Abstract:
A method for setting up a secure communication line between a user and a service provider using non-secure communication channels within an insecure network, comprising the steps of transmitting an identity token from a user station to a service provider station both coupled to the insecure network; upon reception of the identity token, triggering the creation of a secret URL by the service provider station; transmitting the secret URL within a secure side channel to the user station; obtaining, within the user station, the secret URL, and setting-up a new communication path in the insecure network linking the user and the service provider station based on said secret URL. Beside discarding a man-in-the-middle by denying him access to the data flow it is also possible to stop him through denying him access to the content of the data flow. Such access can be denied through use of a one-time codebook with semantics only known to the User and the authentication service provider.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    This application is a Divisional Patent Application of U.S. application Ser. No. 11/402,111, filed on Apr. 11, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to cryptography and, more particularly, to the set-up of a secure transmission and/or secure transmission line between a user and a service provider using non-secure communication channels. The invention especially relates to a protocol that prevents phishing and man-in-the-middle attacks including eavesdropping to use the obtained information thereafter. 
         [0004]    2. Description of Related Art 
         [0005]    So-called phising or phishing attacks are a substantial threat for all kinds of transactions based on a secure and authentified access to a server. Economically important types of transactions are so called e-banking, e-voting, e-healthcare and further electronic services. A phishing attack usually comprises the use of social engineering, to fool the user to exchange secret data, e.g. log-on data, with the attacker. The user undertaking such a log-on procedure believes he communicates and exchanges data with the correct provider. The attacker, a man-in-the-middle, uses the transmitted authentication data thereafter or simultaneously to affect a log-on procedure with the service provider under the identity of the attacked authorized user. Following the log-on procedure the attacker than misuses the user&#39;s rights. 
         [0006]    Within this meaning a phishing attack is a classical so called man-in-the-middle attack, which cannot be fend off easily through pure cryptological measures. It is not a very successful measure trying to elucidate the users because it is sufficient that only a very small portion of the users fall for such a social engineering mislead. 
         [0007]    U.S. Pat. No. 6,169,805 provides a method for decrypting at a receiver station a file and uses therefore a side-channel over a conventional PSTN to transmit a key and an identified URL where the crypto software is stored in the insecure network. 
       SUMMARY OF THE INVENTION 
       [0008]    One object of the invention is to provide a fully secure cryptographic technique for enabling privacy of communication between a user and a service provider initially started over non-secure channels. 
         [0009]    It is a further object to set-up a secure communication channel between the user and a service provider while requiring no visible exchange of any cryptographic keys, either public or private. 
         [0010]    Accordingly, it is an object of this invention to allow two par-ties to the communication to exchange the initial set-up messages even though another party (an eavesdropper) intercepts all of their communications. 
         [0011]    It is a further object to set-up a secure communication between the user and a service provider while requiring no visible ex-change of any cryptographic keys, either public or private. 
         [0012]    Accordingly, it is a further object of this invention to allow two parties to the communication to successful exchange information, e.g. transaction information even though another party (an eavesdropper) intercepts all of their communications. 
         [0013]    The successful strategy against phishing attacks is based on a technical solution, which does not depend on the credulity of the users. This strategy does not hamper the availability of services or the ergonomics of the authentication protocol in an undue way. 
         [0014]    The simplest solution of the problem comprises, for every communication, to open ad hoc a new cryptographical secured channel between a user and a service provider (point-to-point https-connection). This happens after the user and, eventually, the service provider had performed a correct authentication. The information to create such a secure channel in order to cut-off any man-in-the-middle attacker has to be secret. The information to be transmitted can be the new secure URL. The creation of the new channel necessitates an user intervention, e.g. choice of a new URL, since the service provider cannot determine with certainty, where the authorized user is located within the network, because there is no secure connection between the IP-address and the user. This means that the new secret URL has to be communicated to the authorized user in a way that a potential attacker has no access to this information. This is equivalent to the statement that only the authorized user can have this dial-up information. 
         [0015]    This can happen through use of a side-channel used to transmit information relating to this secret dial-up information, e.g. card with one-use-URLs, transmission of a SMS, synchronized algorithm to generate an authentication token, calculation based on a seed information with help of a authentication calculator etc. All these solutions allow the transmission of a secret URL (uniform resource locator); they are however potentially unsafe (as a code card), not readily practicable (as a SMS transmission) or unsafe or inflexible (algorithm to generate code). 
         [0016]    The best mode relies on a direct ad hoc transmission of the secret URL address from the service provider to the user, without the possibility for the attacker to obtain the information. This can be realized by transmission of a crypto-container with the URL address into a personal token of the user. Every challenge response authentication protocol or any other protocol with at least one protected transmission channel from the service provider to the user can be used in principle to this purpose. Instead of the usually transmitted one-time-password the URL information is transmitted. The use of said secret URL proves the authenticity of the user. 
         [0017]    Beside the preferred application ensuring that the man-in-the-middle can no longer intercept the data flow, another application is the transmittal of safe information through the man-in-the-middle being still online and listening, wherein a one-time code with secret semantics ensure that the man-in-the-middle cannot use the information he has obtained. Therefore his presence in the line is no longer a problem for the user. 
         [0018]    One preferred embodiment of the invention uses the procedure ac-cording to the above and can be readily implemented using the communication system of EP 1 255 178 and the communication protocol shown in DE 198 59 409. Further different implementations using local readers in combination with smart cards or the use of security token systems (e.g. a time coded calculator as used for the internet banking system by UBS Switzerland or a RSA se-cure ID) are possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Preferred embodiments of the invention will now be described in connection with the accompanying drawings: 
           [0020]      FIG. 1  shows a block diagram of the use of a first protocol according to the invention in the usual environment, wherein the user is not under attack, 
           [0021]      FIG. 2  shows a block diagram of the use of the protocol shown in  FIG. 1  in an environment, wherein the user is under attack, 
           [0022]      FIG. 3  shows a simplified block diagram of the configuration shown in  FIG. 2 , 
           [0023]      FIG. 4  shows a block diagram of the use of a second protocol according to the invention in the usual environment, wherein the user is not under attack, 
           [0024]      FIG. 5  shows a block diagram of the use of the protocol shown in  FIG. 4  in an environment, wherein the user is under attack, and 
           [0025]      FIG. 6  shows a simplified block diagram of the configuration shown in  FIG. 5 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    To ease the reading of this document the entities appearing in the protocols are named after the following schema: 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Entity 
                 Description 
                 Name 
               
               
                   
               
             
             
               
                 AXS-Card 
                 AXS Token used for Authentication 
                 AXS-Card 
               
               
                 User Browser 
                 Internet Browser the user is using 
                 BOB 
               
               
                 Net banking Server 
                 Webserver the net banking runs on (i.e. 
                 BANK 
               
               
                   
                 https://www.somebank.com) 
               
               
                 Authentication Service 
                 AXS Authentication Server 
                 AuSP 
               
               
                 Provider 
               
               
                 Net banking Server for 
                 The webserver which is used for the net banking 
                 ALICE 
               
               
                 SES 
                 (also containing a session URL) (i.e. 
               
               
                   
                 https://sec.somebank.com/123 456) 
               
               
                 Man in the Middle 
                 Webserver running on (https://www.somebank.net) 
                 MALLORY 
               
               
                   
                 rerouting all traffic from the User (BOB) to the real 
               
               
                   
                 server of the bank (https://www.somebank.com) or 
               
               
                   
                 simply listening on the line used by the user 
               
               
                   
               
             
          
         
       
     
         [0027]    The entities stand for functional tasks in the communication process. They may be integrated in one or several computing machines. All identical features receive the same reference de-nominations and numerals throughout the description. 
         [0028]      FIG. 1  shows the use of a first protocol according to the invention in an application for an internet site using HTTP-technology and a browser without an attack “man in the middle”. The protocol runs as follows in the case of the use of a net-banking service: The user (BOB) uses terminal equipment  1  to open the net banking website (e.g. https://www.somebank.com) (BANK) in his browser, which is shown as arrow  21 . BOB enters the AXS-card number (IDT) from the access card  2  as e.g. user-name (can also be something different). The operation of entering data  22  over  21  can be done manually by typing a code from a display on the card  2  or electronically with a smart-card reader of an ASIC within the smart card, a magnetic strip on the card or through emission of radiation in a relevant pattern. In this case the AXS-card number is not a token but an identity claim issued by BOB. In other embodiments this may be a token. 
         [0029]    BANK now creates  23  a unique session URL (SES) (e.g. https://sec.somebank.com/123456) pointing to ALICE. 
         [0030]    SES and IDT are sent  24  to the Authentication Service Provider (AuSP) for an Authentication Request. 
         [0031]    AuSP creates a Challenge (CHAL) and encrypts CHAL and SES with the public key of the logical card (PubX) (i.e. the AXS card). This is sent back  25  to BANK. BANK sends the request  26  more or less unchanged back to BOB. 
         [0032]    Preferably, the browser transmits  27  and  28  the request using the optical interface in the card  2 . Said flickering corresponds to a transmittal of a code, e.g. according to EP 1 255 178. 
         [0033]    However other, simpler approaches can be used. BOB&#39;s internet browser of his terminal equipment  1  can e.g. simply show  27  a code being the equivalent of the flickering, which has than to be, entered manually  28  into the card  2 . 
         [0034]    The card  2  extracts  29  CHAL and SES and displays them in an alphanumerical way, being a URL (unified resource locator). BOB enters  30  SES in the browser of its terminal equipment  1 . The browser opens  31  a new connection to the URL given with SES (ALICE). ALICE sends  32  the login site to BOB. BOB enters  33  CHAL in the login site, and sends  34  it back to ALICE. ALICE sends  35  CHAL to the AuSP. AuSP verifies  36  CHAL and sends  37  the result of the verification back to ALICE. The result can only be “ok” or “not-ok”. If CHAL verified successfully BOB enters  38  the normal net banking site. 
         [0035]    The same procedure is now described with a so called Man in the Middle shown in  FIG. 2 . The protocol runs as follows: The user (BOB) receives e.g. a phishing email from “the man in the middle” (MALLORY) containing a link (https://www.somebank.net) to a site looking like his normal net banking website; but being slightly different as here in the top level domain. Recently it has been demonstrated by Eric Johanson that the Internationalized Domain Names Standard (IDN) comprises a structure enabling an exploit to mislead users in the representation of IDN domain names, if International Domain Name support is enabled in modern browsers, allowing attackers to spoof domain name URLs+SSL certificates. In such a case even the domain name representation is identical to the original web site&#39;s URL. 
         [0036]    But the site opened by clicking the link is not the official net banking site, it is a site on the webserver of MALLORY, which only acts as a proxy. BOB could see the fraud by verifying the server certificate, but this is usually not done and is cumber-some. The invention allows a for a simple counter measure to securely transmit the necessary information to enter the intended web site even through MALLORYs presence. 
         [0037]    BOB enters  21  the AXS-card number (IDT) provided  22  by the card  1  as username (can also be something different as mentioned above). IDT is sent  21  to MALLORY, which sends  211  it unchanged to the official net banking site (BANK). BANK creates  23  a unique session URL (SES) (i.e. https://sec.somebank.com/123456) pointing to ALICE. SES and IDT are sent  24  to the Authentication Service Provider (AuSP) for an Authentication Request. AuSP creates a Challenge (CHAL) and encrypts CHAL and SES with the public key of the logical card (PubX). This is sent  25  back to the BANK. BANK sends  26  the request back to MALLORY which sends  126  it back to BOB. 
         [0038]    BOB&#39;s browser transmits the request using the optical interface into the card  2  as mentioned above or uses another means. The card  2  extracts  29  CHAL and SES and displays  27  and  28  them. BOB then enters  30  SES in his browser. The browser opens  31  a new connection to the URL given with SES (ALICE). At this point MALLORY cannot track the net banking activity of BOB anymore, because the URL provided to BOB is not available to MALLORY. Therefore the remaining procedure is running equivalent to the procedure according to  FIG. 1 , i.e. ALICE sends  32  the login site to BOB. BOB enters  33  CHAL in the login site, and transmits  34  it back to ALICE. ALICE sends  35  CHAL to the AuSP. AuSP verifies  36  CHAL and sends  37  the result of the verification back to ALICE. If CHAL verified  38  successful, BOB enters the normal net banking site. 
         [0039]    The important fact is that MALLORY exploits a less than 100% attentiveness of BOB. As soon as the user is fully authenticated he steals the session and can do whatever he wants. 
         [0040]    Because the new URL for the net banking (ALICE) is sent directly into the card, the “man in the middle” (MALLORY) cannot track the whole net banking session of the user (BOB). The connection from BOB to MALLORY is closed when BOB enters the new URL to ALICE, displayed on the AXS-Card. Starting from that point MALLORY is locked out, because BOB has now a direct channel to ALICE. Even if Mallory spoofs the typed ad hoc URL and tries himself to connect directly to the net banking site he misses the challenge which the user will not submit prior to the established connection with ALICE. 
         [0041]      FIG. 3  shows a simplified block diagram of the configuration shown in  FIG. 2 . The user at the local user infrastructure  1  re-quests a login on a fake service provider web server  4 . This fake service provider web server  4 , together with a fake user terminal equipment  5 , constitutes mainly the raider infrastructure  3  of the man in the middle, MALLORY. 
         [0042]    The login request is communicated within the raider infrastructure  3  to repeat it as a login request from the fake user equipment  5  for the structure  6  of the service provider. The authentication server  7  creates the secret URL and a One Time Password (OTP) and encloses these items within a crypto-container using the public key of the autonomous mobile authentication device  2 . This crypto-container is transmitted to the requesting system, here the man in the middle, who is forced to transmit this container—unreadable to him, to the user station  1 . Through use of smart card technology as described in EP 1 480 107 or EP 1 255 178 the container is detected and decrypted using the key stored in the authentication device  2 , preferably protected by biometric data. The secret URL is extracted and entered into an i/o-device of the user terminal equipment  1 , thus opening a new channel  8  based on the secret URL, reaching towards the true service server  9  within the service provider infrastructure  6 . 
         [0043]    The detection of the container can also be performed within the terminal equipment  2  through the user itself or the information can be passed to an authentication device by different modulated light or acoustic signals, e.g. for a mobile phone being able to provide the URL as output. 
         [0044]    It is also possible to create a different side channel through transmitting of the URL through an SMS or a telephone line. 
         [0045]      FIG. 4  shows the use of a second protocol according to the invention in an application for an internet site using HTTP-technology and a browser without an attack “man in the middle” to transmit an transaction enabling code. The protocol runs as follows in the case of the use of a service asking for some user instructions to validate an action; this might be a banking transaction. 
         [0046]    The parts of this protocol and the related drawings in  FIGS. 4 to 6  being identical to the protocol according to  FIGS. 1 to 3  are only explained in a shorter version. Usually same reference numerals and description terms are used for identical or similar features. 
         [0047]    The user (BOB) uses terminal equipment  1  to open the net banking website (e.g. https://www.somebank.com) (BANK) in his browser, which is shown as arrow  21 . BOB enters the AXS-card number (IDT) from the access card  2  as e.g. username (can also be something different). The operation of entering data  22  over  21  can be done manually by typing a code from a display on the card  2  or electronically with a smart-card reader of an ASIC within the smart card, a magnetic strip on the card or through emission of radiation in a relevant pattern. In this case the AXS-card number is not a token but an identity claim issued by BOB. In other embodiments this may be a token. 
         [0048]    BANK now creates  23  a unique session Codebook (Cx) for BOB. 
         [0049]    Codebook Cx and IDT are sent  24  to the Authentication Service Provider (AuSP) for an Authentication Request. 
         [0050]    AuSP creates a Challenge (CHAL) and encrypts CHAL and Cx with the public key of the logical card (PubX) (i.e. the AXS card). This is sent back  25  to BANK. BANK sends the request  26  more or less unchanged back to BOB. 
         [0051]    Preferably, the browser transmits  27  and  28  the request using the optical interface in the card  2 . Said flickering corresponds to a transmittal of a code, e.g. according to EP 1 255 178. 
         [0052]    The card  2  extracts  29  CHAL and Cx and displays them in an alphanumerical way, being e.g. a list of choices C 1  to Cn from Cx. BOB enters  30  his choice Ca from the possible choices C 1  to Cn in the browser of its terminal equipment  1 . The browser sends this information  31  to the BANK. BANK sends  35  the (unchanged) information to AusP. AuSP verifies  36  CHAL and sends  37  the result of the verification, i.e. the combination of User information and Ca action back to BANK. The BANK interprets  138  Ca on the basis of the onetime code with secret semantics, i.e. the Session Codebook Cx for the User and if this interpretation is verified correct than the transaction Ca is executed for the User and the result is transmitted to his browser  38 . 
         [0053]    The same procedure is now described with a so called Man in the Middle shown in  FIG. 5 . It is assumed that “the man in the middle” (MALLORY) is listening to the traffic coming from the user and that MALLORY is able to transmit corresponding traffic to the User. Such position is usually obtain through procedures called phising (or phishing) but also other alternatives are possible, e.g. a possibility to follow the traffic at a dial-up connection or within the infrastructure of a cable installation, without necessarily interfering within this traffic while gathering information. 
         [0054]    Therefore the webserver of MALLORY can act as a proxy, at least in some instances. However, it is also possible that the eaves-dropper only gathers information for using it later or subsequently through terminating BOB&#39;s access to the net and taking his place. In case that the following description mentions that MALLORY is forwarding something unchanged, MALLORY may be simple eavesdropping (usually before taking over control and acting in-stead of BOB). 
         [0055]    BOB enters  21  the AXS-card number (IDT) provided  22  by the card  1  as username (can also be something different as mentioned above). IDT is sent  21  to MALLORY, which sends  211  it unchanged to the official net banking site (BANK). BANK creates  23  a session Codebook (Cx) for the User and stores it as such. Cx and IDT are sent  24  to the Authentication Service Provider (AuSP) for an Authentication Request. AuSP creates a Challenge (CHAL) and encrypts CHAL and the codebook information Cx with the public key of the logical card (PubX). This is sent  25  back to the BANK. BANK sends  26  the request back to MALLORY which sends it  126  unchanged, i.e. in a transparent way, back to BOB. 
         [0056]    BOB&#39;s browser transmits the request using the optical interface into the card  2  as mentioned above or uses another means. The card  2  extracts  29  CHAL and Cx and displays  27  and  28  them. BOB has now the choice between different options within the n code-book options C 1  to Cn from Cx. He then enters  30  Ca in his browser. The browser transmits  31  this choice to MALLORY. Independent from the attitude MALLORY may have, he cannot evaluate or know the content of this transmission and therefore usually transmit this information unchanged as such. In case he tries to interfere at that point, the following procedure will not be successful and BOB&#39;s choice will not be exceuted but also no other (malevolent) choice can be executed. 
         [0057]    Therefore the remaining procedure is running equivalent to the procedure according to  FIG. 4 , i.e. BANK sends  35  CHAL and the chosen code Ca to the AuSP. AuSP verifies  36  CHAL and sends  37  the result of the verification, i.e. the acknowledgement of the User and the Ca action back to BANK. The BANK interprets  138  Ca on the basis of the onetime code with secret semantics, i.e. the Session Codebook Cx for the User and if this interpretation is verified correct than the transaction Ca is executed for the User and the result is transmitted to his browser  38 . 
         [0058]      FIG. 6  shows a simplified block diagram of the configuration shown in  FIG. 5 . The user at the local user infrastructure  1  re-quests a login on a fake service provider web server  4 . This fake service provider web server  4 , together with a fake user terminal equipment  5 , constitutes mainly the raider infrastructure  3  of the man in the middle, MALLORY. 
         [0059]    The login request is communicated within the raider infrastructure  3  to repeat it as a login request from the fake user equipment  5  for the structure  6  of the service provider. The True Service Provider  9  creates the secret Codebook and transmits it to the authentication server  7  creating a One Time Password (OTP) and encloses these items within a crypto-container using the public key of the autonomous mobile authentication device  2 . This crypto-container is transmitted to the requesting system, here the man in the middle, who is forced to transmit this container—unreadable to him, to the user station  1 . Through use of smart card technology as described in EP 1 480 107 or EP 1 255 178 the container is detected and decrypted using the key stored in the authentication device  2 , preferably protected by biometric data. The secret codebook is extracted and entered into an i/o-device of the user terminal equipment  1 , thus showing the user the n options from C 1  to Cn from the codebook Cx. The user  2  now makes his choice Ca, which in the following does not have a meaning for MALLORY, and reaches it through to the true service server  9  within the service provider infrastructure  6 . If said choice Ca would have been changed to Ca&#39;, AusP will not be able to verify this transaction choice and therefore it would not be executed. 
         [0060]    Within the first embodiment MITM (man in the middle) is stopped and discarded denying him access to the data flow. Within the second embodiment MITM is stopped and (can be) ignored denying him access to the content of the data flow. This access is denied through use of a one-time codebook with semantics only known to the User and AusP.