Homework 7 How to generate high-quality true randomness by hand

1. Homework 7 How to generate high-quality true randomness by hand (Proposed by Arnold G. Reinhold) Advisor: Prof. Jen-Chang Liu Graduate Student: Yi-Ching Chen(陳怡靜) 92321527

2. Motive • Generating randomness by computer offers numerous opportunities for error and attack. • Simple dice present an attractive alternative if used properly. • This paper presents a number of techniques for using dice in conjunction with modern cryptographic software. Random number generator

3. Introduction • PGP (Pretty Good Privacy) 提供e-mail和檔案儲存程式的安全認證加密的服務 • Many PGP users choose weak passphrases. • For the users adopting stronger passphrases, Reinhold have developed a Diceware PassphraseGenerator. • Diceware Passphrase • simple technique for creating short, memorable pass-phrases that are highly secure. • requiring no computer hardware or software. Random number generator

4. Diceware Passphrase • The Diceware Passphrase Generator is a word list indexed so that words can be randomly selected by tossing five dice. • The list contains 7776 (= 65)short English words, abbreviations and easy to remember character strings. • Example Random number generator

5. Word List • Rolling five dice and they came up 2, 1, 1, 1, 3, your next pass phrase word would be "cliff". • A printed copy of the word list • format the word list with 4 columns and 54 lines per page. (63 = 454) You will get a neat, 36 page printout in which the first two dice throws are constant for each page. • How long should the passphrase be? • Reinhold would recommend a five word passphrase for use with PGP, ViaCrypt and similar encryption programs. • In general, a four ~ six word passphrase will provide protection. Random number generator

6. Word List • The list can also be used to generate login passwords for multi-user computer services by just concatenating two words • Reinhold recommend adding a random special character between the words, for example "dobbs(heron". Random number generator

7. Why Diceware? • The random word selection process proposed by Peter Kwangjun Suk. • Could be done by computer when Suk posted his word list. • The source code must undergo public review and the object programs have to be distributed in a trustworthy way. • Most users will not bother to authenticate their copy even though it could easily have been be doctored to produce predictable passphrases. • Any password generating program is subject to a whole range of electronic attacks even after a verified copy has been installed on a user's machine. Random number generator

8. Why Diceware? • Diceware approach • tamperproof, easy to understand, platform independent, immune from electronic attack and cryptographically strong. Random number generator

9. Construction of the Diceware Passphrase Generator • Suk's original list had 10760 entries. • Reinhold added some more 3 and 4 character sequences that are easy-to-remember, like "300" and "aaaa", and then trimmed the list to 7776 entries by deleting all but about one in seven of Suk's 3796 six-character words. • The list contains 7776 (= 65)short English words, abbreviations and easy to remember character strings. • The average length of each word is about 4.2 characters. The longest words are six characters. Random number generator

10. Construction of the Diceware Passphrase Generator • The list was alphabetized using Microsoft Excel, which sorts pure numbers ahead of mixed alphanumeric strings. Numerics and special characters were moved to the end of the list. • The index values are all the five-digit base-6 numbers, but with the digits running from 1 to 6 to match dice markings. Random number generator

11. Analysis of the Diceware Passphrase Generator’s Security • Reinhold’s word list • Selecting a word at random from the resulting list has an entropy value of 8.96 (= log2 7776) bits. • The average length of each word is 4.239 characters. • A passphrase generated from this list will average an entropy of 2.11 (= 12.92/4.239) bits per character, not counting the spaces between words. • Suk's original list • 9.28 bits of entropy per word • The average word length was 4.77 characters • 1.95 bits of entropy per character Random number generator

12. Tampering with the Diceware Generator • The Diceware Generator word list is inherently tamper proof. • The possible tampering is to shorten it or to introduce numerous duplicate entries. • Since the entries are numbered and are in alphabetical order, it is easy to detect any such irregularities. When you select a word, check to make sure it is in the proper alphabetical order and is not a duplicate. Random number generator

13. Diceware Tables for Generating Routing Strings • Table 1. Alphanumeric characters • Rolling a pair of dice and look up each roll in the appropriate table. • Example • A roll where the left die is 4 and the right die is 2 results in the letter "T". Random number generator

14. Diceware Tables for Generating Routing Strings • Table 2. Decimal numbers • * = roll again Random number generator

15. Diceware Tables for Generating Routing Strings • Table 3. Hexadecimal numbers • * = roll again Random number generator

16. Diceware Tables for Generating Routing Strings • Table 4. Syllables (Use three dice) Random number generator

17. Diceware Tables for Generating Routing Strings • Table 5. Special characters Random number generator

18. Diceware Tables for Generating Routing Strings • Table 6. Random numbers from 1 to 36 If you need random numbers in a smaller range, just roll again when a number outside your range comes up. For numbers in the range 1 to 216, roll three dice and use this formula: Left die + 6(Middle die - 1) + 36(Right die - 1) Random number generator