CCNA Cryptography Questions

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.

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.

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.

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.

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.

Counter Mode generates a keystream by encrypting successive counter values, so ciphertext blocks have no dependency on one another. That independence enables parallel encryption and decryption and permits retrieval of arbitrary archive segments without reading the whole stream, which matches the constrained tape appliance. CTR provides confidentiality only, so a separate integrity mechanism would be needed if tamper detection matters for the archive.

To create a digital signature with RSA, the sender must hash the message using a collision-resistant hash function and then sign that hash with their private key. This provides integrity (via the hash), authenticity and non-repudiation (via the private key signature). The recipient can verify by hashing the message and decrypting the signature with the sender's public key.

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.

dm-crypt with LUKS is the standard Linux solution for block device encryption. dm-crypt provides the kernel-level encryption, while LUKS provides a standardized header and key management, allowing multiple passphrases to unlock the encryption key. This directly meets the requirement of encrypting a block device with a passphrase-protected key.

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.

Keeping the CA private key generated within and never exportable from the HSM's tamper-protected boundary ensures that even root compromise of the host operating system cannot yield plaintext key material. Signing occurs inside the module, so the key is never exposed to the host. Validation levels and secret-sharing schemes address adjacent concerns but do not prevent plaintext exposure to a privileged local attacker.

A valid detached PGP signature verified with the vendor's trusted public key simultaneously proves that the file content is unchanged and that it was signed by the vendor's private key. The hash comparison alone provides integrity but not origin, and encryption or antivirus scanning addresses entirely different concerns. The public key must be obtained and validated through a trusted channel.

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.

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.