Patent Application: US-99889007-A

Abstract:
phishing attacks succeed by exploiting a user &# 39 ; s inability to distinguish legitimate websites from spoofed websites . most prior work focuses on assisting the user in making this distinction ; however , users must make the right security decision every time . unfortunately , humans are ill - suited for performing the security checks necessary for secure site identification , and a single mistake may result in a total compromise of the user &# 39 ; s online account . fundamentally , users should be authenticated using information that they cannot readily reveal to malicious parties . placing less reliance on the user during the authentication process enhances security and eliminates many forms of fraud . we disclose using a trusted device to perform mutual authentication that eliminates reliance on perfect user behavior , thwarts man - in - the - middle attacks after setup , and protects a user &# 39 ; s account even in the presence of keyloggers and most forms of spyware .

Description:
in this section , we consider various formulations of the phishing problem and survey phishing tactics , both those in use today and those likely to appear in the near future . we also consider the aspects of user behavior typically exploited by phishing attacks . in this section , we enumerate the goals of an anti - phishing technique , arranged in decreasing order of protection and generality : ensure that a user &# 39 ; s data only goes to the intended recipient . our scheme guarantees the last two goals via technical measures . clearly , an ideal solution would also address the first goal . however , divining a user &# 39 ; s intentions remains a difficult problem , particularly when even the user may find it difficult to quantify his or her precise intentions . the next two goals , while more constrained than the first , require complete control over the user &# 39 ; s data . although we present techniques to assist with the goal of preventing the user &# 39 ; s data from reaching an untrustworthy recipient , ultimately , we cannot guarantee this result , since a determined user can always find some means of disclosing personal information to an adversary . to realize our goals , we assume users can be trusted to correctly identify sites at which they wish to establish accounts . we justify this assumption on the basis of the following observations . first , phishing attacks generally target users with existing accounts . in other words , the phishers attempt to fool a victim with an online account into revealing information that the phishers can use to access that account . second , users typically exercise greater caution when establishing an account than when using the account or when responding to an urgent notice concerning the account . this results in part from the natural analogue of the real world principle of caveat emptor , where consumers are accustomed to exercising caution when selecting the merchants they wish to patronize . however , consumers in the real world are unlikely to encounter a man - in - the - middle attack or an imitation store front , and so they have fewer natural defenses when online . our solution addresses these new threats enabled by the digital marketplace . our approach is largely orthogonal to existing anti - phishing solutions based on heuristics , and it can be combined with these earlier schemes , particularly to protect the user from a phishing attack during the initial account establishment . a typical phishing attack begins with an email to the victim , supposedly from a reputable institution , but actually from the phisher . the text of the message commonly warns the user that a problem exists with the user &# 39 ; s account that must immediately be corrected . the victim is led to a spoofed website designed to resemble the institution &# 39 ; s official website . at this point , the phishing site may launch a passive or an active attack . in a passive attack , the web page prompts the victim to enter account information ( e . g ., username and password ) and may also request other personal details , such as the victim &# 39 ; s social security number , bank account numbers , atm pins , etc . all of this information is relayed to the phisher , who can then use it to plunder the user &# 39 ; s accounts . in an active attack , the phisher may act as a man - in - the - middle attacker , actively relaying information from the legitimate site to the user and back . while early phishing emails typically employed plain text and grammatically incorrect english , current attacks demonstrate increased sophistication . phishing emails and websites often employ the same visual elements as their legitimate counterparts . as a result , spoofed sites and legitimate sites are virtually indistinguishable to users . phishers also exploit a number of dns tricks to further obscure the nature of the attack . the spoofed site may use a domain name like www . ebay . com . kr , which very closely resembles ebay &# 39 ; s actual domain , but instead points to a site in korea . some attacks use obscure url conventions to craft domain names like www . ebay . com @ 192 . 168 . 0 . 5 , while others exploit bugs in the browser &# 39 ; s unicode url parsing and display code to conceal the site &# 39 ; s true domain name [ 21 ]. although most phishing attacks are initiated via email , there are many other potential means of initiation . the phisher could contact the victim via instant messenger , via a popup or other advertisement on another website , or even via fax [ 22 ]. phishers can also exploit mistyped urls by registering domain names like gooogle . com or goggle . com , or even employ techniques to artificially inflate their rankings in search engines . to make matters worse , researchers have discovered automated phishing kits circulating online that enable novice phishers to employ some of these techniques [ 36 ]. attackers have also been quick to exploit attempts at user education . for instance , many users believe that a transaction is secure if they see the ‘ lock ’ icon displayed in the browser window . one possible attack uses javascript to display a spoofed lock image in the appropriate location [ 43 ]. phishers may also acquire their own ssl certificate , relying on users &# 39 ; inability or unwillingness to verify the certificates they install . there have also been cases in which certificate authorities issued certificates to attackers posing as legitimate microsoft employees [ 26 ]. phishers can also try to confuse users by simultaneously loading a legitimate page and a spoofed page using html frames or popups . unfortunately , even these techniques barely scratch the surface of potential phishing scams . despite the advances and innovations discussed above , phishing attacks are continuously evolving into increasingly sophisticated forms . for example , attackers have begun targeting specific individuals within an organization . these highly customized attacks , dubbed spearphishing , often try to trick employees into installing malware or revealing their organizational passwords [ 31 , 23 ]. as a more general form of advanced attack , jakobsson introduces the notion of context - aware phishing in which an attacker exploits some knowledge about the victim in order to enhance the efficacy of the attack [ 19 ]. in a user study , jakobsson found that context - aware phishing attacks dramatically enhanced the probability of a successful attack , from 3 % percent for an ordinary attack to 48 - 96 % for a specially - crafted context - aware attack . another attack variant uses socially - aware phishing . in a socially - aware attack , the phisher uses publicly available information to craft an email that purports to come from someone the victim knows and trusts . to defend against phishing attacks , organizations are in a constant race to detect and take down phishing sites . in the future , this could become even more difficult with distributed phishing attacks [ 20 ], where each page a user visits is hosted at a different location and registered to a different owner . in this section , we consider user - related issues for phishing . some of these observations were also made by dhamija and tygar [ 9 ]. first , users exhibit certain tendencies that inherently undermine security . security is often a secondary concern ; few users start a web browser with the objective of “ doing security .” users want to make purchases , check their accounts and authorize payments online . because of this , users will tend to ignore or , if they become too invasive , circumvent or disable security measures . similarly , users have become habituated to ignoring strange warning boxes that appear when they access secure sites , and they blithely click through such warnings . moreover , prior work shows that humans pick poor passwords with low entropy [ 42 ] and readily volunteer them to complete strangers [ 2 ]. finally , users have become accustomed to computers and websites behaving erratically . they will often attribute the absence of security indicators to non - malicious errors [ 41 ]. in addition , most users cannot distinguish between actual hyperlinks and spoofed hyperlinks that display one url but link to a different url ( i . e ., urls of the form : & lt ; a href =‘ http :// phishing . org /’& gt ; & lt ; img src =‘ ebay - url . jpg ’& gt ; & lt ;/ a & gt ;). furthermore , users are unable to reliably parse and understand domain names or pki certificates . clearly , current technology makes it difficult for even a knowledgeable user to consistently make the right decision , particularly when security is not a primary goal . as a result , we argue that anti - phishing techniques must minimize the user &# 39 ; s security responsibilities . while no automated procedure can provide complete protection , our protocol guards the secrecy and integrity of a user &# 39 ; s existing online accounts so that attacks are no more effective than pre - internet scams ( e . g ., an attacker may still be able to access a user &# 39 ; s account by subverting a company insider ). we base our system on the observation that users should be authenticated using an additional authenticator that they cannot readily reveal to malicious parties . our scheme establishes the additional authenticator on a trusted device , such that an attacker must compromise the device and obtain the user &# 39 ; s password to access the user &# 39 ; s account . the trusted device in our system can take the form of a cellphone , pda , smart watch , usb dongle , smart card , laptop , or even as software on the primary computing platform . in a preferred embodiment described herein , we assume the use of a cellphone . users cannot readily disclose the authenticator on the cellphone to a third party , and servers will refuse to act on instructions received from someone purporting to be a particular user without presenting the proper authenticator . our technique is one of the first systems to prevent active man - in - the - middle attacks . in addition , the use of the cellphone allows us to minimize the effect of hijacked browser windows and facilitates user convenience , because it can be used at multiple machines . we assume that the user can establish a secure connection between their cellphone and their browser and that the cellphone itself has not been compromised . below , we explain how a user creates an account ( or updates an existing account ) using our protocol . we then define the protocol for account usage , as well as steps for recovering if the user &# 39 ; s trusted device is lost or compromised . to enable our system for an online account , the user must ( according to a preferred embodiment ) establish a shared secret with the server . this can be done using one of the out - of - band channels 10 ( see fig2 ) suggested below . these mechanisms for establishing a shared secret rely on institutions to implement measures that ensure 1 ) their new customers are who they say they are , and 2 ) the information in existing customers &# 39 ; files is accurate . institutions have dealt with this problem since well before the existence of computers , and thus , they have well - established techniques for doing so . the out - of - band channel used for establishing a shared secret can take many forms . for example , banks often utilize the postal service as a trusted side - channel . alternatively , a telephone call may suffice . banks could provide the shared secret at atms by displaying the shared secret in the form of a barcode that the user could photograph with the camera on a cellphone [ 25 , 32 ]. as another possibility , initial account setup could be performed on the premises of the financial institution . that way , employees can be trained to assist users with setup ; users &# 39 ; identification can be checked in person ; and users can trust that they are associating with the correct institution . trusted financial institutions could also provide setup services for organizations that lack brick - and - mortar infrastructure , such as online vendors . a preferred embodiment will now be described in conjunction with fig2 and fig4 a . using one of the out - of - band mechanisms 10 discussed above , the institution ( service provider ) sends a randomly chosen secret η to the user . the secret should be of sufficient length ( e . g ., 80 - 128 bits ) to prevent brute - force attacks . the user , using for example a browser 12 on the user &# 39 ; s computer 14 ( i . e ., a first device ), navigates to the institution &# 39 ; s website hosted on a server 16 and initiates setup . the setup steps are summarized in fig2 and described below . the server 16 responds with an account creation message 18 including a specially crafted html tag ( e . g ., & lt ;,— secure - setup —& gt ;), which signals to the browser 12 that account setup has been initiated . the server 16 also authenticates its ssl / tls certificate by including a mac of the certificate , using the shared secret η as a key . the browser 12 contacts a second device ( cellphone 20 ) via bluetooth ( our system is not exclusive to bluetooth . any mechanism that allows the user &# 39 ; s trusted device to communicate with the browser ( e . g ., infrared , 802 . 11 , usb cable , etc .) will suffice ), transmitting the server &# 39 ; s ssl / tls certificate , domain name , site name and mac to the cellphone 20 . the cellphone 20 may be of the type that has a keypad 21 ( seen in fig1 ) and a camera 23 ( seen in fig4 a ). the cellphone 20 is programmed with cryptographic software 22 which prompts the user to confirm the account creation ( to avoid stealth installs by malicious sites ) and enter the shared secret provided by the institution ( if it has not already been entered , e . g ., at the atm or at the financial institution ). the software 22 also verifies the mac on the server &# 39 ; s certificate and aborts the protocol if the verification fails . assuming verification succeeds , the software 22 creates a public / private key pair { k 1 , k 1 − 1 } and saves a record associating the key pair with the server &# 39 ; s certificate , which is also saved . the software 22 creates a secure bookmark entry for the site , using the site &# 39 ; s name and domain name . the cellphone 20 sends a reply message 24 including the new public key authenticated with a mac , using the shared secret as a key , to the server 16 through the user &# 39 ; s computer 14 . the server 16 associates the public key with the user &# 39 ; s account , and henceforward , the client must use the protocol described in the next section to access the online account . all other online attempts to access the account will be denied ( note that this does not preclude a user from conducting business in person , for example .) note that the shared secret provides additional authenticity , but is nevertheless optional . use of a shared secret will likely be required for service providers such as banks . however , some service providers are happy to set up an account as soon as the user provides a credit card . for example , most merchants don &# 39 ; t do any additional checking when a user signs up for an account . in that case , as long as the user arrives at the true merchant site and not a phishing site the very first time , then when the software 22 sets up the key pair , the user will be safe during subsequent visits , even without having used the shared secret to set up the account . once the user &# 39 ; s account has been enabled , the server 16 will refuse access to the account unless the user is properly authenticated via the established public key pair and the user &# 39 ; s credentials , e . g ., a username / password combination . thus , even if the user is tricked into revealing private information to a phisher or a social engineer , the attacker still cannot access the user &# 39 ; s account . according to a preferred embodiment , a user who wishes to access the account will initiate a connection using the browser 12 ( see fig3 ). when the server 16 provides its ssl / tls certificate at 34 in fig3 , the browser 12 forwards the certificate 34 ′ to the cellphone 20 . if the certificate does not match the saved certificate for that server that was previously provided , the cryptographic software 22 closes the browser window and displays a warning message . if the server 16 updates its certificate , then we need a protocol to update the server certificate stored on the cellphone ; for example , the server 16 could send the new certificate along with a signature using the previous private key , and upon successful verification , the cryptographic software 22 can update the certificate it has stored for that server 16 . if the certificate check is successful , the cellphone will prompt the user to select the site she wishes to visit from the list of secure bookmarks 32 on the cellphone 20 shown in fig1 . if the bookmark selected matches the server information provided in message 34 ′, the browser 12 and the server 16 continue to establish an ssl / tls connection [ 11 , 14 ], with cryptographic assistance from the cryptographic software 22 . the cryptographic software 22 assists the browser in performing the client authentication portion of the ssl / tls establishment , using the public key pair associated with this site ( the ssl / tls protocol includes a provision for user authentication , but this is rarely used today ). fig3 summarizes the messages exchanged . essentially , the browser 12 initiates an ssl / tls connection with ephemeral diffie - hellman key agreement . after agreeing on the cryptographic parameters in the hello messages , the server 16 sends at 34 : cert s , g , p , g s mod p , { g , p , g s mod p } ks − 1 ( 1 ) ( i . e ., its certificate , its ephemeral diffie - hellman key information and a signature on the key information ) to the client / user . the browser sends the server &# 39 ; s certificate and domain 34 ′ to the cellphone 20 , and assuming that the certificate check is successful , the browser 12 retrieves the appropriate user certificate cert k1 from the cellphone 20 at 36 . the browser 12 then generates the necessary diffie - hellman key material and calculates a secure hash of the ssl / tls master secret k ( which is based on the derived diffie - hellman key ) and all of the previous handshake messages ( as well as the client &# 39 ; s choice of diffie - hellman key material ), hm , as follows : h = md 5 ( k ∥ pad 2 ∥ md 5 ( hm ∥ k ∥ pad 1 ))∥ sha - 1 ( k ∥ pad 2 ∥ sha - 1 ( hm ∥ k ∥ pad 1 )) ( 2 ) ( where ∥ represents concatenation ) and sends the hash ( h in fig3 ) to the cryptographic software 22 on the cellphone 22 . the cryptographic software 22 replies with a signature on h . note that as long as the cellphone 22 remains uncompromised , an attacker cannot produce this signature , and hence cannot successfully authenticate as the user . the browser 12 forwards the signature to the server 16 , along with the user &# 39 ; s certificate and the client &# 39 ; s diffie - hellman key material at 38 : the browser 12 and the server 16 then exchange the final phase of an ssl / tls negotiation . once the user has been authenticated and the ssl / tls connection has been established , the user may then be prompted to provide the user &# 39 ; s credentials ( e . g ., a user name and user password ). assuming that the user &# 39 ; s credentials are valid , a session is established and the user can use the browser 12 to conduct transactions and account inquiries as usual . note that we do not change the ssl / tls protocol ; we merely use the cellphone 20 to assist the browser ( by providing the user certificate 36 and the signed hash h ) in establishing a session key with the server 16 . an alternative embodiment is shown in fig4 b in which both the browser 12 and cryptographic software 22 are on the same physical device . although this arrangement does not provide as much security as the preferred embodiment illustrated in fig4 a , the embodiment of the fig4 b nonetheless represents one of the many various different ways in which the first device and second device may be implemented . as noted previously , other embodiments could include a pda , smart watch , usb dongle , smart card , or laptop as the second device . inevitably , users will lose or break their cellphones , or replace them with newer models . when this happens , the user must revoke the old keys and establish a new key pair with a new cellphone . in the case of a lost cellphone , revocation prevents an attacker from accessing the user &# 39 ; s accounts . to revoke the old key pairs , we favor using a process that exists today : the user calls the institution via telephone . this is a well - established , familiar process . today , customers already call credit card companies to report the loss of a card and to freeze any transactions on the account . with the loss of a cellphone , users would still call the institutions to revoke their keys . the institution would then send the information needed to establish a new key pair using the techniques described above . we initially considered other methods , such as storing revocation information in the user &# 39 ; s browser or on a usb key . however , telephone calls are superior for three reasons . first , users already know how to call customer service . the reuse of an existing business process reduces the costs — mental and monetary — for all parties . second , cellphones are mobile devices that travel with their users , and users may lose them anywhere . a user whose cellphone is lost on a business trip should act immediately to minimize financial ( or other ) losses ; waiting to access the revocation information stored at home is not acceptable . finally , because revocation information is rarely used , it is easily lost . for example , if revocation information is stored on paper , cd &# 39 ; s , or usb keys , it can be misplaced or damaged . we now describe a prototype of the invention implemented using a cellphone 20 , a web browser 12 and a server 16 as shown in fig4 a . equipping a server with our system requires very minimal changes , namely changes to two configuration options and the addition of two simple perl scripts . from the server &# 39 ; s perspective , our scheme requires no changes to the ssl / tls protocol . indeed , most major web servers , including apache - ssl , apache + mod ssl and microsoft &# 39 ; s iis already include an option for performing client authentication . in our case , we use apache - ssl and enable the sslverifyclient option that indicates that clients may present certificates , but the certificates need not be signed by a trusted certificate authority ( since our client certificates are self - signed ). we also enable the sslexportclientcertificates option that exports information about the client &# 39 ; s certificate to cgi - accessible variables . aside from these two minor configuration changes , we only need two additional cgi scripts ( written in perl ) to implement the server &# 39 ; s side of the protocol . one script handles account creation and writes user information and public keys to a file . when the client attempts to use the account , it provides a self - signed certificate as part of the normal ssl / tls authentication process . the server &# 39 ; s existing ssl / tls module verifies that the signature in the certificate corresponds to the public key enclosed and provides the information in the client &# 39 ; s certificate to the authentication script . the authentication script checks the public key in the certificate against that associated with the user &# 39 ; s account . if the keys match , then the authentication script permits the client to access the site . this approach has several benefits . first , the changes are extremely minor and nonintrusive . second , it still allows legacy clients to establish an ssl / tls connection with the server . the authentication script can then detect whether the client has presented a legitimate certificate . if the script detects a legacy client , it can make a policy decision as to whether to allow the client access to the account , allow restricted access to the account , or redirect the client to the account creation page . on the client side , we use an extension to firefox , an open - source web browser , to detect account creation . when the extension detects a page containing the account creation tag , it signals the cellphone with the appropriate information , and passes the cellphone &# 39 ; s reply to the server . similarly , when the user selects a secure bookmark on the cellphone , the cellphone sends the url to the extension , which redirects the browser to the appropriate site . we also apply a small patch to the firefox code that handles the client authentication portion of the ssl / tls exchange . instead of patching firefox , we could also implement our scheme as an ssl / tls proxy on the user &# 39 ; s computer . this would enable our solution to work with proprietary browsers as well . the patch passes the server &# 39 ; s certificate to the cellphone , along with a hash of the ssl / tls handshake messages and receives from the cellphone a certificate for the user &# 39 ; s public key and a signature on the hash . the browser can then use these items to complete the ssl / tls handshake . by involving the cellphone in the ssl / tls computations , we guarantee that the private key for the account never leaves the phone , preventing even a compromised browser or os from accessing it . our prototype runs on a nokia 6630 cellphone . we developed a java midlet ( an application conforming to the mobile information device profile ( midp ) standard ) that provides the functionality described earlier with a user - friendly interface . a java implementation also simplifies porting the code to other devices . for the cryptographic operations , we use the light - weight cryptography library provided by bouncy castle [ 38 ]. since key generation can require a minute or two , we precompute keys when the user first starts the application , rather than waiting until an account has been created . when the cellphone receives an account creation packet from the browser extension , it selects an unused key pair , assigns it to the server information provided by the browser extension , and then sends the key pair and the appropriate revocation messages to the browser extension . when the user selects a secure bookmark ( see fig1 ), the cellphone sends the appropriate address to the browser extension . it also computes the appropriate signatures during the ssl / tls exchange . a . adams and m . a . sasse . users are not the enemy . communications of the acm , 42 ( 12 ): 40 - 46 , december 1999 . anti - phishing working group . phishing activity trends report . http :// antiphishing . org / apwg phishing activity report august 05 . pdf , august 2005 . n . chou , r . ledesma , y . teraguchi , d . boneh , and j . c . mitchell . client - side defense against web - based identity theft . in ndss , february 2004 . 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