How to Memorize a Random 60-Bit String

Human Language Technologies: The 2015 Annual Conference of the North American Chapter of the ACL, pages 1569–1575, Denver, Colorado, May 31 – June 5, 2015. c⃝2015 Association for Computational Linguistics How to Memorize a Random 60-Bit String Marjan Ghazvininejad Information Sciences Institute Department of Computer Science University of Southern California ghazvini@isi.edu Kevin Knight Information Sciences Institute Department of Computer Science University of Southern California knight@isi.edu Abstract User-generated passwords tend to be memo- rable, but not secure. A random, computer- generated 60-bit string is much more secure. However, users cannot memorize random 60- bit strings. In this paper, we investigate meth- ods for converting arbitrary bit strings into En- glish word sequences (both prose and poetry), and we study their memorability and other properties. 1 Introduction Passwords chosen by users (e.g., “Scarlet%2”) are easy to remember, but not secure (Florencio and Herley, 2007). A more secure method is to use a system-assigned 60-bit random password, such as 0010100010100...00101001. However, this string is hard to memorize. In this paper, we convert such strings into English phrases, in order to improve their memorability, using natural language process- ing to select fluent passphrases. Our methods are inspired by an XKCD cartoon1 that proposes to convert a randomly-chosen 44-bit password into a short, nonsensical sequence of En- glish words. The proposed system divides the 44-bit password into four 11-bit chunks, and each chunk provides an index into a 2048-word English dictio- nary. XKCD’s example passphrase is correct horse battery staple: 1http://xkcd.com/936 44-bit password English phrase --------------- -------------- 10101101010 -> correct 10010110101 -> horse 01010101010 -> battery 10110101101 -> staple The four-word sequence is nonsense, but it is easier to memorize than the 44-bit string, and XKCD hy- pothesizes that users can improve memorability by building an image or story around the four words. In this paper, we investigate other methods for converting a system-generated bit string into a mem- orable sequence of English words. Our methods pro- duce whole sentences, e.g. Fox news networks are seeking views from downtown streets. as well as short poems, e.g. Diversity inside replied, Soprano finally reside. We also move to 60-bit passwords, for better secu- rity. One source claims: As of 2011, available commercial prod- ucts claim the ability to test up to 2,800,000,000 passwords a second on a standard desktop computer using a high- end graphics processor.2 If this is correct, a 44-bit password would take one hour to crack, while a 60-bit password would take 11.3 years. Our concrete task is as follows: 2http://en.wikipedia.org/wiki/Password cracking 1569 Method Name Average Number of Words Average Number of Characters AVG LM Score Capacity Sample Passwords XKCD 4 31.2 -62.42 1 fees wesley inmate decentralization photo bros nan plain embarrass debating gaskell jennie First Letter Mnemonic 15 87.7 -61.20 2 · 1051 It makes me think of union pacific resource said it looks like most commercial networks . Some companies keep their windows rolled down so you don’t feel connected to any community . Contains extreme violence and it was a …

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