Abstract:
There is disclosed a method in a communications system for enabling authentication of a sender device and a receiver device in the communication system, wherein the sender device is associated with a self-generated first identity and a first master device, the receiver device is associated with a self-generated second identity and a second master device and wherein the authentication is enabled by utilizing the first master device and the second master device for the sender device and the receiver device to verify the identities of each other. In one embodiment, both the sender device and the receiver device are also associated with a third device ant the third device is used in addition to the master devices for verifying said identities. There is also disclosed a method In a sender device, a method in a receiver device, a method in a third device, a sender device, a receiver device, a third device, and a computer program product for the same.

Description:
TECHNICAL FIELD 
     The present invention relates to digital communications system, and more particularly to methods and devices for enabling authentication in such a digital communications system. 
     BACKGROUND 
     The Internet has revolutionized the way business is done and has changed consumer behavior in a very short space of time. However, electronic commerce will only be able to realize its full potential if a number of important conditions are met. One of these conditions will be the underlying security of the data transported over the Internet, intranets and extranets. 
     Thus, there is an increasing demand for creating secure transfer of packages of information between sender devices and receiver devices in digital communications systems and networks. In areas such as digital business communication, digital money transactions, digital product delivery, etc., it is of importance that the package of information does not fall into the wrong hands, such as in the hands of an unauthorized party, or is tampered with by a participating party or by a third unauthorized party. It is also of importance that the sender and receiver can trust each other. 
     SUMMARY 
     In view of the above-mentioned and other drawbacks of the related art, it would be desirable to achieve an improved method for digital communication and, in particular, an improved method for digital communication in terms of improved security, authentication and/or traceability. Also, it would be advantageous to achieve a communication system comprising at least some of these advantages and/or improvements. In addition it would be advantageous to achieve a sender device and/or a receiver device enabling improved digital communication in terms improved security and/or authentication and/or traceability. 
     To better address one or more of these concerns, in a first aspect of the invention there is provided a method in a communications system. Hence there is provided a method in a communications system for authentication of a sender device and a receiver device in the communication system, wherein the method comprises creating, by the sender device, an identification of the sender device; creating, by the receiver device, an identification of the receiver device; sending, by the sender device, a request pertaining to establishing a relation between the sender device and the receiver device to the receiver device; sending, by the receiver device, at least an identification of a second master device to the sender device; sending, by the sender device, the identification of the second master device to a first master device; sending, from the first master device, a request pertaining to communication conditions needed by the sender device for the sender device to establish communication with the receiver device to the second master device; sending, from the second master device, the communication conditions to the first master device; in a case the sender device fulfills the communication conditions, providing, by the sender device, a first access key to the first master device; and providing, by the receiver device, a second access key to the second master device. 
     The disclosed method may provide for improved digital communication between a sender device and a receiver device since communication between a sender device and a receiver device may involve at least one additional communications device and wherein identification information pertaining to the sender device and the receiver device is communicated to the at least one additional communications device. By means of the at least one additional communications device which may be involved at some stage of the communications between the sender device and the receiver device the digital communication may thus be improved in terms of improved traceability. For the same reasons the digital communication may thus be improved in terms of improved security. For the same reasons the digital communication may thus be improved in terms of improved authentication. For the same reasons the digital communication may thus be improved in terms of improved access rights. 
     The request pertaining to establishing the relation between the sender device and a receiver device to the receiver device may comprise at least an identification of a first group of devices, and wherein the method may further comprise receiving, by the receiver device, the request; sending, by the receiver device, at least an identification of a second group of devices to the sender device; receiving, by the sender device, the identification of a second group; in a case there exists at least one third device, which is a device being one of the devices in both the first group and the second group of devices, sending, by the sender device, a request pertaining to a reference from the at least one third device regarding the receiver device; receiving, by the receiver device, the reference request and sending, by the receiver device, the request to the at least one third device; receiving, by the receiver device, the reference and sending, by the receiver device, the reference to the sender device; receiving, by the sender device, the reference; in response thereto; creating, by the sender device a first public encryption key for establishing communication from the sender device to the receiver device; encrypting, by the sender device, the reference using the first public encryption key; encrypting, by the sender device, the first public encryption key using an additional public encryption key; sending, by the sender device, the encrypted reference and the encrypted first public encryption key to the receiver device; sending, by the receiver device, the encrypted first public encryption key to the at least one third device; decrypting, by the, at least one third device, the encrypted first public encryption key; sending, by the at least one third device, the decrypted first public encryption key to the receiver device; decrypting, by the receiver device, the encrypted reference; validating, by the receiver device, the decrypted reference. 
     The system may further comprise a fourth device and a fifth device, and the sender device may be associated with the fourth device, the receiver device is associated with the fifth device and the fourth device is associated with the fifth device; and wherein in a case there does not exist at least one third device which is a device being one of the devices in both the first group and the second group of devices, the method may comprise sending, by the sender device, a request pertaining to a reference from the fifth device regarding the receiver device, wherein the request is sent to the receiver device; forwarding, by the receiver device, the request to the fifth device; sending, by the fifth device, the reference to the receiver device; forwarding, by the receiver device, the reference to the sender device; sending, by the sender device, the reference to the fourth device; validating, by the fourth device, the reference and sending, by the fourth device, the validated reference to the sender device; creating, by the sender device a first public encryption key for establishing communication from the sender device to the receiver device; encrypting, by the sender device, the reference using the first public encryption key; encrypting, by the sender device, the first public encryption key using an additional public encryption key; sending, by the sender device, the encrypted reference and the encrypted first public encryption key to the receiver device sending, by the receiver device, the encrypted first public encryption key to the fourth device via the fifth device; decrypting, by the fourth device, the encrypted first public encryption key; sending, by the fourth device, the decrypted first public encryption key to the receiver device via the fifth device; decrypting, by the receiver device, the encrypted reference; validating by the receiver device, the decrypted reference. 
     According to a second aspect there is provided a method performed by a sender device for enabling authentication, the method comprising creating an identification of the sender device; sending a request pertaining to establishing a relation between the sender device and a receiver device to the receiver device, wherein the request comprises at least an identification of a first group of devices; receiving at least an identification of a second group of device from the receiver device; in a case there exists at least one common third device in the first group and the second group of devices, sending a request pertaining to a reference from the at least third device regarding the receiver device; receiving the reference from the receiver device; creating a first public encryption key for establishing communication from the sender device to the receiver device; encrypting the reference using the first public encryption key; encrypting the first public encryption key using an additional public encryption key; sending the encrypted reference and the encrypted first public encryption key to the receiver device. 
     The sender device may be associated with a fourth device, the receiver device may be associated with a fifth device and the fourth device may be associated with the fifth device; and wherein in a case there does not exist at least one common third device in the first group and the second group of devices, the method may further comprise sending a request pertaining to a reference from the fourth device regarding the receiver device; wherein the requesting may be forwarded from the fourth device to the fifth device; receiving the reference from the fourth device; creating a first public encryption key for establishing communication from the sender device to the receiver device; encrypting the reference using the first public encryption key; encrypting the first public encryption key using an additional public encryption key; sending the encrypted reference and the encrypted first public encryption key to the receiver device. 
     The reference may comprise a sequence number and the reference may pertain to identification of the receiver device as performed by the third device, and the reference may be associated with the sender device. 
     The first public encryption key may be arranged to be used by the sender device in future communication from the sender device to the receiver device. 
     The method may further comprise creating an additional public encryption key for establishing communication from the sender device to a second receiver device, wherein the additional public encryption key may be different from the first public encryption key. 
     The method may further comprise sending the request pertaining to establishing the relation between the sender device and the receiver device to a first auxiliary device; sending the request pertaining to the reference from the at least third device regarding the receiver device to the first auxiliary device; and sending the encrypted reference and the encrypted first public encryption key to the first auxiliary device. 
     The request pertaining to establishing the relation between the sender device and the receiver device, the request pertaining to the reference from the at least third device regarding the receiver device, and the encrypted reference and the encrypted first public encryption key may further comprise one digital signature, and the digital signature may be associated with the sender device. 
     According to a third aspect there is provided a method performed by a receiver device for enabling authentication, wherein the method comprises creating an identification of the receiver device; receiving a request pertaining to establishing a relation between the receiver device and a sender device from the sender device, wherein the request comprises at least an identification of a first group of devices; sending at least an identification of a second group of devices to the sender device; and in a case there exists at least one common third device in the first group and the second group of devices, sending a request pertaining to a reference from the at least third device regarding the receiver device; sending the reference to the sender device; receiving, by the receiver device, an encrypted reference and an encrypted first public encryption key; sending the encrypted first public encryption key to the at least one third device; receiving a decrypted first public encryption key; decrypting the encrypted reference; and validating the decrypted reference. 
     The sender device may be associated with a fourth device, the receiver device may be associated with a fifth device and the fourth device may be associated with the fifth device; and in a case there does not exist at least one common third device in the first group and the second group of devices, the method may further comprise sending a request pertaining to a reference from the fifth device regarding the receiver device; wherein the requesting is forwarded from the fourth device to, the fifth device; sending the reference to the fifth device; receiving an encrypted reference and an encrypted first public encryption key; sending the encrypted first public encryption key to the fourth device via the fifth device; receiving the decrypted first public encryption key; decrypting the encrypted reference; and validating the decrypted reference. 
     According to a fourth aspect there is provided a method performed by a third device for enabling authentication, wherein the method comprises creating an identification of the third device; receiving a reference request from the receiver device regarding the receiver device; sending, by the third device, the reference to the receiver device; receiving an encrypted first public encryption key; decrypting the encrypted first public encryption key; and sending the decrypted first public encryption key to the receiver device. 
     The reference may pertain to identification of the receiver device as performed by the third device, and the reference may be associated with the sender device. 
     According to a fifth aspect there is provided a communications device which comprises circuitry configured to carry out the method according to any one of the first, second, third or fourth aspects. 
     According to a sixth aspect there is provided a computer program product, comprising computer program code which is stored on a computer-readable storage medium and which, when executed on a processor, carries out a method according to any of the first, second, third or fourth aspects. 
     According to a seventh aspect there is provided method in a communications system for enabling authentication of a sender device and a receiver device in the communication system, wherein the sender device is associated with a first identity, a first master device and a third device; the receiver device is associated with a second identity, a second master device and the third device; and wherein the authentication is enabled by utilizing the first master device, the second master device and the third device for the sender device and the receiver device to verify the identities of each other. 
     According to an eight aspect there is provided a method performed by a sender device for enabling authentication, the method comprising creating an identification of the sender device; sending a request pertaining to establishing a relation between the sender device and a receiver device to the receiver device; receiving at least an identification of a second master device; sending the identification of the second master device to a first master device; receiving a message pertaining to acknowledgement of communication conditions; and in a case the sender device fulfills the communication conditions, providing a first access key to the first master device. 
     According to a ninth aspect there is provided a method performed by a receiver device for enabling authentication, the method comprising creating an identification of the receiver device; receiving a request pertaining to establishing a relation between a sender device and the receiver device; sending at least an identification of a second master device to the sender device; receiving a message pertaining to acknowledgement of communication conditions; and in a case the sender device fulfills communication conditions, providing a second access key to the second master device. 
     The second, third, fourth, fifth, sixth, seventh, eight and ninth aspects may generally have the same features and advantages as the first aspect. 
     The features of the eight aspect may also be features of the second aspect. The features of the ninth aspect may also be features of the third aspect. 
     Other aspects, features and advantages of the disclosed embodiments of the present invention will appear from the following detailed disclosure, from the attached claims as well as from the drawings. 
     Generally, all terms used in the claims, are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described in more detail, reference being made to the enclosed drawings, in which: 
         FIG. 1  is a schematic diagram of a communications system according to an embodiment. 
         FIG. 2  is a schematic diagram of a communications system according to an embodiment. 
         FIG. 3  is a schematic diagram of a communications system according to an embodiment. 
         FIG. 4  is a schematic diagram of a communications system according to an embodiment. 
         FIG. 5  is a schematic diagram of communication system according to an embodiment. 
         FIG. 6  is a flowchart of a method according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Furthermore, like numbers refer to like elements throughout. 
       FIG. 1  shows a schematic diagram of an exemplary communications system  100  in which the disclosed embodiments may be applied. The communications system  100  comprises a number of communication devices  102 ,  104 ,  106 ,  110 ,  112 ,  114  which may or may not be able to communicate with each other. A method in which a first communication device  102 , hereinafter denoted as a sender device  102 , wishes to establish a connection with a second communication device  104 , hereinafter denoted as a receiver device  104 , will be described below. It should be understood that the communication device  102 , is not limited to be a sender device only, it may alternatively be a receiver device or take the role of both a sender device and a receiver device in the communications system  100 . Similarly the communication device  104 , is not limited to be a receiver device only, it may alternatively be a sender device or take the role of both a receiver device and a sender device in the communications system  100 . That is, any communication device within the communication system  100  may include both sender and receiver capability. The sender or receiver devices may also act as a third party device. The functionality of the third party device will be further described below. However, it should be noted that when communications is to be established between a sender device  102  and a receiver device  104 , neither the sender device  102  nor the receiver device  104  may act as a third device in the process of establishing communications between the devices  102  and  104 . 
     In the following it will be assumed that at least part of the system  100  is in a state of operation. 
     When the communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  are connected to the system  100  each communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  may create a unique identification, or identity, to be used in future communications in order to identify said communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 , it should be noted that the unique identity defined by the identification may not be validated by any other communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  in the system  100 . The unique identity is accepted by other devices in the system  100  when a relation, that is, communication, is established. The unique identity is thus used for matching purposes and may not have controlling authority. Moreover, as will be explained below, even if a unique identity of a first device in the system  100  is copied by a second device in the system  100 , or alternatively that the identity of the first device is identical to the identity of the second device by chance, this will not affect the process of establishing a digital relation between two devices in the system  100 . 
     Typically such a unique identity may take the form of a sequence of random binary or integer numbers. The longer the sequence the higher the probability of generating a sequence that is unique for each communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 . The unique identity may alternatively, or additionally, be associated with a serial number of the communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 . 
     A communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  which is able to communicate with other communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  is thus associated with a digital identity. The digital identity may also be associated with a number of references. A reference of a digital identity may pertain to the collated information provided by other communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  regarding the communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  associated with said digital identity. References will be further discussed below. 
     In an initial step the sender device  102  creates an identification of the sender device  102  and the receiver device  104  creates an identification of the receiver device  104 . Typically, the communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  may need to create an identification only once. 
     Each communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  may keep track of each established communication e.g. by means of associating each established communication with a sequence number. The sequence number is associated with the communication device to which a communication was established. 
     In  FIG. 1  solid lines  116 ,  118 ,  120 ,  122 ,  124 ,  126 ,  130  between two communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  represents that communication has previously been established between the two communication devices at each end of the solid line  116 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128 ,  130 . For example, assume that the receiver device  104  has previously established communication with the communication devices  106 ,  110 ,  112  as indicated by the solid lines  130 ,  122 ,  124  in  FIG. 1 . As indicated by the dashed line  132  communications is to be established between the sender device  102  and the receiver device  104 . 
     Assume further that the relative order in which communication was established from the receiver device  104  to the communication devices  106 ,  110 ,  112  was established in the order  106 ,  112 ,  110 . That is, communication was established from the receiver device  104  to the communication device  112  before communication was established from the receiver device  104  to the communication device  110  and after communication was established from the receiver device  104  to the communication device  106 . 
     All sequence numbers of a communication device may be associated with a list of sequence numbers. This list is preferably stored in the communication device. Denote by L 104  the list of sequence numbers for receiver device  104 . Denote further identification information of communication device  108  as interpreted by the sender device  104  as ID( 104 , 106 ) and similarly ID( 104 , 110 ) and ID( 104 , 112 ) for communication devices  110  and  112 , respectively. 
     The sequence number for an established communications from a first communication device to a second communication device may further comprise a number representing the relative order in which the communication was established from the second device to the first device. Assume that communication device  110  established communications with the devices  104 ,  112 ,  114  in the order  112 ,  104 ,  114 . That is, in this exemplary scenario communication from the communication device  110  to the sender device  104  was the second (2nd) established communication from the communication device  110 . Similarly, assume that for in this example communications from the third device  106  to the receiver device  104  was the third (3rd) communication established from the third device  106 ; assume that for in this example communications from the communication device  112  to the receiver device  104  was the fifth (5th) communications established from the third device  112 . 
     In this exemplary scenario the list L( 104 ) of sequence numbers of the receiver device  104  may thus have the form:
     L( 104 )=ID( 104 , 106 ), 3
       ID( 104 , 112 ), 5   ID( 104 , 110 ), 2.   
       

     Thus, utilizing such lists of sequence numbers comprised in the communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  allows for two or more communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  to be associated with the same unique identity without producing conflicting statements in the communications system  100 . 
     Assuming that the sender device  102  wishes to establish a communication with the receiver device  104 , as indicated by the dashed line  132  in  FIG. 1 , the sender device  102  sends a request pertaining to establishing a relation between the sender device  102  and the receiver device  104  to said receiver device  104 . 
     The receiver device  104  then sends at least an identification of a second master device  154  to the sender device  102 . When receiving the identification of the second master device  154  the sender device  102  forwards the identification of the second master  154  device to a first master device  152 . 
     The first master device  152  and the second master device  154  may be viewed as digital notaries. A digital notary may be a company, agency or authority, or the like which may act as notary in digital communications systems and networks. As such the digital notary may provide certified digital witnesses. Digital witnesses will be further disclosed below. The digital notary may also provide archive and/or functionalities and/or means. It may be required that the master devices  152  and  154  are certified by an organization, see below. 
     The first master device  152  then sends a request pertaining to communication conditions to the second master device  154 , which conditions according to the second master device  154  need to be fulfilled in order for the sender device  102  to establish communication with the receiver device  104 . The communication conditions may be associated with a set of values which may pertain to security issues and identification issues. For example the identification issues may relate to communication policies, such as communication protocols, utilized between the sender device  102  and the receiver device  104 . It should be noted that the first master device  152  does not need to communicate an identity of the sender device  102  to the second master device  154 . 
     The second master device  154  then sends the communication conditions to the first master device  152 . In case the sender device  102  fulfills the communication conditions, the first master device  152  may acknowledge to the second master device  154  that the communication conditions are fulfilled. Similarly the first master device may communicate communication conditions to the second master device  154 , which need to be fulfilled by the receiver device  104 , to establish communication with the sender device  102 . 
     A first access key may then be provided by the sender device  102  to the first master device  152 , and a second access key may be provided by the receiver device  104  to the second master device  154 . Thus by utilizing such access keys access rights may be enabled. 
     Communication pertaining to the sender device  102  and the receiver device  104  may then be enabled between the first master device  152  and the second master device  154 . By utilizing the first master device  152  and the second master device  154  authentication of the sender device  102  and the receiver device  104  may be achieved. 
     The request sent from the sender device  102  to the receiver device  104  pertaining to establishing a relation between the sender device  102  and the receiver device  104  may comprises at least an identification of a first group of devices  106 ,  108 . The first group of devices  106 ,  108  is a group of devices with which the sender device  102  has previously established a communication. In this case the disclosed method may continue as follows. The request is received by the receiver device  104 . In response to the request the receiver device  104  analyses the identities of the devices comprised in the first group of devices  106 ,  108  and compares the identities to an intermediate group of devices  106 ,  110 ,  112  to which the receiver device has previously established a communication with. The receiver device  104  then sends at least an identification of a second group of devices to the sender device  102 . The second group of devices comprises the device(s)  106  which are comprised in both the first group of devices and the intermediate group of devices. That is, the second group comprises devices(s)  106  which are common and known by both the sender device and the receiver device, or in other words, devices with which both the sender device  102  and the receiver device  104  have previously established a connection. That is, the second group may be represented by an empty set if the sender device  102  and the receiver device  104  have no common communication devices to which they both have previously established a communication. The identification of the second group is then received by the sender device  102 . 
     In a case there exists at least one common device, hereinafter denoted as a third device  106 , in the first group and said second group of devices, the establishment of a communication between the sender device and the receiver continues as follows. The sender device  102  requests a reference from at least one of the common third device(s)  106  regarding the receiver device  104 . 
     References have briefly been discussed above. A reference may be based on a Hash value. Hash values per se are known in the art and will thus not be further described in this disclosure. The reference may also be based on a set of statements, wherein the statements may inter alia pertain to contact information, such as a name and/or an address, of a user of the device of which the reference is associated with. For example, if the reference is associated with the receiver device  104  the reference may comprise a name and/or an address of the receiver device  104  and/or a user of the receiver device  104 . The reference may be comprised in an XML document. 
     Further, a reference may be associated with a sender and a recipient. Thus, in other words a reference may be said to be signed (by a sender) towards a recipient, wherein the signature which is used to sign the reference then advantageously comprise identification of the recipient device. 
     Optionally, when the reference is transmitted from a first device to a second device, for example from the receiver device  104  to the sender device  102 , the reference may be encrypted, which may have the general effect of increasing confidentiality and security of the transmission, and in particular increasing confidentiality and security of the transmission of the reference. 
     The sender device  102  requests a reference of the receiver device  104  from the third device  106 , wherein the reference sent from the third device  106  is addressed to and associated with the sender device  102 , and wherein the sent message comprising the reference may be encrypted by the third device  106  such that only the sender device  102  may decrypt the message part comprising the reference. The sender device  102  may for example request information pertaining to identification of the receiver device  104  as performed by the third device  106 . 
     That is, the third device  106  may perform identification of the receiver device  104  by comparing references or reference values. The reference values may be Hash values. The reference values may alternative be sequence numbers. The reference may alternative be identity information received from the sender device. The references or reference values may be a combination of Hash values, sequence numbers and identity information. 
     The third device  106  may thus be viewed as a trusted third part. The information pertaining to identification of the receiver device  104  may be associated with a previously established communication between the receiver device  104  and the third device  106 . 
     When the sender device  102  receives the reference from the third device  106 , which reference has been sent from the third device  106  to the sender device  102  via the receiver device  104 , the sender device  102  may verify the reference by comparing information comprised in the reference with previously stored information associated with the third device  106 , such as a sequence number associated with previous communication between the sender device  102  and the third device  106 . If the message part comprising the reference has been encrypted by the third device  106  the sender device  102  may first need to decrypt the message. 
     The reference may also be associated with the sender device  102  by incorporating an address field in the reference and to add the identity of the sender device  102  in the address field. This adds security to the process since the sender device  102  may ensure that the information delivered to the third device  102  is associated with the sender device  102  although the request is sent from the sender device  102  to the receiver device  104  and not from the sender device  102  directly to the third device  106 . That is, the reference request is received by the receiver device  104 , which receiver device  104  then forwards the reference request to the third device  106 . The third device  106  thus receives the reference request regarding the receiver device  104  from the receiver device  104 . The third device  106  then sends the reference to the receiver device  104 . The receiver device  106  thus receives the reference and sends the reference to the sender device  102 , which receives and verifies the reference. 
     The sender device  102  may then create a first public encryption key for establishing communication from the sender device  102  to the receiver device  104 . 
     The sender device  102  then encrypts the received reference with the created first public encryption key. Further, the sender device  102  encrypts the created first public encryption key using an additional public encryption key, wherein the additional public encryption key is associated with the previously established communication between the sender device  102  and the third device  106 . The encrypted first public encryption key and the encrypted received reference are then sent from the sender device  102  to the receiver device  104 . The receiver device  104  thus has no knowledge of the first public encryption key as created by the sender device  102 . In addition the receiver device  104  has no knowledge of the additional public encryption key associated with the previously established communication between the sender device  102  and the third device  106 . Hence the receiver device  104  is neither able to decrypt the encrypted first public encryption key nor the encrypted received reference. 
     In order for the receiver device  104  to validate the information pertaining to the previously established communication between the receiver device  104  and the third device  106  comprised in the encrypted reference the receiver device  104  forwards the encrypted first public encryption key to the third device  106 . This message sent from the receiver device  104  to the third device  106  further comprises a request pertaining to decryption of the encrypted first public encryption key. Since the first public encryption key has been encrypted with the additional public encryption key which, as stated above, is associated with the previously established communication between the sender device  102  and the third device  106 , the third device  106  is able to decrypt the encrypted first public encryption key. The decrypted first public encryption key can then be sent back from the third device  106  to the receiver device  104 . For added security the third device  106  may encrypt the decrypted first public encryption key using a further public encryption key using an additional public encryption key, wherein the additional public encryption key is associated with the previously established communication between the third device  106  and the receiver device  104 . 
     Since the receiver device  104  knows the further public encryption key which has been used to encrypt the first public encryption key the receiver device  104  may thus decrypt the, received encrypted first public encryption key after reception. 
     Using the decrypted first public encryption key the receiver device  104  may thus decrypt the previously received encrypted reference pertaining to the previously established communication between the receiver device  104  and the third device  106 . The receiver device  104  may then validate the contents of the reference. That is, by comparing information comprised in the reference to information, such as sequence numbers, comprised in the receiver device  104 , the receiver device  104  is able to verify that information comprised in reference is correct and indeed pertains to the previously established communication between the receiver device  104  and the third device  106 . 
     If the reference comprises a Hash value (as described above) the receiver device  104  may calculate the Hash value of the first public encryption key. The receiver device  104  may then perform a comparison between this calculated Hash value and the Hash value comprised in the reference in order to verify that the reference has not been altered during the transmission from the third device  106  to the sender device  102  via the receiver device  104 , or from third device  106  to the receiver device  104 . 
     An established communication between a sender device  102  and a receiver device  104  may be said to define a digital contract. A digital contract may thus pertain to a digital relationship between two or more communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 , wherein the contract may comprise information pertaining to digital signatures and/or digital witnesses (as will be further disclosed below). A digital contract thus created may be utilized to identify the communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  when the communication device  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114  interacts, or communicates, with other communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 . Digital contracts may be utilized for authentication, access rights and/or for signature purposes. Digital contracts may therefore be used to retrieve references. 
       FIG. 2  shows a schematic diagram of a communications system  200  in which the invention may apply. As in the communications system  100  of  FIG. 1 , the communications system  200  comprises a number of communication devices  102 ,  104 ,  202 ,  204 ,  206 ,  208 ,  210  which may or may not be able to communicate with each other. 
     In the following it will be assumed that the system  200  is in a state of operation and that communications is to be established between a sender device  102  and a receiver device  104 , as indicated by the dashed line  224 . 
     As for the method disclosed above with reference to the communications system  100  of  FIG. 1 , a first device  102 , denoted a sender device, wishes to establish a communication with a second device  104 , denoted a receiver device, in the communications system  200 . In the exemplary scenario of  FIG. 2  the sender device  102  is associated with communication devices  202  and  208 . That is, the sender device  102  has previously established communication with communication devices  202  and  208  as indicated by the solid lines  212  and  218 . Similarly, the receiver device has previously established communication with communication devices  204 ,  206  and  210  as indicated by the solid lines  216  and  222 . 
     It may thus be concluded that the sender device  102  and the receiver device  104  according to this scenario do not share a common communication device. In the language set forth above with reference to  FIG. 1  the second group may be represented by an empty set. However, it is assumed that the sender device  102  is associated with a fourth device  202 . Further the receiver device  104  is associated with a fifth device  204 . The fourth device  202  is moreover associated with the fifth device  204  as indicated by the solid line  214 . See further the description associated with  FIG. 3  below. 
     Wherein in a case there does not exist at least one common third device in the first group and the second group of devices, the establishment of a communication between the sender device and the receiver may continue as follows. 
     The sender device  102  sends a request comprising at least an identification of at least one sub-group associated with a fourth device  202  with which sub-group the sender device  102  is associated. This request is received by the receiver device  104 . The receiver device  104  analyses the identification of the at least one sub-group comprised in the request and compares the identification to a list comprising at least one sub-group with which the receiver device  104  is associated. 
     In a case at least one common sub-group is found the receiver device  104  sends at least an identification of the at least one common sub-group associated with a fifth device  204  to the sender device  102 . The at least one common sub-group is thus associated with both the sender device  102  and the receiver device  104 . It may thus be said that the sender device  102  may be associated with the receiver device  104  via the fourth device  202  and the fifth device  204 . 
     The identification of the at least one common sub-group is then received by the sender device  102 . The sender device  102  then sends a message to the receiver device  104 , wherein the sender device  102  requests a reference from the fifth device  204  regarding said receiver  104 . The message further comprises information that the reference is to be validated by the fourth device  202 . This request is forwarded to the fifth device  204  by the receiver device  104 . After reception the fifth device  204  sends the reference to the receiver device  104  and the receiver device  104  forwards the reference to the sender device. 
     However, since it may be assumed that communication has not been established between the sender device  104  and the fifth device  204  (otherwise the sender device  102  and the receiver device  104  should have the fifth device  204  as a common device) the sender device  102  may not be able to validate the received reference. Therefore the sender device  102  sends the received reference to the fourth device  202  for validation, wherein the message sent from the sender device  102  to the receiver device  202  may also comprise information pertaining to the origin of the reference. For the present case the origin of the reference is the fifth device  204 . After reception and validation of the reference the fourth device  202  sends the validated reference to the sender device  102 . The message from the fourth device  202  to the sender device  102  may also comprise validating information pertaining to the origin of the reference. That is, for the present case the validating information pertaining to the origin of the reference would disclose the fifth device  204  as the origin. 
     The sender device  102  may then create a first public encryption key for ester establishing communication from the sender device  102  to the receiver device  104 . 
     The sender device  102  then encrypts the received reference with the created first public encryption key. Further, the sender device  102  encrypts the rested first public encryption key using an additional public encryption key, wherein the additional public encryption key is associated with the previously established communication between the sender device  102  and the fourth device  202 . The encrypted first public encryption key and the encrypted received reference are then sent from the sender device  102  to the receiver device  104 . The receiver device  104  thus has no knowledge of the first public encryption key as created by the sender device  102 . In addition the receiver device  104  has no knowledge of the additional public encryption key associated with the previously established communication between the sender device  102  and the fourth device  202 . Hence the receiver device  104  is neither able to decrypt the encrypted first public encryption key nor the encrypted received reference. 
     In order for the receiver device  104  to validate the information pertaining to the previously established communication between the receiver device  104  and the fifth device  204  comprised in the encrypted reference the receiver device  104  forwards the encrypted first public encryption key to the fifth device  204 . This message sent from the receiver device  104  to the fifth device  204  further comprises a request pertaining to decryption of the encrypted first public encryption key. 
     Since the first public encryption key has been encrypted with the additional public encryption key which, as stated above, is associated with the previously established communication between the sender device  102  and the fourth device  202 , the fifth device  204  is thus not able to decrypt the encrypted first public encryption key. In order for the encrypted first public encryption key to be decrypted the fifth device  204  thus forwards the request to the fourth device  202 , which thus is able to decrypt the encrypted first public encryption key. The decrypted first public encryption key can then be sent back from the fourth device  202  to the receiver device  104  via the fifth device  204 . For added security the fourth device  202  and the fifth device  204  may encrypt the decrypted first public encryption key using further public encryption keys. Separate encryption keys are used during transmission from the fourth device  202  to the fifth device  204  and during transmission from the fifth device  204  to the receiver device  104 . 
     Using the decrypted first public encryption key the receiver device  104  may thus decrypt the previously received encrypted reference pertaining to the previously established communication between the receiver device  104  and the fifth device  204 . The receiver device  104  may then validate the contents of the reference. That is, by comparing information comprised in the reference to information, such as sequence numbers, comprised in the receiver device  104 , the receiver device  104  is able to verify that information comprised in reference is correct and indeed pertains to the previously established communication between the receiver device  104  and the fifth device  204 . 
     If the reference comprises a Hash value (as described above) the receiver device  104  may calculate the Hash value of the first public encryption key. The receiver device  104  may then perform a comparison between this calculated Hash value and the Hash value comprised in the reference in order to verify that the reference has not been altered during transmission. 
     In a case there are no sub-groups common to both the sender device  102  and the receiver device  104 , the receiver device  104  may send a message to the sender device  102  indicating that no common sub-groups are found. The receiver device  104  may further request that the sender device  102  sends a new request comprising at least an identification of at least one sub-group with which the sender device  102  is associated, and which identification was not previously transmitted from the sender device  102  to the receiver device  104 . The receiver device  104  then receives this new request and analyses the identification as described above. The outlined procedure may continue until a common sub-group is found. Alternatively, if no common sub-group is to be found the process of establishing communications between the sender device  102  and the receiver device  104  may be terminated. Alternatively, if no common sub-group is to be found the sender device  102  and the receiver device  104  may search for a common device associated with a higher hierarchical level, as will be described below. 
       FIG. 3  shows an example of a communications system  300  in which communication has previously been established between the fourth device  202  and devices  102  and  302 , respectively, as indicated by the solid lines  308  and  310 , and wherein communication has been established between the fifth device  204  and devices  104 ,  304  and  306 , respectively, as indicated by the solid lines  318 ,  314  and  316 . Further, communications is to be established by a sender device  102  and a receiver device  104  as indicated by the dashed line  320 . Thus, devices  102 ,  202  and  302  may be said to represent a first sub-group of the communications system  300  whilst devices  104 ,  204 ,  304  and  306  may be said to represent a second sub-group of the communications system  300 . The sub-groups may also be said to represent different classes. 
     The sub-groups may for example represent different geographical locations, such as different nations or countries or parts thereof. Thus, in this case the fourth device  202  and the fifth device  204  may for example represent or, act on the behalf of, different government bodies in the respective countries associated with the fourth device  202  and the fifth device  204 , respectively. For example, the fourth device  202  may be geographically located in a first nation whilst the fifth device  204  may be geographically located in a second nation different from said first nation. Examples of suitable government bodies may include an agency responsible of handling identification information, such as a national identity register. As such the fourth device  202  and the fifth device  204  may be said to represent so called trusted third parties. 
     The government bodies in different countries may be associated with an organization, such as a global trust center, which organization may enforce or suggest communication conditions which should be fulfilled by communication devices for the communication devices to be able to establish communication with each other. The organization may thus communicate these communication conditions to the above disclosed master devices. Moreover, it may be required that the organization certifies the master devices. 
     In a case the communications system  300  is associated with a corporate company the different sub-groups may represent different departments or divisions within the corporate company. Thus, in this case the fourth device  202  and the fifth device  204  (which are associated as indicated by the solid line  312 ) may for example represent different data service centers associated with each department or division associated with the fourth device  202  and the fifth device  204 , respectively. Other examples include, but are not limited to, different Internet service providers, Internet communities, bank memberships, dub memberships, and the like. It is generally a requirement and/or an agreement that the sender device  102  and the receiver device  104  trusts the authority, agency, company, or the like (represented by the fourth device  202  and the fifth device  204 ) offering and/or being responsible of the Internet service, Internet community, bank membership, or club membership. Again, the fourth device  202  and the fifth device  204  may be said to represent so called trusted third parties. As will be appreciated by the skilled person these are just a few examples in which the invention may apply. 
     In general, it may thus be assumed that at least one device in each sub-group (here exemplified by the fourth device  202  in the first sub-group and the fifth device  204  in the second sub-group, respectively) has established communication with a device in another sub-group. Further, in some case it may be assumed that one of the sub-group devices (such as the fourth device  202  in the first sub-group and the fifth device  204  in the second sub-group, respectively) acts as a government body which may be responsible for issuing memberships to each device in the sub-group. 
     In addition, a communication device may be associated with a plurality of different sub-groups, wherein each associated sub-group pertains to different applications. For example, on the one hand a communication device may be associated with a bank membership, and on the other hand the communication device may simultaneously be associated with Internet community. 
       FIG. 4  shows a schematic diagram of a communications system  400 , similar to the communications system  300  of  FIG. 3  in which the invention may be applied. As in  FIG. 3  the sender device  102  wishes to establish communications to the receiver device  104  as indicated by the dash-dotted line  422 , wherein the sender device  102  is associated with a first sub-group via the fourth device  202  and the receiver device  104  is associated with a second sub-group via the fifth device  204  as indicated by solid lines. According to the scenario as disclosed in  FIG. 4  the first sub-group comprises devices  102 ,  202  and  412 , whereas the second sub-group comprises devices  104 ,  204  and  420 . With reference to the above the first and second sub-groups may represent different countries. For example the first sub-group may represent devices in a first country and the second sub-group may represent devices in a second country. The fourth device  202  and the fifth device  204  may then act as government bodies. 
     In this example the sender device  102  is further associated with a third sub-group comprising devices  102 ,  406 ,  408  and  410  as indicated by dashed lines and with a fourth sub-group comprising devices  102 ,  414 ,  416  and  418  as indicated by dotted lines. For example the third sub-group may represent devices associated with the same bank, whereas the fourth sub-group may represent devices associated with the same Internet service provider. 
       FIG. 5  shows a schematic diagram of a communications system  500 , similar to the communications system  100  of  FIG. 1  in which the invention may apply. As in the communications system  100  of  FIG. 1 , the communications system  200  comprises a number of communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  502 ,  504  which may or may not be able to communicate with each other. 
     In the following it will be assumed that the system  500  is in a state of operation. 
     As for the method disclosed above with reference to the communications system  100  of  FIG. 1 , a first device  102 , denoted a sender device, wishes to establish a communication with a second device  104 , denoted a receiver device, in the communications system  500 . As in  FIG. 1  solid lines  510 ,  512 ,  514 ,  516 ,  518 ,  520 ,  522 ,  524 ,  526  between two communication devices  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  502 ,  504  represents that communication has previously been established between the two communication devices at each end of the solid line  510 ,  512 ,  514 ,  516 ,  518 ,  520 ,  522 ,  524 ,  526 . That is, as in the exemplary scenario of  FIG. 500  communication has previously been established e.g. between the sender device  102  and the third device  106 , between the sender device  102  and a first auxiliary device  502 , between the receiver device  104  and the third device  106 , and between the receiver device  104  and a second auxiliary device  504 . As indicated by the dashed line  528  communications is to be established between the sender device  102  and the receiver device  104 . 
     The first and second auxiliary devices  502 ,  504 , respectively, may be said to represent digital witnesses for the sender device  102  and the receiver device  104 , respectively. That is, it may be required that all relations established involving the sender device  102  are monitored by the first auxiliary device  502 . More generally, it may thus be required that all relations are monitored by auxiliary devices; a first auxiliary device  502  monitors the operations of, and/or the messages sent and received by, the sender device  102 , whilst a second auxiliary device  504  monitors the operations of, and/or the messages sent and received by, the receiver device  102 . The monitoring process of the first and second auxiliary devices  502 ,  504  may thus be said to involve capturing message transaction information, such as the sender and/or recipient of the message. The monitoring process of the first and second auxiliary devices  502 ,  504  may also comprise supplying the transmitted messages with a time stamp and/or a digital signature. Time stamps and digital signatures per se are known in the art and will thus not be further discussed in this disclosure. When establishing communication between a sender device  102  and a receiver device  104  the first auxiliary device  502  of the sender device  102  and the second auxiliary device  504  of the receiver device  204  may also be required to establish communication. 
     Next, with reference to the communications system  500  of  FIG. 5  the process of terminating established communication between the sender device  102  and the receiver device  104  will be disclosed. However the process applies also to the communications systems  100 ,  200 ,  300  and  400  of  FIGS. 1-4 , mutatis mutandis. 
     Firstly, it is to be understood that in a case the first auxiliary device  502  monitors the operations of, and/or the messages sent and received by, the sender device  102 , the messages sent by the sender device  102  comprise two digital signatures; one digital signature associated with the sender device  102  and one digital signature associated with the first auxiliary device  502 . 
     Thus in a case the first auxiliary device  502  monitors all communications relations established by the sender device  102  the sender device  102  may terminate the established communication between the sender device  102  and the receiver device  104  by sending a message to the first auxiliary device  502 , wherein the message comprises information stating that the first auxiliary device  502  shall not insert a digital signature into the monitored message. That is, in this case the messages sent by the sender device  102  comprise one digital signature, which digital signature is associated with the sender device  102 . If the receiver device  104  receives a message not comprising a digital signature of the first auxiliary device  502  the receiver device  502  may choose to classify the received message as incomplete and may thus further ignore its contents. Since the receiver device  104  ignore the contents of the received message the established communication from the sender device  102  to the receiver device  104 , and/or the established communication between the sender device  102  and the receiver device  104  may be said to have been terminated. Alternatively, the receiver device  104  may send a message to the sender device  102  stating that the received messages was interpreted as incomplete since the received message did not comprise a digital signature of the first auxiliary device  502 . 
     A method in a communications system  100 ,  200 ,  300 ,  400 ,  500  for authentication of a sender device  102  and a receiver device  104 , wherein the method has been disclosed above with references to  FIGS. 1-5 , can also be illustrated in a flowchart. Thus such a method may be summarized as comprising creating, in a step  602 , by the sender device  102 , an identification of the sender device  102 ; creating, in a step  604 , by the receiver device  104 , an identification of the receiver device  104 ; sending, in a step  606 , by the sender device  102 , a request pertaining to establishing a relation between the sender device  102  and a receiver device to the receiver device  104 ; sending, in a step  608 , by the receiver device  104 , at least an identification of a second master device  154  to the sender device  102 ; sending, in a step  610 , by the sender device  102 , the identification of the second master device  154  to a first master device  152 ; sending, in a step  612 , from the first master device  152 , a request pertaining to communication conditions needed by the sender device  102  for the sender device  102  to establish communication with the receiver device  104  to the second master device  154 ; sending, in a step  614 , from the second master device  154 , the communication conditions to the first master device  152 ; if it is determined, in a step  616 , that the sender device  102  fulfills the communication conditions, providing, in a step  618 , by the sender device  102 , a first access key to the first master device  152 ; and providing, in a step  620 , by the receiver device  104 , a second access key to the second master device  154 . 
     It should here be noted that a system and method for establishing communications from a sender device  102  to a receiver device  104  has been disclosed. However, as the skilled person will understand, communications from the receiver device  104  to the sender device  102  may be established in the same way since, as stated above, the sender device  102  may also comprise the functionality of the receiver device  104  and vice versa. Thus the sender device  102  may interchangeably act as a receiver device  104  and vice versa. Thus it may be said that the above system and method may be applied for establishing communications between the sender device  102  and the receiver device  104 . 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.