Digital Signatures

Review Questions

You can find the solutions to these questions in Appendix A, "Answers to Review Questions."

1.	Which two of the following are not cryptographic services? Authenticity Confidentiality Integrity Nonrepudiation Resistance against DoS Defense in depth
2.	Which two statements about symmetric encryption are true? Symmetric encryption is a good choice for real-time encryption of bulk data. Symmetric encryption is commonly used to sign asymmetric keys. Symmetric encryption uses asymmetric keys. RSA is an example of a symmetric encryption algorithm. ASE is an example of a symmetric encryption algorithm. With symmetric encryption, the encryption key equals the decryption key.
3.	Which two statements about asymmetric encryption are true? Asymmetric encryption is considerably faster than symmetric encryption. Asymmetric encryption keys should have about half the lifetime of symmetric encryption keys. With asymmetric encryption, the private key can only encrypt data, whereas the public key can only decrypt data. With asymmetric encryption, either of the two keys can be used for encryption and the opposite key can be used for decryption. NSA is an example of an asymmetric encryption algorithm. Asymmetric encryption is often used to create signatures.
4.	Which two statements about hash functions are true? A hash digest can never be reverted to the hashed data. It is computationally difficult to revert a hash digest to the hashed data. Data can be encrypted if hashed with a secret key. Data can be signed by appending a hash of the data. AES can use SHA-1 for data encryption. AES can use MD5 for hashing data.
5.	Which of the following statements does not apply to digital signatures? Digital signatures provide data authenticity. Digital signatures provide data integrity. Digital signatures provide nonrepudiation. Digital signatures do not provide data confidentiality. Digital signatures are based on asymmetric cryptographic algorithms. Digital signatures are created by hashing the result of an asymmetric encryption.
6.	Which of the following represent a more reliable hashing algorithm? DES 3DES AES SHA-1 RSA MD5
7.	You are looking for a method that can prove to others that a certain source sent some data. What cryptography method accomplishes this? Nonrepudiation Authentication Confidentiality Integrity Encryption
8.	Which of the following is not a symmetric encryption algorithm? AES RSA DES Blowfish
9.	When using asymmetric encryption, which key is transmitted from the sending to the receiving host? Public key Private key Shared secret key No keys are transmitted
10.	When using asymmetric encryption, the public key is a reverse encryption algorithm of the private key. What is to keep a host from capturing the public key and generating the opposite algorithm to find the private key? The public key is never communicated to another host. The public key is first encrypted with a shared secret key. Asymmetric keys are always paired with symmetric keys to ensure the algorithm cannot be broken. It is feasibly impossible to find the opposite formula with just the public key.