HK1183992A1 - Mobile handset identification and communication authentication - Google Patents

Description

Identification and communication authentication of mobile handheld devices

Technical Field

The present invention relates to the identification and authentication of mobile handsets and to securing the communication channel between a mobile handset and an application server. In particular, the present invention relates to systems and methods for authenticating and securing an online communication channel between a mobile handset and an online application server in a manner that allows the application server to verify the identity of the mobile handset (and vice versa).

Background

In modern commerce, more and more transactions are conducted electronically via online application servers by means of communications over a network (e.g., the most common internet). While traditionally conducted by personal computers and other devices that typically have significant processing power, transactions are increasingly being conducted by networked mobile phones and other mobile handsets that do not necessarily have the same processing power.

In the remainder of this description, the term "mobile handset" should be interpreted to include any mobile communication device capable of communicating over a communication network (e.g., a cellular mobile network) and having at least a limited amount of processing capability. The term should be interpreted to specifically include all mobile or cellular telephones but may also include portable computers such as notebook computers, palm top personal computers, etc.

However, a problem with using traditional online transactions is the inherent security risks associated with online communications. Illegal operators continue to develop new techniques to intercept user and transaction information and utilize this information to defraud participants. Examples of such security threats include identity theft, man-in-the-middle (MITM) attacks, pharming, phishing, over-the-air SMS/data sniffing, third party infrastructure hijacking, trojans, keyloggers, and combinations of these threats.

To make online transactions more secure, a variety of security techniques have been developed. One such technique, one example of which is known as two-factor authentication, utilizes a user's mobile phone as a device for an off-line transaction to provide an additional layer of security. Since it is assumed that there is a one-to-one relationship between the user and his or her mobile phone, in order to use this technique, it is assumed that the user always holds the phone. Short Message Service (SMS) messages are currently the preferred delivery mechanism for secure messages and are typically sent in the form of text messages by a service provider (e.g., a financial institution) to a user's mobile phone. The message typically includes a separate, unique one-time personal identification number (OTP) which the user must then manually enter into the secure environment that he or she wishes to access, or along with his or her normal login details before conducting the secure transaction.

Although this technique adds an extra layer of security, it is still susceptible to abuse, as SMS messages can be intercepted by techniques such as SIM card duplication, for example. This technique still requires the user to enter an 8-digit (or longer) password from the handset into the website or other secure transaction it wishes to conduct. Another disadvantage of this technique is that the cost involved with the institution hosting the secure transaction is relatively high, since the institution must send an SMS message through the GSM network provider each time the user needs to be authenticated. During any particular session, multiple authentications may occur and each such message will typically be billed separately by the GSM network provider.

Essentially, this type of two-factor authentication is not completely "out-of-band" in the true sense. Although the OTP may arrive "out-of-band" on the user's phone, the user must again enter it and transmit it on the same communications band, thus making the OPT easy to intercept again. If the browser or other communication channel being used has been compromised, the transmission of the OTP will likewise be compromised.

Another major drawback of this technology has only become apparent as mobile handheld devices are increasingly being used as devices for browsing the internet and for online transactions. The large number of mobile handsets does not allow the user to have multiple running applications at the same time. Thus, when a user is browsing the internet on a handheld device through a web browser application, he or she cannot receive an SMS with an OTP. This requires the user to turn off the browser before reading the SMS and OTP, and then to restart the browser to enter the OPT in the web site. Even where there may be multiple active applications at a given time, switching between applications may be difficult and inconvenient.

In addition to the above, most security protocols that have been developed require a significant amount of processing power to be feasible. One of the most common security measures used today in online transactions is Transport Layer Security (TLS) or its predecessor, Secure Sockets Layer (SSL). Both TLS and SSL are known as cryptographic protocols and are used to encrypt segments of a network connection at the application layer to ensure secure end-to-end transport at the transport layer. However, SSL is problematic for mobile handsets for a variety of reasons, one of which is the phenomenon that handsets typically do not have the processing power to compute their own private and public encryption key pairs that can be used for secure communications. In addition to the mobile handset in some cases possibly not being able to request a certificate, in other cases the process is still complex and tedious. Furthermore, most mobile handsets do not have enough root certificates at all, which are pre-installed on the mobile handset to enable the mobile handset to accept any regular subset of certificates issued by a conventional Certificate Authority (CAs).

Due to the above limitations and difficulties of employing mobile handsets, operators of online application servers (e.g., banks) often choose to avoid complications by drastically limiting the number and scope of online transactions that can be conducted from a user's mobile handset. This greatly inhibits the use of technology, as the user still has to access the personal computer to take advantage of the full hosting service provided by most online application servers.

Disclosure of Invention

According to the present invention there is provided a system for authenticating a communication channel between a mobile handset associated with a user and an application server, for uniquely identifying the mobile handset and for encrypting communications between the user and the application server over the communication channel, the system comprising a certificate authority, a client software application installed on the mobile handset, and a server software application installed on the application server, the system being characterised in that the system comprises a certificate authority, a client software application installed on the mobile handset, and a server software application installed on the application server

The client software application utilizes a client cryptographic module provided by the certificate authority and is configured to request a digital user certificate from the certificate authority, preferably automatically, whenever the client cryptographic module verifies that the mobile handset does not have a valid user certificate (e.g., when the mobile handset first attempts to transact with the application server);

the certificate authority is adapted to create and issue user certificates to the mobile handset upon receipt of the request, the user certificates comprising at least one identifier uniquely associated with the mobile handset;

the server side software application utilizing a server side encryption module provided by the certificate authority and configured to request and receive a user certificate from the mobile handset, to verify with the server side encryption module that the user certificate originated from the certificate authority, to uniquely identify the mobile handset based on an identifier in the user certificate, and to transmit to the mobile handset a digital server certificate issued by the certificate authority to the server side software application, where the digital server certificate is received by the client side software application and verifies with the client side encryption module that the digital server certificate originated from the certificate authority; wherein

Upon successful authentication of the user credentials by the server-side software application and successful authentication of the server credentials by the user-side software application, the user-side software application and the server-side software application are further configured to share encryption keys (more specifically, public and private key pairs associated with the respective credentials) with their respective credentials to provide encryption that is useful for further data encryption between the mobile handset and the application server.

The invention is further characterized by specifying the digital user certificate and the digital server certificate as X.509 certificates; specifying the identifier as a unique digital key issued by a certification authority and assigned to the mobile handset; providing the server certificate to include a server identifier uniquely associated with the application server and by which the mobile handset can uniquely identify the application server; and specifying the user and server certificates as including certificate authority signatures generated using the certificate authority private key, corresponding certificate authority public keys, by which the signatures can be verified as being known to both the user-side and server-side cryptographic modules and/or software applications.

The invention is further characterized by specifying the client-side and server-side encryption modules as integrated modules provided by a certificate authority that contains the functionality of both the client and server; and the user and server side encryption modules are specified to be compiled into user side and server side software applications, respectively, to provide additional encryption functionality.

The invention is still further characterized by the provision that the certificate authority is further configured to calculate a user private and public key pair for the mobile handset when issuing the user certificate to the mobile handset; securing the communication channel between the certificate authority and the mobile handset by Diffie-Hellman key exchange or similar protocol; transmitting the user private key to the mobile handset if the Diffie-Hellman key exchange is successful; and a user public key included in the user certificate; alternatively, it is provided that the client software application or encryption module is further configured to instruct the mobile handset to calculate the user private and public encryption key pairs itself.

It is a further feature of the present invention to provide that the server side software application or encryption module is configured to instruct the application server to compute a server private and public key pair; instead, a certificate authority is provisioned to compute server private and public key pairs for itself; specifying the application server public key as being included in the server certificate; providing for the client-side and server-side software applications or encryption modules to be configured to share an encryption key by asymmetrically encrypting their communications using their respective public and private key pairs; and specifying the encryption key as a symmetric encryption key.

A further feature of the present invention provides for the client software application or encryption module to be further configured to instruct the mobile handset to store the received user credentials and user private and public key pairs in a secure (preferably encrypted) location in the mobile handset memory from which the user credentials and user private and public key pairs can only be retrieved by authorized applications (preferably only the client software application and/or encryption module).

Still further features of the invention provide for the certificate authority to periodically and automatically issue new certificates to the mobile handset and/or application server; defining the new user certificate as comprising a new user private and public key pair; and to provide for new certificates to be issued once a year.

A further feature of the present invention is to provide that the client software application or encryption module verifies (as the case may be) that it is indeed in communication with the certificate authority when requesting the user certificate, the verification being performed by the client software application or encryption module verifying the certificate authority digital certificate against the certificate authority digital certificate of the client software application or encryption module assigned as part, and instead (as the case may be) that the verification is performed by the client software application or encryption module simply encrypting communications with the certificate authority using the certificate authority public key, the verification being successful if the certificate authority is able to decrypt the communications using the certificate authority private key.

The present invention further provides a method for authenticating a communication channel between a mobile handset associated with a user and an application server, for uniquely identifying the mobile handset, and for encrypting communications between the mobile handset and the application server over the communication channel, the method being for use at the application server and comprising the steps of

Receiving a digital user certificate from the mobile handset by a server-side software application installed on the application server and verifying the certificate by utilizing functionality provided by an encryption module assigned by a certificate authority, the digital user certificate having been issued to the mobile handset by the certificate authority and comprising at least one identifier uniquely associated with the mobile handset;

transmitting a digital server certificate from the application server to the mobile handset to authenticate the application server, the authentication of the application server being performed by a client software application installed on the mobile handset using the functionality provided by the client encryption module provided by the certificate authority, the digital server certificate having been issued to the application server by the certificate authority;

if the authentication of both the mobile handset and the application server is successful, sharing an encryption key with the mobile handset using the encryption provided by the user and server credentials; and

data communicated to and from the mobile handset is encrypted by the encryption key.

A further feature of the present invention provides for the sharing of the encryption key to include sharing a symmetric encryption key.

The present invention still further provides a method of enabling authentication of a communication channel between a mobile handset associated with a user and an application server and unique identification of the mobile handset by the application server, the method being performed at a certificate authority and comprising the steps of

Receiving a request for digital user credentials from a mobile handset, the request having been sent from a client software application installed on the mobile handset;

issuing a user certificate to the mobile handset, the user certificate including at least one identifier uniquely associated with the mobile handset and by which the mobile handset is uniquely identifiable;

issuing a digital server certificate to an application server;

a digital signature included in both the user certificate and the server certificate, the digital signature enabling the user-side software application and the server-side software application to exchange certificates and verify the respective certificates by using at least the digital signature and the encryption module provided by the certificate authority.

A further feature of the present invention provides for the method to include the steps of: computing a unique asymmetric key pair comprising a user public and private key; upon receipt of the request, securing the communication channel with the mobile handset by Diffie-Hellman or similar key exchange; transmitting at least the user private key to the mobile handset over the secure communication channel; a user public key included in the user certificate; and periodically re-issuing new digital user credentials, possibly including new user private and public key pairs, to the mobile handset and/or the application server.

Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram of an authentication system according to the present invention; and

fig. 2 is a schematic layout of a digital certificate according to the present invention.

Detailed Description

Fig. 1 shows a system 1 for authenticating a communication channel 3 between a mobile handset 5 (in this example a mobile phone) associated with a user 7 and an application server 9. The system 1 comprises a certificate authority 11, as well as a client side software application 13 installed on the mobile phone 5 and a server side software application 15 installed on the application server 9. In addition, the mobile telephone 5 and the application server 9 each include an encryption module (not shown) provided by a certificate authority 11, the certificate authority 11 providing encryption functionality for the user and server side applications 13, 15. It should be apparent that the encryption modules may be compiled as part of the server and client software applications, respectively. Reference is made in the remainder of this description to the functionality of the server-side or client-side software application, it being understood that such functionality may in fact be provided by the server-side or client-side encryption module, and vice versa.

The first time the client software application requests encryption or unique user identification, it is determined that no digital user certificate 17 is currently installed on the mobile telephone 5. At this point, the application automatically connects to the online server of the certificate authority 11 ("CA") and attempts to request a digital user certificate 17 from the server 11. The client application 13 first verifies that the server with which it is communicating is indeed the CA11, and not a rogue server. This is done by verifying the CA certificate signature 21 sent by the CA11 to the mobile phone 5 against the CA certificate 23 of the client software application 13 or encryption module assigned as part. However, it should be apparent that the authentication of the CA may be inherent if the user side software application is able to decrypt the communication from the CA encrypted with the CA private key. If the client software application is able to decrypt the CA that encrypted the CA communication by using the CA public key, it is known that the CA is what it purports to be.

Upon successful authentication of the CA server 11, the CA generates and issues a digital user certificate 17 to the mobile telephone. User certificate 17 is a signed x.509 digital certificate that can be used first to identify the mobile handset 5 at which the certificate is installed and also to share a symmetric encryption key 25 with the application server 9. The symmetric encryption key, in turn, may be used for data encryption between the handheld device 5 and the application server 9. This feature will be described in more detail below. Signing the certificate 17 with the private key 27 associated with CA11, the corresponding public key 29 of CA11 is known to both user-side and server-side software applications or to the encryption module (as the case may be) so that they can decrypt the signature and verify that it is signed by the CA private key 27 and therefore authentic.

When issuing the signed digital user certificate 17 to the handheld device 5, the server 11 computes a user private 31 and public 33 encryption key pair for the handheld device 5. This occurs primarily if the handheld device 5 does not have sufficient processing power to compute the key pair itself. The server 11 then attempts to establish a secure communication channel between the server 11 and the handset 5 by means of a Diffie-hellman (dh) key exchange or similar protocol. If the DH key exchange is successful, the server 11 sends the user private key 31 to the handheld device 5 over a secure channel, where the user private key 31 is received by the user side software application 13 at the handheld device 5. The associated user public key 33 may then be included in the user certificate 17 and separately transmitted to the handheld device 5. After receiving the user key pair and certificate 17, the client software application 13 stores them in the encrypted (sandboxed) portion of the memory of the handheld device 5 from which only authorized applications (including the client software application 13 and/or the client encryption module) can access the user key pair and certificate 17.

It will be appreciated that if the handheld device 5 has sufficient processing power, it is able to calculate the user key pair 31, 33 itself. In this case, the user private key 31 does not need to be transferred between the server 11 and the handheld device 5 and can still be hidden in the memory of the handheld device. Thus, the user side software application 13 can simply transmit the user public key 33 to the application server 11 along with a request for the digital user certificate 17. The server 11 then signs the user's public key 33 included in the certificate 17 with its own private key 27 as before.

Figure 2 shows a typical layout of a digital user certificate 17. In addition to the user public key 33 and the CA signature 35, the certificate contains an identifier 37, which identifier 37 is a unique association with the mobile handset 5. The identifier 37 may be any unique key issued by the CA. In the current embodiment of the invention, identifier 37 is a serial number generated by CA 11. It will be appreciated that due to the continuity of the identifier 37, there is a one-to-one relationship between each certificate issued by the CA11 and the mobile handset. In addition to the above, the certificate 17 may also include other information, such as the mobile handset number 39 associated with the SIM card of the handset 5, the IMEI41 and/or IMSI43 number of the handset, and the certificate validity period 44.

It should be appreciated that in the above example, the issuance and storage of user credentials 17 may occur entirely in the background and automatically, without any user intervention. Once the digital user certificate 17 has been issued by the CA11 and stored in a secure location on the mobile handset 5, the digital user certificate 17 may be used by the user side software application 13 and/or encryption module to identify the handset 5, authenticate the communication channel between the handset 5 and the application server 9, and encrypt communications between the handset 5 and the application server 9.

The application server 9 also has a digital server certificate 45 issued by the CA 11. The issuance of the server certificate 45 may occur at any time, but typically at the time of the request from the application server 9. Typically, when the application 15 is first installed on the application server 9, the request will also come directly from the server side software application 15 or server side encryption module. The format of the server certificate 45 is similar to that of the user certificate 17 described with reference to figure 2 and includes its own server public key 47. The corresponding server private key 49 is held in a secure location on the server 9, from which it is only accessible through the server 9. Unlike the case of the user key pair 31, 33, the server key pair 47, 49 is typically computed by the server 9 itself, which server 9 typically has sufficient processing power to do so. Thus, when requesting a server certificate 45 from CA11, the server 9 sends its public key 47 to CA11, which in turn, CA11 will issue the server certificate 45 including the server public key 47 and sign the server certificate 45 with its private key 27.

If both the handset 5 and the application server 9 have issued digital certificates, the certificates 17, 45 may be used to authenticate the communication channel between the handset 5 and the application server 9, to identify the handset and/or the application server and to encrypt the communication between the handset 5 and the application server 9. Whenever the mobile handset 5 connects to the application server 9, the handset 5 will start a certificate exchange procedure whereby the certificate 17 of the handset 5 is sent to the server 9 and the certificate 45 of the server is sent to the handset 5. The two parties will then verify the content of the received certificate 17, 45 and the digital signature to ensure that the details in the certificate 17, 45 have not been tampered with. The authentication is done by using the CA digital certificates 51 or their respective encryption modules of the client side application 13 and the server side application 15 as part. However, knowledge of the CA public key 29 may be sufficient to enable verification of the respective certificate. It should be understood that the CA digital certificate 51 will include the CA public key 29, and the client-side and server-side applications will therefore use the CA public key 29 to decrypt the signed certificate 17, 45. If the certificates cannot be decrypted with the CA public key 29, it is clear that they are not signed with the CA private key 27 and are therefore not trusted.

At this point, both parties can determine that they are talking to the intended recipient. The handheld device 5 and the server 9 are now able to share the encryption key 25 in such a way that further encryption of their communication can be done. The shared encryption key 25 is typically a symmetric encryption key. It will be appreciated that after the certificate exchange, the handset 5 will possess the application server public key 47 and the application server 9 will possess the handset public key 33. Thus, the encryption key may be encrypted by the handset using the server public key 47 and by the server using the handset public key 33, thereby ensuring that only the recipients are able to decrypt communications using their respective private keys 31, 49.

The handheld device identifier 37 included in the user certificate 17 may also be used by the application server 9 to uniquely identify the handheld device 5 and, accordingly, the user 7. The application server may have a database of all identifiers issued by the CA11 to the application server client and may choose to communicate only with the handheld devices included in the database. The identifier 37 may also be associated to other information about the user 7 by the application server 9. Thus, when the application server 9 receives the user certificate 17 from the handheld device 5, the application server 9 is able to verify firstly that the certificate is authentic and issued by the CA11, and secondly that the handheld device 5 is in fact associated with a registered user. Thus, the digital user certificate 17 is used not only to authenticate the communication channel 3 between the handheld device 5 and the application server 9, but also to uniquely identify the handheld device 5 attempting a transaction with the application server 9. In this way, the application server 9 can trust communications received from the handheld device and can be confident that communications over the communication channel 3 are secure.

It should be appreciated that the client software application can also verify that the application server is the legitimate owner of the certificate it sends simply by virtue of the fact that the client software application is able to decrypt communications sent to it by the application server and has been encrypted by the application server private key. Only communications encrypted with the application server private key can be decrypted with the application server public key.

In an alternative embodiment, the mobile handset and the application server may include additional, customized software modules that are distributed by the owner of the application server. In this embodiment, the customized software modules would communicate with the client-side and server-side software applications and/or the client-side and server-side encryption modules to invoke the functionality of the present invention.

It is envisioned that the CA may periodically issue new certificates to all handsets and/or application servers that it has previously issued certificates. This can be done as often as desired, but is preferably on an annual basis. Thus where the CA computes a new user private/public key pair for the mobile handset, the issuance of a new user certificate may also include the computation and issuance of a new user private/public key pair.

It is also foreseen that the system will be able to issue certificates comprising keys with larger and larger bit lengths. At the time of writing, the industry standard for public and private keys is 1024 bits. However, the system can be readily adapted to issue key pairs of 2048, 3072 and more bits.

The first time the CA receives a request for a user certificate from a new handheld device, it is understood that the CA may issue a self-signed certificate to this handheld device. The CA may then propagate the request for the certificate to the application server along with the claimed identity of the new handset, which in turn may decide whether a legitimate user certificate may be issued to the handset. If the application server decides that a legitimate user certificate should be issued to the handset, the application server propagates that decision to the CA, which in turn issues a legitimate, fully signed user certificate to the handset as described previously. In this way, the application server can maintain a record of the identity and the number of legitimate certificates issued to its user by the CA.

The above description is by way of example only and it should be understood that various modifications may be made to the described embodiments without departing from the scope of the invention. In particular, the described system architecture and data flow may be performed in many different ways and in any order that is practicable.

The system and method of the present invention provides a way to authenticate the communication channel between a mobile handset, in particular a cellular telephone, and an online application server, and a way to uniquely identify the handset performing the transaction and further encrypt the communication between the application server and the handset.

The present invention thus provides a secure way for mobile phones to transact with online application servers, so that service providers (e.g., banks) can allow and secure full-function use of their online services from mobile phones and other mobile handsets.

The system of the present invention may also be used with other mobile communication devices (e.g., notebook computers). With standard SSL technology used in most cases, a user's laptop computer is typically not issued its own digital certificate. Thus, there is typically no confirmation from the user end that the transacting user is actually who he or she claims to be. The present invention thus provides a stronger form of authentication and more secure communications than currently available systems provide. The cryptographic module provided by the CA according to the present invention enables currently available software applications to utilize the present invention.

Claims (15)

1. A system (1) for authenticating a communication channel (3) between a mobile handset (5) associated with a user (7) and an application server (9), for uniquely identifying the mobile handset (5) and for encrypting communications between the mobile handset (5) and the application server (9) over the communication channel, the system comprising a certificate authority (11), a client software application (13) installed on the mobile handset (5), and a server-side software application (15) installed on the application server (9), the system being characterized by

Said client software application (13) utilizing a client cryptographic module provided by said certificate authority (11) and configured to request a digital user certificate (17) from said certificate authority (11);

-said certificate authority (11) being adapted to create and issue said user certificate (17) to said mobile handset (5) upon receipt of said request, said user certificate (17) comprising at least one identifier uniquely associated with said mobile handset (5);

said server side software application (15) utilizing a server side encryption module provided by said certificate authority (11) and being configured to request and receive said user certificate (17) from said mobile handset (5), to verify with the server-side cryptographic module (15) that the user certificate (17) originated from the certificate authority (11), uniquely identifying the mobile handset (5) according to the identifier in the user certificate (17), and transmitting a digital server certificate (45) issued by the certificate authority (11) to the server side software application (15) to the mobile handset (5), -said digital server certificate (45) is received by said client software application (13) at said mobile handset (5) and said client cryptographic module is used to verify that said digital server certificate (45) originated from said certificate authority (11); and

upon successful verification of the user certificate (17) by the server side software application (15) and the server certificate (45) by the client side software application (13), the client side software application (13) and the server side software application (15) are further configured to share an encryption key with their respective certificates to provide encryption, the encryption key being useful for further data encryption between the mobile handset (5) and the application server (9).

2. The system (1) according to claim 1, wherein said client software application (13) automatically requests said digital user certificate (17) from said certificate authority (11) when said mobile handset (5) first attempts to transact with said application server (9).

3. The system (1) according to claim 1 or claim 2, wherein the client side software application (13) and the server side software application (15) are further configured to share an encryption key with a public and private key pair (31, 33; 47, 49) associated with their respective certificates.

4. The system (1) according to any one of the preceding claims, wherein the identifier is a unique digital key issued by the certificate authority (11) and assigned to the mobile handset.

5. The system (1) according to any one of the preceding claims, wherein the server certificate (45) comprises a server identifier uniquely associated with the application server (9) and by means of which the mobile handset (5) is able to uniquely identify the application server (9).

6. The system (1) according to any one of the preceding claims, wherein the user and server certificates (17, 45) comprise a certificate authority signature generated with a certificate authority private key, a corresponding certificate authority public key (29), by means of which certificate authority public key (29) it can be verified that the signature is known to the user-side and server-side cryptographic modules and/or software applications (13, 15).

7. The system (1) according to any one of the preceding claims, wherein the certificate authority (11) is further configured to calculate a user private and public key pair (31, 33) for the mobile handset (5) and to transmit the key pair (31, 33) to the mobile handset (5) over a secure communication channel when issuing the user certificate to the mobile handset (5).

8. The system (1) according to any one of the preceding claims, wherein the certificate authority (11) comprises the user public key (33) in the user certificate (17) and the server public key (47) in the server certificate (45).

9. The system (1) according to any one of claims 1 to 8, wherein the client software application (13) or encryption module is further configured to instruct the mobile handset (5) to calculate the user private and public encryption key pair (31, 33) itself.

10. The system (1) according to any one of the preceding claims, wherein the server-side software application (15) or encryption module is configured to instruct the application server (9) to compute a server private and public key pair (49, 47).

11. The system (1) according to any one of the preceding claims, wherein the client software application (13) or encryption module is further configured to instruct the mobile handset (5) to store the received user credentials (17) and user private and public key pairs (31, 33) in a secure location in mobile handset memory from which the user credentials (17) and user private and public key pairs (31, 33) can only be retrieved by authorized applications.

12. The system (1) according to any one of the preceding claims, wherein the certificate authority (11) issues new certificates to one or both of the mobile handset (5) and the application server (9) periodically.

13. A method for authenticating a communication channel (3) between a mobile handset (5) associated with a user (7) and an application server (9), for uniquely identifying the mobile handset (5), and for encrypting communications between the mobile handset (5) and the application server (9) over the communication channel (3), the method being for use at the application server (9) and comprising the steps of

Receiving a digital user certificate (17) from the mobile handset (5) by a server side software application (15) installed on the application server (9) and verifying the certificate by utilising the functionality provided by a cryptographic module allocated by a certificate authority (11), the digital user certificate (17) having been issued to the mobile handset (5) by the certificate authority and comprising at least one identifier uniquely associated with the mobile handset (5);

-transmitting a digital server certificate (45) from the application server (9) to the mobile handset (5) to authenticate the application server (9), the authentication of the application server (9) being performed by a client software application installed on the mobile handset (5) using the functionality provided by the client encryption module provided by the certificate authority (11), the digital server certificate having been issued to the application server (9) by the certificate authority (11);

-if the authentication of both the mobile handset (5) and the application server (9) is successful, sharing an encryption key with the mobile handset (5) using the encryption provided by the user and server credentials; and

-encrypting and decrypting data propagated to and from said mobile handset (5) by means of said encryption key.

14. A method of enabling authentication of a communication channel (3) between a mobile handset (5) associated with a user (7) and an application server (9) and unique identification of the mobile handset (5) by the application server (9), the method being performed at a certificate authority (11) and comprising the steps of

Receiving a request for digital user credentials (17) from the mobile handset (5), the request having been sent from a client software application (13) installed on the mobile handset (5);

-issuing the user certificate (17) to the mobile handset (5), the user certificate (17) comprising at least one identifier uniquely associated with the mobile handset (5) and by means of which identifier the mobile handset (5) is uniquely identifiable;

-issuing a digital server certificate (45) to the application server (9); and

the digital signatures included in both the user certificate (17) and the server certificate (45) enable the user side software application (15) and the server side software application (13) to exchange certificates and verify the respective certificates (17, 45) by using at least the digital signature and encryption module provided by the certificate authority (11).

15. The method of claim 14, comprising the steps of: computing a unique asymmetric key pair comprising user public and private keys (31, 33); -upon receipt of said request, securing a communication channel (3) with said mobile handset (5) by means of an appropriate key exchange protocol; and transmitting at least the user private key to the mobile handset over a secure communication channel.