CompTIA Security+ Question K-63

Which of the following could cause a browser to display the message below?
“The security certificate presented by this website was issued for a different website’s address.”

A. The website certificate was issued by a different CA than what the browser recognizes in its trusted CAs.
B. The website is using a wildcard certificate issued for the company’s domain.
C. HTTPS://127.0.01 was used instead of HTTPS://localhost.
D. The website is using an expired self signed certificate.

Answer: C

Explanation:
PKI is a two-key, asymmetric system with four main components: certificate authority (CA), registration authority (RA), RSA (the encryption algorithm), and digital certificates. In typical public key infrastructure (PKI) arrangements, a digital signature from a certificate authority (CA) attests that a particular public key certificate is valid (i.e., contains correct information). Users, or their software on their behalf, check that the private key used to sign some certificate matches the public key in the CA’s certificate. Since CA certificates are often signed by other, “higher-ranking,” CAs, there must necessarily be a highest CA, which provides the ultimate in attestation authority in that particular PKI scheme. Localhost is a hostname that means this computer and may be used to access the computer’s own network services via its loopback network interface. Using the loopback interface bypasses local network interface hardware. In this case the HTTPS://127.0.01 was used and not HTTPS//localhost

CompTIA Security+ Question K-2

Peter, an employee, needs a certificate to encrypt data. Which of the following would issue Peter a certificate?

A. Certification authority
B. Key escrow
C. Certificate revocation list
D. Registration authority

Answer: A

Explanation:
A certificate authority (CA) is an organization that is responsible for issuing, revoking, and distributing certificates.

CompTIA Security+ Question J-100

Which of the following BEST describes part of the PKI process?

A. User1 decrypts data with User2’s private key
B. User1 hashes data with User2’s public key
C. User1 hashes data with User2’s private key
D. User1 encrypts data with User2’s public key

Answer: D

Explanation:
In a PKI the sender encrypts the data using the receiver’s public key. The receiver decrypts the data using his own private key. PKI is a two-key, asymmetric system with four main components: certificate authority (CA), registration authority (RA), RSA (the encryption algorithm), and digital certificates. Messages are encrypted with a public key and decrypted with a private key. A PKI example: You want to send an encrypted message to Jordan, so you request his public key. Jordan responds by sending you that key. You use the public key he sends you to encrypt the message. You send the message to him.

Jordan uses his private key to decrypt the message.

CompTIA Security+ Question H-70

Company A sends a PGP encrypted file to company B. If company A used company B’s public key to encrypt the file, which of the following should be used to decrypt data at company B?

A. Registration
B. Public key
C. CRLs
D. Private key

Answer: D

Explanation:
In a PKI the sender encrypts the data using the receiver’s public key. The receiver decrypts the data using his own private key.

PKI is a two-key, asymmetric system with four main components: certificate authority (CA), registration authority (RA), RSA (the encryption algorithm), and digital certificates. Messages are encrypted with a public key and decrypted with a private key. A PKI example: You want to send an encrypted message to Jordan, so you request his public key. Jordan responds by sending you that key. You use the public key he sends you to encrypt the message. You send the message to him. Jordan uses his private key to decrypt the message.

CompTIA Security+ Question G-47

A company’s security administrator wants to manage PKI for internal systems to help reduce costs. Which of the following is the FIRST step the security administrator should take?

A. Install a registration server.
B. Generate shared public and private keys.
C. Install a CA
D. Establish a key escrow policy.

Answer: C

Explanation:
PKI is a two-key, asymmetric system with four main components: certificate authority (CA), registration authority (RA), RSA (the encryption algorithm), and digital certificates. When you implement a PKI you should start by installing a CA.

CompTIA Security+ Question G-27

Which of the following is true about PKI? (Select TWO).

A. When encrypting a message with the public key, only the public key can decrypt it.
B. When encrypting a message with the private key, only the private key can decrypt it.
C. When encrypting a message with the public key, only the CA can decrypt it.
D. When encrypting a message with the public key, only the private key can decrypt it.
E. When encrypting a message with the private key, only the public key can decrypt it.

Answer: D,E

Explanation:
E: You encrypt data with the private key and decrypt with the public key, though the opposite is much more frequent. Public-key cryptography, also known as asymmetric cryptography, is a class of cryptographic protocols based on algorithms that require two separate keys, one of which is secret (or private) and one of which is public. Although different, the two parts of this key pair are mathematically linked.

D: In a PKI the sender encrypts the data using the receiver’s public key. The receiver decrypts the data using his own private key. PKI is a two-key, asymmetric system with four main components: certificate authority (CA), registration authority (RA), RSA (the encryption algorithm), and digital certificates. Messages are encrypted with a public key and decrypted with a private key. A PKI example: You want to send an encrypted message to Jordan, so you request his public key. Jordan responds by sending you that key. You use the public key he sends you to encrypt the message. You send the message to him.

Jordan uses his private key to decrypt the message.