiations quickly. Which signing approach should the team choose?

Accepted Answer

ECDSA over the NIST P-256 curve with SHA-256, because verification uses small elliptic-curve operations that are fast on constrained hardware.. ECDSA over P-256 delivers signatures that constrained devices can verify using small elliptic-curve operations instead of costly large-modulus exponentiations. Because the devices explicitly support RSA and ECDSA, ECDSA satisfies compatibility while the HSM safeguards the private signing key, giving offline verifiability without exposing the key.

Answer

A 1024-bit RSA signature with SHA-1, because the smaller modulus reduces the exponentiation cost while retaining legacy compatibility.

Answer

RSA-PSS with a 2048-bit modulus and SHA-256, because PSS provides provable security and is widely supported.

Answer

Ed25519 with SHA-512 internally, because it is deterministic and avoids the random nonce problem that affects ECDSA.

Question 9

A security engineer is implementing full-disk encryption on laptops using BitLocker. The organization requires that the encryption key be protected by a hardware module that validates the boot process before releasing the key. Which BitLocker configuration should be used?

Accepted Answer

TPM-only. The requirement is for hardware-based key protection with boot process validation. BitLocker's TPM-only mode uses the TPM to store the key and measure boot components, releasing the key only if the measurements are trusted. This provides seamless protection without additional user interaction, making it the correct choice for the stated scenario.

Answer

TPM + Startup Key

Answer

Password only

Answer

TPM + PIN

Question 10

A security administrator is configuring a new internal certificate authority (CA) to issue certificates for internal servers. The CA must ensure that certificates can be revoked if a private key is compromised, and that clients can verify the revocation status without directly contacting the CA. Which two mechanisms should be implemented? (Choose two.)

Accepted Answer

OCSP Stapling. The CA must support revocation checking that does not require direct client contact with the CA. Certificate Revocation Lists (CRLs) can be downloaded and cached by clients, enabling offline verification. OCSP stapling allows the server to present a time-stamped OCSP response, so clients receive revocation status without contacting the CA. Together, these mechanisms provide efficient and scalable revocation checking.

Answer

Certificate Transparency (CT)

Answer

Online Certificate Status Protocol (OCSP)

Answer

Simple Certificate Enrollment Protocol (SCEP)