GSEC Cryptography — Timed 15 Questions

Question 1

A security analyst is investigating a suspected man-in-the-middle attack against an internal TLS-secured web application. The analyst reviews the certificate chain and notices that the leaf certificate's public key modulus matches an unauthorized external entity. Which fundamental security property of asymmetric cryptography was compromised in this scenario?

15 minute time limit — choose an answer to begin.

Answer

Data confidentiality

Answer

System availability

Answer

Message non-repudiation

Answer

Entity authenticity

Question 2

An organization is updating its public key infrastructure policy to enhance digital signature security and align with modern cryptographic standards. Which TWO actions should the security team implement to achieve robust signature integrity and prevent signature forgery? (Choose two)

Accepted Answer

Migrate all signature generation processes from SHA-1 to SHA-256 or SHA-3 algorithms.. Modern digital signature security requires utilizing strong cryptographic algorithms and adequate key lengths to prevent collision and brute-force attacks. Transitioning away from legacy hash functions like SHA-1 and enforcing robust parameters ensures signatures remain cryptographically verifiable and resistant to sophisticated mathematical attacks over time.

Answer

Replace asymmetric digital signatures entirely with symmetric HMAC tokens.

Answer

Disable certificate revocation list checking to speed up validation performance.

Answer

Store private keys in plain text configuration files on web server root directories.

Question 3

Which cryptographic property ensures that a digital signature remains valid even if the sender's long-term private key is compromised at a later date?

Accepted Answer

Secure Timestamping. Timestamping creates a trusted record of when a document was signed. By using a secure timestamp, an organization can prove the signature was generated while the key was still valid and before any potential revocation. This is critical in legal and financial contexts where the duration of signature validity must be clearly established, ensuring that past signed transactions maintain their non-repudiation and integrity status long after a key might have expired or been replaced.

Answer

Perfect Forward Secrecy

Answer

Certificate Revocation List (CRL)

Answer

Hashing with salt

Question 4

A hospital's compliance team requires that all data at rest on a fleet of Linux servers be encrypted. The servers have no hardware cryptographic accelerators, and the security architect wants to minimize CPU overhead while still using a widely vetted, NIST-approved block cipher. The architect also insists that the chosen mode must not require a separate random IV for each block and must allow parallel decryption. Which AES mode of operation should the architect select?

Accepted Answer

AES-CTR. Counter mode satisfies every stated constraint: it is a NIST-approved AES mode, it does not require a fresh random IV for each block, and it permits parallel decryption because each block is produced independently from the nonce and counter. CBC needs a unique IV per message and serializes decryption, ECB leaks patterns, and GCM adds authentication overhead and nonce requirements.

Answer

AES-ECB

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AES-CBC

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AES-GCM

Question 5

An engineer is configuring an IPsec VPN between two data centers. The requirement is that the VPN must provide confidentiality, data origin authentication, and integrity for the encapsulated packets, and the design must avoid the known weaknesses of using the same key material for both encryption and integrity. Which combination of IPsec protocols and transforms BEST meets this requirement?

Accepted Answer

ESP with AES-CBC for confidentiality and a separate HMAC-SHA-256 for integrity, using distinct keys for each function.. ESP supplies confidentiality while HMAC-SHA-256 supplies integrity and data origin authentication, and deriving separate keys for the two transforms prevents key reuse across cryptographic functions. This satisfies all three stated requirements and aligns with standard IPsec transform guidance. AH alone lacks encryption, and the deprecated 3DES and MD5 pairing violates both algorithm and key-separation requirements.

Answer

ESP with AES-GCM, which derives both the encryption key and the integrity key from the same shared secret without separation.

Answer

ESP with 3DES for confidentiality and HMAC-MD5 for integrity, using the same key for both transforms.

Answer

AH in transport mode with SHA-256 for integrity and no encryption transform.

Question 6

A financial services firm runs an internal certificate authority (CA) that issues TLS certificates for service-to-service authentication. The security team must ensure that if the CA's private key is ever compromised, an attacker cannot forge certificates that appear valid to services that have already cached the CA certificate. Which mechanism best mitigates this risk?

Accepted Answer

Use a hardware security module (HSM) to generate and store the CA private key so the key material never exists in exportable form.. The scenario requires preventing an attacker from forging certificates that already-trusting services accept. If the CA private key is exportable and stolen, the attacker can sign any certificate and those signatures verify against the cached CA certificate. Keeping the key non-exportable inside a hardware security module means signing can only occur through the controlled device, preserving the trust relationship even if the CA host is breached.

Answer

Issue all service certificates from an intermediate CA whose certificate is constrained with a name constraint and a short validity period.

Answer

Enable OCSP stapling on every service so that revocation status is checked at handshake time.

Answer

Use Certificate Transparency logs to publish every issued certificate and monitor for unauthorized issuance.

Question 7

An administrator needs to implement full disk encryption for a fleet of Windows workstations. Which algorithm provides the most robust security posture while maintaining hardware acceleration support in modern CPUs?

Accepted Answer

AES-256 with XTS mode. AES-256 with XTS mode is the industry standard for disk encryption, providing high security against block manipulation attacks. Leveraging hardware-level acceleration via AES-NI instructions ensures that encryption overhead is minimized, preventing performance degradation for end users. This balance of cryptographic strength and operational efficiency is vital for protecting data at rest on mobile devices that are prone to physical theft or unauthorized access attempts.

Answer

DES with CBC mode

Answer

Blowfish with ECB mode

Answer

RSA-4096 with OAEP

Question 8

Refer to the exhibit. An administrator runs this command to generate a certificate signing request. Which security vulnerability is introduced by the inclusion of the -nodes flag in this command?

Accepted Answer

The private key will be stored without passphrase protection. The -nodes flag instructs OpenSSL to generate a private key without a passphrase, leaving it stored in plaintext on the file system. In a production environment, this is critical because an attacker with unauthorized read access to the server's filesystem can immediately compromise the private key. Protecting private keys with a passphrase ensures that even if files are exfiltrated, the keys remain encrypted and unusable without the secret passphrase.

Answer

The RSA key length is insufficient for modern requirements

Answer

The certificate will be self-signed and untrusted

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The output file format defaults to a deprecated encoding

Question 9

A security analyst is investigating a suspected man-in-the-middle attack against an HTTPS service. The analyst finds that the client is ignoring certificate validation errors. Which cryptographic failure is most likely occurring?

Accepted Answer

Improper certificate chain verification. The failure to validate certificates allows an attacker to present a forged certificate that the client blindly trusts. This breaks the fundamental trust model of PKI, allowing an attacker to intercept, inspect, and potentially modify encrypted traffic. This is a common flaw in poorly configured internal applications where developers disable validation to bypass expired or self-signed certificate warnings, creating a significant security hole that leaves users vulnerable to eavesdropping and credential theft.

Answer

Lack of Perfect Forward Secrecy

Answer

Weak cipher suite negotiation

Answer

Use of outdated TLS 1.0 protocol

Question 10

A developer is implementing an application that stores user passwords in a database. Which THREE of the following practices are essential for ensuring the cryptographic security of these stored secrets?

Accepted Answer

Using a unique, random salt for every user. Proper password storage requires a unique salt to prevent rainbow table attacks, a high-work-factor key derivation function to slow down brute-force attempts, and a secure hashing algorithm designed for slow computation. These defenses are mandatory because standard cryptographic hashes like MD5 or SHA-256 are too fast, enabling attackers to perform trillions of guesses per second on modern hardware, making the stored hashes vulnerable to rapid offline cracking if the database is leaked.

Answer

Storing passwords using SHA-256 with no salt

Answer

Encrypting the database table with AES-128

Question 11

An organization is migrating to a cloud environment and must ensure that data remains encrypted while in use by applications. Which technology should the security team implement to achieve this?

Accepted Answer

Homomorphic Encryption. Homomorphic encryption is a sophisticated cryptographic technique that allows computations to be performed on encrypted data without first needing to decrypt it. This ensures that the data is never exposed in cleartext within the application's memory or on the cloud provider's host, effectively providing security for data-in-use. This is a powerful, though performance-intensive, solution for highly regulated industries like finance or healthcare that require data protection even during processing in untrusted environments.

Answer

Transport Layer Security (TLS)

Answer

Full Disk Encryption (FDE)

Answer

Database Transparent Data Encryption

Question 12

A software vendor distributes signed firmware updates to customers. During an incident review, an analyst discovers that an attacker who obtained the vendor's code-signing private key was able to produce updates that passed signature verification on customer devices. The vendor wants to redesign the signing process so that compromise of a single signing key no longer allows an attacker to forge valid updates. Which change best achieves this goal?

Accepted Answer

Require each update to be signed by a threshold of multiple independent keys.. Threshold signing distributes the signing capability across multiple independent keys so that no single compromised key can produce a valid signature. Increasing key size, changing to ECDSA, or adding a transparency log all leave a single key capable of forging updates. Only requiring a quorum of keys changes the trust model so that one stolen key is insufficient.

Answer

Increase the RSA key size from 2048 to 4096 bits.

Answer

Publish the firmware hashes to a public transparency log.

Answer

Switch the signature algorithm from RSA to ECDSA with P-256.

Question 13

A security team is deploying a new internal TLS certificate authority (CA) for service-to-service authentication. The CA private key must be protected, and the team wants to ensure that if the key is compromised, the attacker cannot forge certificates without detection. Which of the following is the MOST effective control to detect unauthorized certificate issuance?

Accepted Answer

Publish all issued certificates to an internal Certificate Transparency (CT) log.. Certificate Transparency logs create a verifiable record of all certificates issued by a CA. By publishing internal certificates to a CT log, the team can monitor for unexpected entries, which would indicate unauthorized issuance. This detective control is more effective than preventive measures like key size or pinning, which do not alert on forgery.

Answer

Enforce a minimum RSA key size of 4096 bits for the CA key pair.

Answer

Require Certificate Revocation List (CRL) checking on all clients.

Answer

Configure certificate pinning in all client applications.

Question 14

A security architect is designing a system that requires cryptographic keys to be generated, stored, and used without ever exposing the private key material to the operating system. The keys must be usable for TLS server authentication and must support high transaction volumes. Which of the following solutions BEST meets these requirements?

Accepted Answer

A Hardware Security Module (HSM) with TLS offloading capabilities.. An HSM provides a dedicated, tamper-resistant environment where private keys are generated and used without ever leaving the device. This ensures the operating system never sees the key material. HSMs are also designed for high-performance cryptographic operations, including TLS acceleration, making them ideal for high-volume server authentication.

Answer

A cloud key management service (KMS) that stores keys in a multi-tenant environment.

Answer

A software-based key store protected by a strong passphrase and file system permissions.

Answer

A Trusted Platform Module (TPM) 2.0 chip on each server.

Question 15

A security analyst is reviewing the configuration of a VPN gateway that uses IPsec in tunnel mode. The analyst notices that the gateway is configured to use IKEv2 with a pre-shared key (PSK) for authentication. Which of the following is the PRIMARY security concern with this configuration?

Accepted Answer

PSK authentication is vulnerable to offline dictionary attacks if an attacker captures the handshake.. Pre-shared key authentication in IKEv2 relies on a secret that is shared among peers. If an attacker captures the authentication exchange, they can attempt to guess the PSK offline, especially if it is weak. This makes PSK authentication vulnerable to dictionary attacks, which is a primary security concern compared to certificate-based authentication.

Answer

PSK authentication cannot be used with IKEv2; it requires IKEv1.

Answer

PSK authentication does not encrypt the IKEv2 handshake, exposing the PSK in plaintext.

Answer

PSK authentication does not provide perfect forward secrecy (PFS).