GSEC Cryptography — 10 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?

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

Answer

Data confidentiality

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System availability

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Message non-repudiation

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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.

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Replace asymmetric digital signatures entirely with symmetric HMAC tokens.

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Disable certificate revocation list checking to speed up validation performance.

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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.

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Perfect Forward Secrecy

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Certificate Revocation List (CRL)

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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.

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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.

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

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

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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.

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

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

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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

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Blowfish with ECB mode

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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.

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The RSA key length is insufficient for modern requirements

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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.

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Lack of Perfect Forward Secrecy

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Weak cipher suite negotiation

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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.

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Storing passwords using SHA-256 with no salt

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Encrypting the database table with AES-128