Home > Articles

  • Print
  • + Share This
This chapter is from the book


17.1. Let X be an integer variable represented with 64 bits. The probability is Image that X is in the range (0, 216 − 1), the probability is Image that X is in the range (216, 232 − 1), and the probability Image is that X is in the range (232, 264 − 1). Within each range the values are equally likely. Compute the entropy of X.

17.2. A set of equally likely weather messages are: sunny (S), cloudy (C), light rain (L), and heavy rain (H). Given the added information concerning the time of day (morning or afternoon), the probabilities change as follows:


  • a. Find the entropy of the weather message.

  • b. Find the entropy of the message conditioned on the time of day.

17.3. The Hawaiian alphabet has only 12 letters—the vowels, a, e, i, o, u, and the consonants, h, k, l, m, n, p, w. Assume that each vowel occurs with probability 0.116 and that each consonant occurs with probability 0.06. Also assume that the average number of information bits per letter is the same as that for the English language. Calculate the unicity distance for an encrypted Hawaiian message if the key sequence consists of a random permutation of the 12-letter alphabet.

17.4. Estimate the unicity distance for an English language encryption system that uses a key sequence made up of 10 random alphabetic characters:

  • a. Where each key character can be any one of the 26 letters of the alphabet (duplicates are allowed).

  • b. Where the key characters may not have any duplicates.

17.5. Repeat Problem 17.4 for the case where the key sequence is made up of ten integers randomly chosen from the set of numbers 0 to 999.


  • a. Find the unicity distance for a DES system which encrypts 64-bit blocks (eight alphabetic characters) using a 56-bit key.

  • b. What is the effect on the unicity distance in part (a) if the key is increased to 128 bits?

17.7. In Figures 17.8 and 17.9, P-boxes and S-boxes alternate. Is this arrangement any more secure than if all the P-boxes were first grouped together, followed by all the S-boxes similarly grouped together? Justify your answer.

17.8. What is the output of the first iteration of the DES algorithm when the plaintext and the key are each made up of zero sequences?

17.9. Consider the 10-bit plaintext sequence 0 1 0 1 1 0 1 0 0 1 and its corresponding ciphertext sequence 0 1 1 1 0 1 1 0 1 0, where the rightmost bit is the earliest bit. Describe the five-stage linear feedback shift register (LFSR) that produced the key sequence and show the initial state of the register. Is the output sequence of maximal length?

17.10. Following the RSA algorithm and parameters in Example 17.5, compute the encryption key, e, when the decryption key is chosen to be 151.

17.11. Given e and d that satisfy ed modulo- ϕ(n) = 1, and a message that is encoded as an integer number, M, in the range (0, n - 1) such that the gcd (M, n) = 1. Prove that (Me modulo-n)d modulo-n = M.

17.12. Use the RSA scheme to encrypt the message M = 3. Use the prime numbers p = 5 and q = 7. Choose the decryption key, d, to be 11, and calculate the value of the encryption key, e.

17.13. Consider the following for the RSA scheme.

  • a. If the prime numbers are p = 7 and q = 11, list five allowable values for the decryption key, d.

  • b. If the prime numbers are p = 13, q = 31, and the decryption key is d = 37, find the encryption key, e, and describe how you would use it to encrypt the word “DIGITAL.”

17.14. Use the Merkle–Hellman public key scheme with the super-increasing vector, a = 1, 3, 5, 10, 20. Use the following additional parameters: a large prime number M = 51 and a random number W = 37.

  • a. Find the nonsuper-increasing vector, a, to be made public, and encrypt the data vector 1 1 0 1 1.

  • b. Show the steps by which an authorized receiver decrypts the ciphertext.

17.15. Using the Diffie-Hellman (Elgamal variation) protocol, encrypt the message M = 7. The system parameters are n = 17 and g = 3. The recipient s private key is a = 4. Determine the recipient’s public key. For message encryption with the randomly selected k, use k = 2. Verify the accuracy of the ciphertext by performing decryption using the recipient’s private key.

17.16. Find the hexadecimal (hex) value of the message “no” after one round of the IDEA algorithm. The session key in hex notation is = 0002 0003 0002 0003 0002 0003 0002 0003, where the rightmost 4-digit group represents the subkey Z1. For the message “no,” let each ASCII character be represented by a 16-bit data subblock, where “n” = 006E and “o” = 006F.

17.17. In the PGP Example 17.10, the IDEA session key is encrypted using the RSA algorithm. The resulting encrypted session key (in base-10 notation) was: 0000 2227 0000 2704 0753 0001 1278 0272 0001 1405 0272 0001, where the least significant (rightmost) group is group 1. Using the decryption key, decrypt group 11 of this session key using the Square-and-Multiply technique.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020