What Every Prosecutor Should Know About Peer-To-Peer Investigations

Volume 5, Number 1, 2010 C HILD S EXUAL E XPLOITATION P ROGRAM

UNSAFE HAVENS I: I NVESTIGATION AND PROSECUTION OF What Every Prosecutor Should Know TECHNOLOGY -F ACILITATED CHILD SEXUAL EXPLOITATON About Peer-to-Peer Investigations APRIL 19-23, 2010 By Sergeant Josh Moulin, 1 CFCE, DFCP, ACE, CEECS BOCA RATON , F LORIDA This five-day course is designed to familiarize prosecutors with the various eer-to-Peer (P2P) file sharing is one of the trapeer they are connected to without any user interac - stages of an investigation, pre-trial and fastest and easiest ways for individuals tion. case preparation in a technology-facilitated around the world to obtain and trade images One way ultrapeers keep track of files available on and videos of child sexual exploitation. As of their leaves is by maintaining a Distributed Hash Table child sexual exploitation case. October 2007, the Wyoming Internet Crimes (DHT) of the names of all their shared files. Normally Against Children (ICAC) Task Force has captured hash values are a mathematical algorithm that produce a QUAL USTICE OR HILDREN P E J F C : 377,044 unique computers sharing image and movie files huge combination of letters and numbers that are the INVESTIGATION AND containing child sexual exploitation using the Gnutella equivalent of a digital fingerprint for a particular file (such PROSECUTION OF CHILD ABUSE network. 2 If you investigate and prosecute technology-fa - as MD5 or SHA-1). However, when referring to DHT, MAY 17-21, 2010 cilitated crimes against children it is important to under - the hash value created is only for the filename and has CHARLESTON , S OUTH CAROLINA stand P2P and the way that sexual predators use it to nothing to do with the actual content of the file. Equal Justice is a five-day comprehensive exploit children. For example, let’s say the words “Phil” and “Collins” course designed to meet the needs of P2P first received notoriety in 2001, in the A&M create a hash value of three. The words “Phil,” “Collins,” Records v. Napster case, when the 9th Circuit Court of Ap - “In,” “The,” “Air,” “Tonight” create a hash value of nine. frontline child abuse professionals, including peals ruled that Napster was liable for contributory in - When a user searches for the term “Phil Collins” it trans - prosecutors, law enforcement, medical and fringement of record companies’ copyrights and had to lates to the hash of three and the ultrapeers begin looking mental health professionals, SANE/SART pay music creators and copyright owners 26 million dol - for computers with a three in their DHT. Once the table teams, emergency response teams, child lars. 3 The court focused on Napster’s role as a centralized is searched and matching hash values are found, the infor - protection and child advocacy center staff, P2P network; meaning that the data was stored on a cen - mation is populated on a list on the computer that initi - social workers and victim witness advocates. tralized server owned by Napster. 4 The court found that ated the search. For example, if the above search was run, a Conference participants will be taught by because Napster had a direct role in distributing files to list of all the possible files with the hash value of three and have the opportunity to interact with users who were searching for music, they were liable for would appear on the monitor of the computer where the 5 many of the nation’s foremost child abuse copyright infringement. The Napster case taught P2P search was entered. users and developers a major lesson and lead to the evolu - Once the user receives the search results, he or she experts. tion of the decentralized model of P2P networks that ex - must then make a purposeful action to begin the down - ists today. load process. Depending on the software used to access UNSAFE HAVENS II: P ROSECUTING As a result of the decision in the Napster case, today’s the Gnutella network, this step can be accomplished sev - TECHNOLOGY -F ACILITATED CRIMES P2P networks do not utilize a centralized server. This eral ways: double clicking the file, right-clicking it and se - AGAINST CHILDREN means that no one person is responsible for the content of lecting “download,” highlighting several files and clicking AUGUST 23-27, 2010 what is being shared on P2P networks. Additionally, unlike on a download button, and/or any combination of these NATIONAL ADVOCACY CENTER Napster where the company’s server could simply be shut methods. What is important to those involved in investi - COLUMBIA , S OUTH CAROLINA down and the copyright infringement stopped, files are gating or prosecuting individuals possessing child pornog - An advanced trial advocacy course focusing now shared and kept on multiple individual computers. raphy is showing that the user initiated the download. This While multiple P2P networks exist, the Gnutella network action helps establish the element of intent required in on prosecuting technology-facilitated child is a decentralized network that is by far the most popular such cases. sexual exploitation cases from opening and will be the focus of this article. Some other less popu - Gnutella also uses hash values to identify files inde - statements through sentencing. lar but functionally similar P2P networks include Fast - pendent of the filename and to confirm a file has been Track, BitTorrent, eDonkey, and Freenet. completely downloaded. This type of hashing is similar to SAFETY NET : M ULTIDISCIPLINARY what a forensic computer examiner uses, as opposed to INVESTIGATION AND PROSECUTION OF How the Network Works the DHT values mentioned above. Gnutella uses a base 32 TECHNOLOGY -F ACILITATED CHILD Since no centralized server hosts files, the Gnutella net - SHA-1 value to identify its files. This is important for SEXUAL EXPLOITATION work depends on each client computer to share informa - forensic examiners to understand because it is different tion about the files available for other users. When a from the traditional base 16 hash values normally used in SEPTEMBER 27-O CTOBER 1, 2010 computer connects to the Gnutella network it is desig - forensics. If a forensic examiner attempts to “hash” a file STONEHILL COLLEGE nated as either an ultrapeer (sometimes referred to as a su - with traditional forensic software he or she will come up EASTON , M ASSACHUSETTS pernode) or a leaf. Ultrapeers are the backbone of the with a completely different hash value from the base 32 This intensive five-day course is intended Gnutella network and act as traffic cops, directing incom - SHA-1 value Gnutella uses. Free software applications are for prosecutors, investigators and computer ing search requests to the appropriate computers that con - available to convert the base 32 SHA-1 to a base 16 SHA-1. forensic examiners investigating technology- tain files or information that a user wants. Leaves are Returning to our example, when a user attempts to facilitated crimes against children. This computers that do not have the capacity to support the download the song “In the Air Tonight,” Gnutella will not course includes hands on computer lab Gnutella network and that connect to ultrapeers to share look at filenames, but rather, for other computers sharing exercises. files. that file based upon its SHA-1 hash value. If, “In the Air Determining whether a computer is an ultrapeer or Tonight” is being shared by multiple users then it is possi - leaf is based on a number of factors. A computer with a ble for the Gnutella network to obtain parts of the file For more information about these fast Internet connection, not behind a firewall, and with a from several users; instead of the user downloading the conferences, see our Web site at historically stable connection to the Gnutella network entire song from one computer, he or she will get a small www.ndaa.org may be designated an ultrapeer. The average Gnutella user piece from several different users sharing the same file. does not know if his or her computer is an ultrapeer or a This allows a computer to simultaneously download dif - leaf. ferent portions of the song, making the entire download UPDATE is published by the Na - Each ultrapeer may be responsible for up to 30 indi - process faster and more reliable. tional District Attorneys Association’s vidual leaves and for maintaining connections with other Each portion of the file that is retrieved from the National Center for Prosecution of ultrapeers. Ultrapeers help to speed up the Gnutella net - other leaves that are attached to the ultrapeer is then re - work by allowing slower computers (leaves) to connect to assembled as one file on the computer that initiated the Child Abuse. Items may be reprinted an ultrapeer rather than the entire Gnutella network. search. Once the computer that requested the file has if attributed to NDAA’s National While an individual leaf may have slower downloads be - completely downloaded the file, the software (LimeWire, Center for Prosecution of Child cause of connectivity issues, that particular leaf will not BearShare, etc.) will hash the file and compare the down - Abuse. Please provide copies to slow down the other computers connected to the various loaded file’s hash with the hash value of the original file NCPCA . Contact us if you have in - ultrapeers. Additionally, ultrapeers maintain lists of active selected for download. If the hash values match, the Internet Protocol (IP) addresses connected to them and an download is complete and the file is moved into the quiries or article suggestions at index of files being shared. All leaves on the network peri - folder used to store downloaded files. If the file is not 703.549.9222 odically send an index of the files being shared to the ul - completely downloaded, then it is moved into a folder National District Attorneys Association National Center for Prosecution of Child Abuse Non Profit Organization 44 Canal Center Plaza, Suite 110 U.S. Postage Alexandria,Virginia 22314 PAID www.ndaa.org Merrifield,VA Permit No. 795

The National Center for Prosecution of Child Abuse is a program of the National District Attorneys Association. This publication was prepared under Grant No. 2007-JL-FX-K005 from the Bureau of Justice Assistance, DOJ Office of Justice Programs.This information is offered for educational purposes only and is not legal advice. Points of view in this publication are those of the authors and do not necessarily represent the

official position of the U.S. Department of Justice and NDAA.

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y b s m a r g o r p P 2 P n i d e s u s m r e t h c r a e s g n i r e v o c e r m o r f s e m o c e c n e d i v e l a n o i t i d d A o t e l b i s s o p s i t i s m a r g o r p e r a w t f o s e m o s n I . e r a w t f o s P 2 P e h t n i h t i w m o r f t h g i r

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h t g n e l e h t s a l l e w s a n e r d l i h c f o s e g a m i c i h p a r g o n r o p g n i t u b i r t s i d n i d e v l o v n i n e e b . e l i f e m a s t a h t r o f g n i k o o l s r e h t o h t i w d e r a h s

s a h t c e p s u s e h t t a h t h s i l b a t s e o t t n e m e c r o f n e w a l w o l l a l l i w s i h T . n o i t a g i t s e v n i e b n a c d e v i e c e r s a h r e t u p m o c e h t s k n u h c e h t , t i d e d a o l n w o d y l e t e l p m o c t o n e v a h

r e h t o n a g n i r u d d e r u t p a c r e v e s a w t i f i e e s o t e s a b a t a d C A C I e h t t s n i a g a d e k c e h c t u b e l i f a g n i d a o l n w o d f o s s e c o r p e h t n i s i e h s r o e h f i t a h t g n i n a e m , s d a o l n w o d

e b d l u o h s D I U G e h t , n o i t a g i t s e v n i C A C I n a f o t l u s e r e h t s a t r a t s t o n d i d t a h t l a i t r a p e r a h s o t t c e l e s o s l a n a c s r e s U . l a t i v s i n o i t a m r o f n i s i h t , y h p a r g o n r o p d l i h c f o

e s a c P 2 P a s a h r o t a g i t s e v n i n a e r e h w s n o i t a u t i s n I . e r a w t f o s P 2 P e h t f o D I U G e h t n o i s s e s s o p n a h t r e h t a r y h p a r g o n r o p d l i h c f o n o i t a n i m e s s i d f o e g r a h c s u o i r e s t s o m

, d n a ; d e s u n e e b s a h e r a w t f o s P 2 P e h t s e m i t y n a m w o h y l e t a m i x o r p p a ; r e t u p m o c e h t e l i f o t r e h t e h w g n i r e d i s n o c e r a o h w s r o t u c e s o r p r o F . d e r a h s y l l a c i t a m o t u a e b

e h t n o d e l b a n e s a w g n i r a h s r e h t e h w ; s r e d l o f e t e l p m o c n i d n a d e r a h s e h t r o f s h t a p l l i w a l l e t u n G m o r f d e d a o l n w o d s e l i f t a h t r e h r o m i h e s i v d a l l i w d n a r e t u p m o c e h t

e l i f e h t ; e n i h c a m e h t n o n e e b s ’ t i g n o l w o h ; r e t u p m o c e h t n o d e l l a t s n i s i e r a w n o g n i t s i x e y d a e r l a s e l i f e r a h s o t t n a w e h s r o e h f i r e s u e h t s k s a e r a w t f o s e h t s m a r g

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