Abstract:
A method of establishing a trusted path of data and a method of verifying the integrity of data presented for signing to a user of the personalized device in a public-key cryptographic scheme. The method comprises establishing a trusted path between the user and secure module residing on the personalized device. The secure module holds the user&#39;s private key, displays information about the data message directly to the user, and generates the signature only when instructed to do so. The decision whether or not to sign the data message is determined by the user.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a method of establishing trusted communication paths between correspondents in a public-key cryptographic scheme. More particularly, it relates to verification of data integrity before computation of a signature.  
         BACKGROUND OF THE INVENTION  
         [0002]    Electronic commerce is hampered by privacy and security concerns, as there is no reliable way to ensure that the sender of an electronic transmission is in fact who they purport to be. Due to the non-physical nature of the medium, traditional methods of is physically marking the media with a seal or signature, for various business and legal purposes, are not practical. Rather, some mark must be coded into the information itself in order to identify the source and authenticate the contents.  
           [0003]    In business, whether online or face-to-face, the client and the merchant must provide identification, authentication and authorization. Identification is the process that enables recognition of a user described to an automated data processing system and authentication is the act of verifying the claimed identity of an individual, station or originator, and finally authorization is the granting of the right of access to a user, program, or process.  
           [0004]    A solution to the problems of identification, authentication, confidentiality, authentication, integrity and non-repudiation in information systems lies in the field of cryptography. For confidentiality, encryption is used to scramble information sent between users so that eavesdroppers cannot understand the data&#39;s content. Authentication usually employs digital signatures to identify the author of a message such that the recipient of the message can verify the identity of the person who signed the message. Digital signatures can be used in conjunction with passwords or as an alternative to them.  
           [0005]    Message integrity is determined by methods that verify that a message has not been modified, such methods typically employ message digest codes. Non-repudiation describes the creation of cryptographic receipts so that an author of a message cannot falsely deny sending a message. Thus the Internet reveals the full complexity of trust relationships among people, computers, and organizations.  
           [0006]    As mentioned above, one method of authentication involves digital signatures. Digital signatures use public-key cryptographic techniques employing two related keys, a public key and a private key. In public-key cryptography, the public key is made available to anyone who wants to correspond with the owner of the corresponding private key. The public key can be used to verify a message signed with the private key or encrypt messages that can only be decrypted using the private key. The secrecy of messages encrypted this way, and the authenticity of the messages signed this way relies on the security of the private key. Thus, the private key is kept secret by the owner in order to protect the key against unauthorized use.  
           [0007]    Traditionally smart cards have been used as signing tokens for authenticating a user, smartcards are an alternative name for a microprocessor card, in that it refers to a chip card that is ‘smart’. The expression ‘Smart Card’ is used to refer to all types of chip cards, however SMARTCARD® is a registered trademark of Groupmark. Smart cards place digital certificates, cryptographic keys and other information on a PIN-protected token carried by the end-user, which is more secure than storing it on a computer device which may be vulnerable to unauthorized access. All the cryptographic algorithms involving the private key such as digital signatures and key exchanges are performed on the card. By signing transactions in such an environment, users are assured a modicum of integrity and privacy of the data exchanged between each other. The private key need not be revealed outside of the token.  
           [0008]    One of the disadvantages of smartcards is that the owner is not protected from abuse of the smart card. For example, because of the lack of a user interface, such as a display screen, the owner may not be sure about the contents of the actual message being signed with the smartcard. Another drawback of smartcards is that any entity or person in possession of the smartcard and the PIN, who may not be the rightful owner or which may be a malicious application, in effect has knowledge of the private key.  
           [0009]    Another solution is the implementation of a personalized device, such as a wireless application protocol (WAP) capable mobile phone or wireless personal digital assistant (PDA), as a signing token. Such a personalized device can store private key and sign transactions on behalf of its owner. In such a situation, the holder of the personalized device is assumed to be its rightful owner or authorized representative as determined by an appropriate access-control mechanism. The data message may be generated on an external device, such as an external computer, and then presented to the personalized device for signing. Alternatively, the data message can be generated completely on the personalized device. However, there exists substantial risk for fraud in both of these situations.  
           [0010]    With reference to the first situation in which a data message is prepared on a personal computer, or similar, and then conveyed to the personalized device for signing and transmission, integrity of the message may be comprised. In this example, the owner of the personalized device may wish to employ the larger viewing area or the computing power available on a personal computer to browse and assemble the transaction. Once the data message has been assembled on the personal computer, the data is transmitted to the personalized device for signing. The personalized device calculates a signature, and the signed data message is transmitted via the personalized device. The personalized device thus acts both as a signing token and as a transmitting device.  
           [0011]    In this situation, it is assumed that the external computer can be trusted and that this computer does not contain malicious software or has been programmed by unscrupulous individuals to alter the content of the message. Should the data presented for signing be different from that displayed, then the owner of the private key would then sign fraudulent or financially harmful transactions.  
           [0012]    With reference to the second situation, an example of potential fraud will now be described. Suppose that the personalized device operating system becomes corrupted through any number of ways, such as, by unintentionally installed software containing malicious code, script embedded in messages, or by compromise of the personalized device operating system via security holes. This malicious code could then alter the contents of transactions, as described above.  
           [0013]    Indeed, there is greater potential for fraud as transactions could be created, signed, and transmitted without the knowledge of the owner. The non-repudiation of such fraudulently obtained signed transactions would be difficult to contest as prima facie the personalized device&#39;s owner appears to have sanctioned the data message by appending a valid signature.  
           [0014]    Accordingly, it is an object of the present invention to mitigate at least one of the above disadvantages.  
         SUMMARY OF THE INVENTION  
         [0015]    In accordance with one of its aspects, the invention provides a method of establishing a trusted path for data between correspondents in a public-key cryptographic scheme, one of the correspondents being a personalized device. The method also provides a means of verifying the integrity of data presented for signing to the user of the personalized device. In one aspect, the personalized device may be a mobile phone, equipped with an operating system, input/output devices and is provided with a secure module independent of the operating system.  
           [0016]    The secure module is arranged to accept no instructions from the operating system on the personalized device. Accordingly., there is a diminished possibility of compromise of the data prior to signing.  
           [0017]    In order to mitigate the drawbacks of prior art devices, the method of establishing a trusted communication path for data between authenticating device and its user comprises the steps of: logically isolating the secure module from the main processor of the personalized device; storing the private key within the secure module; providing trusted paths between the user and the secure module of the personalized device, such trusted paths may follow the criteria set in FIPS 140-2, the United States Government standard that describes the security requirements for cryptographic hardware and software modules. Coupled to the secure module is a device display, which provides textual and graphical displays that prompt a user for information input. A trusted button facilitates the input of information. The secure display are wholly under the control of the secure module and coupled thereto by secure paths, and the trusted button is in direct communication with the secure module via secure path. Trusted paths reduce the chances of unauthorized and undetected modification of the secure module, including the unauthorized modification, substitution, insertion, and deletion of keys and other critical security parameters.  
           [0018]    Accordingly, possible fraudulent use of the private key is diminished as the user signs only valid and legitimate data. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0019]    These and other features of the preferred embodiments of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:  
         [0020]    [0020]FIG. 1 is a schematic diagram of two correspondents in communication with each other, in which the correspondents are an external computer and a personalized device in ghost outline;  
         [0021]    [0021]FIG. 2 is a schematic diagram of the stand-alone personalized device of FIG. 1, for use in a PKI scheme; and  
         [0022]    [0022]FIG. 3 is a flow chart outlining the steps for authenticating a received message for generation of a signature.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Reference is first made to FIG. 1, which shows a system  10  for verifying the integrity of a data message including a first correspondent  12  and a second correspondent  14  are in communication with each other, in a preferred embodiment. The first correspondent  12  is designated as a personalized device  12  and the second correspondent  14  is designated as an external computer  14 . Preferably, the personalized device  12  is a wireless application protocol (WAP) enabled mobile phone or a wireless personal digital assistant (PDA) such as a Palm Pilot® or a Handspring Visor®. In this embodiment the personalized device  12  is a mobile phone controlled by the device main processor  16  including a secure module  18 .  
         [0024]    The secure module  18  is adapted to operate independently of the device main processor  16 , so that the internal state of the secure module  18  can not be readily reverse engineered and/or that its interactions with the underlying hardware are not maliciously intercepted and reinterpreted. The secure module  18  is programmable through appropriate toolkits to accept only certain types of instructions from underlying hardware, such as the device main processor  16 .  
         [0025]    Coupled to the device main processor  16  is a device display  20 , which provides textual and graphical displays that prompt a user for information input. The input of information is facilitated by a keyboard  22  coupled to the device main processor  16 . Similarly, the secure module  18  is in communication with a secure display  24 , a secure part of display  30 , and a secure input device, preferably a trusted button  26 . The secure display  24  are wholly under the control of the secure module  18  and coupled thereto by secure path  28 , and the trusted button  26  is in direct communication with the secure module  18  via secure path  30 . Thus, the secure paths  28  and  30  are logically isolated and distinct from any other paths. The secure module  18 , the secure I/O devices  24  and  26 , and the secure paths  28  and  30  form trusted paths between said secure module  18  and an user of the personalized device  12 .  
         [0026]    The external computer  14  may be a general computer, a personal computer or a workstation and includes an external display  32 . The data message for authentication is transmitted from the external computer via a communication path to the personalized device  12  and received by the message transceiver  34 . The data message for authentication by the personalized device  12  is communicated from the external computer  14  via communication path  36  or through a wireless air interface to an antenna coupled to the transceiver  34 . Accordingly, the personalized device  12  preferably includes a serial interface, a universal serial bus (USB) interface, an “over the air” interface based on the IEEE 802.11 specification or a BLUETOOTH® interface. Thus, the personalized device  12  can receive data, and can be used to sign a data message generated on the external computer  14 .  
         [0027]    In operation, the external computer  14  assembles the data comprising the portion of the data message to be signed, preferably displaying the appropriate data message on the external display  32 , and conveying the data to the personalized device  12  via the transceiver  34 . The device main processor  16  conveys the data to the secure module  18 , optionally displaying the same data on the display  30 . The secure module  18  displays the data message, or a portion of the message, on the secure display  24  in an appropriate format. In order to verify the integrity of the data, the user compares the data message on the external display  32  and the data message, or portion of it, with the data message on the secure display  24 . If there is a match between the two data messages, the user instructs the secure module  18 , specifically the signature generator to generate a signature by actuating the trusted button  26 . However, if the data messages differ this indicates compromise of the data message conveyed to the secure module  18  and the user can elect not to generate a signature.  
         [0028]    The secure module  18  may be equipped with a verification manager to identify the user using the system  10 . The verification manager determines the access rights and privileges through passwords or biometrics. For example, the external trusted button  26  may also be used to enter a PIN should access control to the secure module  18  be required. For example, in one implementation, the secure module  18  will only generate a signature within a predetermined time period after displaying the data message. Therefore, the external button  26  has to be actuated within the predetermined time period. In order to complete the transaction, the generated signature is conveyed to the device main processor  16  for transmission via the message transceiver  34 . In the event that the external computer  14  attempts to defraud the user of the personalized device  12  by composing a false message or other harmful transaction, the data message output by the secure module  18  will not match with the data message displayed on the external display  32  and the data message will not be authenticated by the user, via the trusted button  26 .  
         [0029]    In another embodiment, the personalized device  12  is a mobile phone and the data message is composed on the personalized device  12 , as shown in FIG. 2. The portion of the data to be signed is displayed on the device display  20 . The secure module  18 , along with its secure display  24  and trusted button  26 , behaves in the same manner as indicated in the preferred embodiment. Upon instruction by the user via the trusted button  26 , a signature is generated and the signed data message is transmitted via the transceiver  34 .  
         [0030]    The method for the verifying the integrity of the data message to determine whether or not to create a signature will now be described, with reference to FIG. 3, which shows a flowchart illustrating the steps employed:  
         [0031]    Step  100 : The secure module  18  accepts data from device main processor  16 , the data comprises the portion of the data message to be signed and may have been assembled on the personalized device  12  or assembled externally by a external computer  14  and then conveyed to the personalized device  12 ;  
         [0032]    Step  110 : The secure module  18  displays the data message on the secure display  24 , and awaits instruction;  
         [0033]    Step  120 : The data message from the main processor  16  is displayed on the device display  20 , and or the external display  32 ;  
         [0034]    Step  130 : The user compares the data message on the device display  20  to the data message on the secure display  24 ;  
         [0035]    Step  140 : A decision is made as to whether there is any correlation between the two data messages, that is, whether the data messages, or portions of the data messages, are logically related to one another;  
         [0036]    Step  150 : If the data message is considered unacceptable, the user instructs the secure module  18  via the trusted instruction path  30  not to calculate a signature; or else  
         [0037]    Step  160 : if the user determines the data message on the secure display  24  to be acceptable, the signature generator in the secure module  18  is instructed via the trusted instruction path  30  by actuating the trusted button  26  to calculate the signature. A further level of assurance may be provided by using the trusted instruction path  30  to enter a PIN and requiring that the secure module  18  does not issue any signatures in the absence of the correct PIN.  
         [0038]    In yet another embodiment, the secure module is software based. In this embodiment, the secure module  18  is a software application running on the device  21  that outputs the data message to a secure portion of the device display  20 , and accepts instructions as input from the device keyboard  22 .  
         [0039]    The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.