Enabling access to data

Methods, systems, apparatus and computer programs for enabling access to data by a requesting party. A plurality of sets of data are generated. A one one-way function is then used to generate a plurality of keys each associated with a respective one of the plurality of sets. Information associated with the data in a given set is used as an input to the one-way function when generating the key for that set. The keys are distributed to requesting parties. Subsequently, a requesting party may make a data access request using the received key. Upon receipt of a key, access may be enabled to the data. The requesting party may then generate validation data from information associated with at least a part of the received data and validating the received data by comparing the validation data to data derived from the received key.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to apparatus, systems and methods for enabling access to data, and in particular to enabling access to data by a plurality of requesting parties.

Description of the Related Technology

In many communications systems it is desirable to control access to data. In particular it is desirable to have a system in which different requesting parties are allowed to access certain data portions within a given block of data while being prevented from accessing other data portions. Moreover, it is desirable to allow different parties access to the same data portions of data, while not, for example, giving two parties access to all the same data portions; that is, parties are allowed overlapping, but not necessarily identical, access.

One example of a system to provide this is described in US 2005/0180573. In this example a block of data is divided into portions. Each portion of the data is then encrypted using a different portion specific key. Requesting parties are then provided with a party specific key, which can be used to derive or decrypt portion specific keys. The party specific keys are arranged such that a given party is only able to acquire portion specific keys corresponding to portions of the data to which the party is allowed access. This enables a requesting party to decrypt, and thus access, the portions of the data to which that party is allowed access.

However, this system comes with a number of drawbacks. For example, a lost key, or removal of access rights of a given requesting party, means that all portions of the data to which a given party was previously allowed access have to be re-encrypted. In addition, this system requires any computerized equipment used by the parties to be capable of decrypting the data adding overheads to the overall system.

Consequently, there is a need for an improved system for enabling access to data.

SUMMARY

In accordance with at least one embodiment, methods, devices, systems and software are provided for supporting or implementing functionality to transfer data.

This is achieved by a combination of features recited in each independent claim. Accordingly, dependent claims prescribe further detailed implementations of various embodiments.

According to a first aspect of the invention there is provided a method of enabling access to data by a requesting party, the method comprising: generating a plurality of sets of data; using a one-way function to generate a plurality of keys each associated with a respective one of the plurality of sets, wherein information associated with a said set of data is used as an input to the one-way function when generating a key associated with the set; arranging for the keys to be available for distribution to one or more requesting parties; receiving a data access request comprising a key from a said requesting party; and enabling access, by the requesting party, to data in a said set, based on the received key.

By generating the sets, and associating the set with the keys, embodiments are able to efficiently control access to the data. Should a key be compromised—that is the key becomes known to a party which is not authorized to access the data—the only changes which need to be made are to the association between the keys and the sets. For example, a new key may be generated and the compromised key may be revoked. This is more efficient than the encryption system described in the background section as no re-encryption is required.

In addition, as a consequence of using a one-way function, a third party will be unable to create valid keys to use to access the data, and thus the only source of a valid key is via distribution from the key generator. This provides improved security to the system as the distribution of the keys can be controlled and used to restrict access to the data and as the key itself provides a means to authenticate the requesting parties and thus control access to the data. This can be compared to a system where a simple pointer, such as a URL, is provided to enable access to remote data.

By using the data itself to generate the keys, the keys are able to perform two functions. First, they enable access to the data, and secondly the keys enable a receiving party to validate the retrieved data using the key. In particular, the keys can be used to detect changes (whether accidental or from an attack) to the data between the keys being generated and the data being accessed. Since the keys (once distributed) will be held by a requesting party separately from the data, this makes it harder to modify the data without being detected.

The information associated with a set of data may identify the content of the data. Alternatively, the information associated with a set of data may comprise at least a part of the content of the data.

The method may comprise using one or more salt values as inputs to the one-way function. Furthermore, the method may comprise storing a salt value used to generate a given key as data in a set accessible using the given key.

Salt values enable, for example, different keys to be generated for the same data, thus enabling different keys to be distributed to the requesting parties. While the salt values may be sent to the requesting parties with the keys, or made available for retrieval separately, in embodiment the salt values may stored with the data in a set and distributed with the data, thus enabling the requesting party to validate the data upon receipt.

The one-way function may comprise one or more of: a hash function; a cryptographic signing function; a random number generator; and a pseudo-random number generator. In embodiments, the keys may have high entropy.

Access may be enabled for a limited number of requests comprising a given key. The method may therefore comprise generating a plurality of keys associated with a given set. The method may also comprise generating a second key associated with a given set in response to receiving a request comprising a first key associated with a given set.

This reduces the effectiveness of man-in-the-middle attacks where an attacking party intercepts a request for data, and thus acquires a valid key. Once used, the key will cease to be valid, so any attempt by the attacking party to gain access to the data using the key will be unsuccessful.

The method may comprise associating a plurality of keys with a said set; arranging for the plurality of keys to be available for distribution; enabling access to the said set of data in dependence on a predetermined criterion being satisfied, said predetermined criterion being dependent on receipt of two or more of the plurality of keys.

In some embodiments, the method may comprise generating first, second and third keys, the third key being related to a combination of at least the first and second keys; associating the third key with a particular said set; arranging for the first and second keys to be available for distribution; and granting access to the particular said set in dependence on receipt of either a combination of the first and second keys or the third key.

Usefully, two keys may be required to access certain data. This may in turn be used to ensure that only when two requesting parties work together will access be granted.

The method may comprise associating the first and second keys with respective further sets. The method may further comprise storing the keys and information identifying the sets in a lookup table; and may also comprise identifying data in a set associated with the received key in the lookup table.

In embodiments, the method may comprise transmitting the keys using a first protocol whereby to make the keys available for distribution, and wherein at least a part of the data in a set is suitable for communication via a second, different, protocol. As such, the method may further comprise enabling access to the data using a second protocol.

In some systems, established protocols may not be able to handle certain data. However, in embodiments, the established protocol can be used to distribute the keys, and the data in the sets may be subsequently retrieved using an alternative protocol. Thus the system, and in particular entities using the established protocol need not be updated, and yet any updated entity is able to access additional data, i.e. the data in the sets.

According to a second aspect of the invention there is provided a method of accessing and validating data, the method comprising: receiving a key; making a data access request using the received key; receiving data in response to the request; using a one-way function to generate validation data from information associated with the received data; and validating the received data by comparing the validation data to data derived from received key.

According to a third aspect of the invention there is provided apparatus for enabling access to data by a requesting party, the apparatus configured to: generate a plurality of sets of data; use a one-way function to generate a plurality of keys each associated with a respective one of the plurality of sets, wherein information associated with a said set of data is used as an input to the one-way function when generating a key associated with the set; arrange for the keys to be available for distribution to one or more requesting parties; receive a data access request comprising a key from a said requesting party; and enable access, by the requesting party, to data in a said set, based on the received key.

According to a fourth aspect of the invention there is provided apparatus for accessing and validating data, the apparatus configured to: receive a key; make a data access request using the received key; receive data in response to the request; use a one-way function to generate validation data from information associated with the received data; and validate the received data by comparing the validation data to data derived from received key.

According to a fifth aspect of the invention there is provided a computer program arranged to perform a method of enabling access to data by a requesting party, the method comprising: generating a plurality of sets of data; using a one-way function to generate a plurality of keys each associated with a respective one of the plurality of sets, wherein information associated with a said set of data is used as an input to the one-way function when generating a key associated with the set; arranging for the keys to be available for distribution to one or more requesting parties; receiving a data access request comprising a key from a said requesting party; and enabling access, by the requesting party, to data in a said set, based on the received key.

According to a sixth aspect of the invention there is provided a computer program arranged to perform a method of accessing and validating data, the method comprising: receiving a key; making a data access request using the received key; receiving data in response to the request; using a one-way function to generate validation data from information associated with the received data; and validating the received data by comparing the validation data to data derived from received key.

Further features and advantages will become apparent from the following description of preferred embodiments, given by way of example only, which is made with reference to the accompanying drawings.

Some parts, components and/or steps of the embodiments appear in more than one Figure; for the sake of clarity the same reference numeral will be used to refer to the same part, component or step in all of the Figures.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

FIG. 1shows a communications system1in which a number of requesting parties may access data stored in a data store, such as a database. Within the communications system, the data is stored within, and access to the data is controlled by, an access system10.

The access system10comprises a number of nodes or elements12,14,16,18and20. These include a data source12, which receives or generates data to be stored and subsequently accessed. The data source12is connected to a first database14. A key generator16is connected to the first database14, and is additionally connected to a second database18. An access controller20is connected to the first and second databases14and18.

The key generator16is connected to a number of requesting parties24A,24B and24C via a first network22. The access controller20is also connected to the requesting parties24A,24B and24C, for example via a second network26.

The access system10may be a single device. Accordingly the nodes12,14,16,18and20within the access system may be combined, at least in part—for example a single database device may be used to provide the storage of both databases14and18described above. However this is not a requirement, and the access system10may be distributed, for example by being in the cloud—as such some or all of the nodes12,14,16,18and20may be interconnected network nodes.

The requesting parties24A,24B and24C may be remote from the access system10; accordingly the networks22and26may be local networks, the internet, or proprietary communications networks. While the networks22and26have been described separately—the reason for this will be expanded on below—this is not a requirement and the networks22and26may form a single network.

The operation of the communications system1described above inFIG. 1will now be described with reference toFIGS. 2 to 5. In these Figures, steps which are the same, or at least analogous, will be provided with the same reference numerals. It is assumed that, preceding the steps shown inFIGS. 2 to 5, appropriate data has been generated at, or received by, the data source12. This data may take any number of forms, for example being documents, transaction data, media such as audio or video and/or metadata. The data may be received in data portions, for example individual files, media sections or fields and records in a structured or tabulated form of the data. Alternatively or additionally, the data may be separated into suitable data portions by the data source12. The data portions will be provided with references P1to P9in the examples described below.

FIG. 2shows the operation of the communications system1according to an embodiment. In step102, the data source stores the data, in the portions P1to P9, in the first database14. Following that, in step104, the key generator16communicates with the first database14and generates keys which are associated with the data. To do so, the key generator16generates a plurality of sets of the data portions. Each set identifies one or more of the data portions. The sets may be overlapping, at least in part, such that at least one data portion is identified in two or more sets. A table showing an exemplary distribution of the data into sets S1and S2is shown below.

Here, the data portions P2and P3are identified in both sets S1and S2. Data portions P8and P9are not identified in either of sets S1and S2—a method of accessing these portions will be described below and with reference toFIG. 3.

To generate the sets, the key generator16may retrieve and process all or part of the portions P1to P9within the first database14. A number of different methods by which this may be done will be described in detail below, but for conciseness will not be described here.

Having generated the plurality of sets, the key generator16then uses a one-way function to generate a plurality of keys. Each key is associated with a respective set, as is shown in the following table.

Subsequently, in step106, the key generator16stores the keys and information associating the keys with the sets in the second database18. This data may be stored in, for example, a lookup table.

The key generator16also arranges for the keys to be made available for distribution to one or more requesting parties, such as parties24A and24B. This is shown by step108, where key K1is made available to party24A and key K2to party24B. In this example, party24C does not receive a key, for reasons which will be described in more detail below. With reference back toFIG. 1, this distribution of keys may be performed via the first network22.

The above describes the creation and distribution of keys. The following will describe how these keys may be used to enable access to data for the requesting parties.

In step110, requesting party24A transmits a data access request to the access controller20. The data access request comprises the key K1, which had been received by the requesting party24A in step108. Having received a data access request the access controller20enables access, by the requesting party24A, to the one or more data portions identified in the set associated with the received key, as will be described in detail with reference to steps112to120.

In step112, the access controller20uses the received key K1to identify the set—in this case set S1—associated with the received key. This may be done by performing a lookup in the second database18. Data identifying the set and/or the portions is received by the access controller20in step114. The access controller20then, in step116, retrieves the relevant portions—in this case portions P2, P3and P6—from the first database14. The portions are received by the access controller20in step118and sent to the requesting party24A in step120. Accordingly, access to the portions P2, P3and P6is enabled for the requesting party24A. The requesting party24A is only able to access the portions P2, P3and P6; it is unable to access portions other than those associated with the key K1, i.e. portions P1, P4-P5and P7-P9.

Similar access requests may be made by requesting party24B as shown inFIG. 2by steps122to132. The difference in these steps is that the key received by the access controller20is key K2(instead of key K1) and accordingly the portions returned to the requesting party24B are the portions P1-P5and P7, which are those identified within the set S2associated with the key K2.

As noted above, requesting party24C has not received a valid key; that is, no key was distributed to requesting party24C in step108. Requesting party24C may therefore be assumed to be an attacking party, looking to gain access to the data portions, which is unauthorized. In this example, the requesting party24C uses an invalid key K#. This invalid key K# may be, for example, a guessed or randomly generated key. The request comprising the invalid key is received by the access controller20in step134and used to perform a lookup in the second database18in step136. However this lookup is unsuccessful as there are no sets or portions associated with the invalid key K#. The access controller20receives notification from the second database18that there are no associated portions in step138, and consequently the access controller20denies requesting party24C access to any of the data portions. This may include, in step140, the access controller transmitting a rejection message to the requesting party24C; however this is not required, and the access controller20may simply ignore the request made in step134without making a response.

The above describes a first method of enabling access to data according to embodiments. By generating the sets, and associating the set with the keys, embodiments are able to efficiently control access to overlapping sets of data portions—i.e. where two sets identify the same data portion. Moreover, should a key be compromised—that is the key is known to a party which is not authorized to access the data—the only changes which need to be made are to the association between the keys and the sets. For example, a new key may be generated and associated with the set which was previously associated with the compromised key. The compromised key may then be revoked, deleted or suppressed. This is more efficient than the encryption system described in the background section as no re-encryption is required.

One-way functions, used to generate the keys, are functions designed such that it is easy to compute the output using the input, but difficult to compute the input using the output. They are known in the art, and therefore will not be described in detail.

A one-way function (use to generate the keys) is a mathematical function that is significantly easier to compute in one direction (the forward direction) than in the opposite direction (the inverse direction). It might be possible, for example, to compute the function in the forward direction in seconds but to compute its inverse could take months or years, if at all possible. A one-way function will give an output that is un-predictable and equally distributed throughout the key space (the key space being the range of possible values which the key may take).

As a consequence of using a one-way function, a third party will be unable to create valid keys to use to access the data, and thus the only source of a valid key is via distribution from the key generator16. This provides improved security to the system as the distribution of the keys can be controlled and used to restrict access to the data and as the key itself provides a means to authenticate the requesting parties and thus control access to the data. Moreover, should a key become compromised, only the set of data portions associated with that key are vulnerable to attack, rather than the data as a whole. This can also be contrasted to a system where a key merely represents requested data in the clear. Such a system can enable the distribution of data, but cannot prevent an attacking party from changing the form of the request and thereby accessing different data portions.

Examples of appropriate one-way functions include random or pseudorandom number generators, hash functions (the application of which will be described in more detail below), and so-called “trapdoor” one-way functions. A trapdoor one-way function is a one-way function for which the inverse direction is easy given a certain piece of information (the trapdoor), but difficult otherwise. For example, public-key cryptosystems may be based on trapdoor one-way functions. The public key gives information about the particular instance of the function; the private key gives information about the trapdoor. Whoever knows the trapdoor can compute the function easily in both directions, but anyone lacking the trapdoor can only perform the function easily in the forward direction. The forward direction is used for encryption and signature verification; the inverse direction is used for decryption and signature generation.

The use of keys provides a number of advantages over a system which uses, for example, a username/password based authentication system. Firstly, they keys enable a much greater granularity to access control—that is, a given requesting party may be provided with a plurality of keys, each enabling access to different portions of data. This can be illustrated by the following table. Here the data portions represent fields in a database structure. The database structure further separates the data into records, each comprising the portions (i.e. fields) P1to P9. Sets of portions may be created for each record, as shown in the table below.

Therefore to continue the example above, a key K1R1may be associated with a set S1R1, which is in turn associated with the portions P2R1, P3R1and P6R1in the first record R1. Similar keys K1R2, K1R3, K2R1etc. may be created and distributed for other sets of portions in the various records. A requesting party may be provided with one, or a combination of, the keys, and thus be provided with a highly controllable access to the data.

A further advantage is that requesting parties may share keys with other parties, and thereby enable those other parties to access the data portions associated with the shared key. This can be done without having to provide credentials, for example, a full username and password to that other party, which can severely compromise the security of the system, as well as providing the other party with access to everything accessible via that username and password, rather than specific data.

The keys may have high entropy. That is the one-way function used to generate the key is designed to have a high entropy output. Entropy, in this context, is a measure of unpredictability or randomness in the generated keys and here relates to the number of equally possible keys which may exist. High entropy in turn means that the number of equally possible keys is sufficiently large to make a brute force attack to find a much smaller number of valid keys impractical.

For example, in a relatively low security system, the key may be a 16 bit word equating to approximately 65,000 possible keys, and approximately 50 (˜26) keys may be distributed. This gives a ratio of possible to valid keys of approximately one thousand (103 or 210) to 1. In a higher security system, the ratio may be one billion (109 or 230) to 1 or higher. For example the key may be a 64-bit, 128-bit, 256-bit (or higher) number or word, equating to approximately 1019 (264), 1038 (2128), or 1077 (2256) possible keys. In such a system, even if approximately one billion (109 or 230) keys are distributed, the ratio of possible to valid keys will be in excess of 1010 (˜234) to 1, 1029 (˜298) to 1 and 1068 (˜2226) to 1 respectively. It will be appreciated that factors, such as the algorithm used to generate the keys, the number of requests which can be processed, the number of keys which are to be distributed and the capabilities of the devices requesting the data for handling large keys will determine whether a given key length has high enough entropy for the design purposes of the system.

A further factor, which may be taken into account when determining whether a key length has high enough entropy, relates to the probability of there being a collision between two equal valid keys. This may happen if there are a large number of valid keys, even if the number of possible keys is large. The number of valid keys to be used may be estimated, and the key length selected to give an entropy which provides a risk of collision below an acceptable level.

Sufficient key entropy is one way of mitigating a known attack, referred to as the birthday problem. For example, in a system using 64-bit keys, if approximately 100 million (108 or 227) keys are valid then the probability of two valid keys being equal is less than 1%. However, if 100 times that number of keys, i.e. 10 billion keys (1010 or 233), are valid, the probability of a collision (i.e. there being two equal valid keys) is greater than 99%. Depending on the nature of the system, how the keys are generated and the relationship between the keys and the data, this may or may not be a problem. Nevertheless, the probability of finding (e.g. guessing) any valid key, will be a factor in determining whether a given key length has sufficiently high entropy for the desired security of the system.

In some embodiments, for example, the nature of the data accessible using the keys may be arranged such that a high probability of finding a valid key is not a problem. For example, where the keys are used to control access to multimedia such as video, a collision may provide a party with access to data portions representing a small section of a single video. This may not be seen as a problem, as that party will not have access to the remainder of the video, and thus is provided with little value (i.e. the whole video). Therefore, in such systems, the probability of collisions may be high and yet the key may still have high enough entropy. By contrast, if the data portions represent commercially sensitive data, such as financial data, then a party gaining access to even a small quantity of the data may represent a security problem, and thus the probability of collisions must be made significantly smaller for the key to have high enough entropy.

The one-way function used by the key generator16may be a pseudo-random number generator, as are known in the art. Alternatively the key generator16may be arranged to generate a random number using an unpredictable input, for example temperature or the movement of the head of a disk drive. This generates a random number—sometimes called a true random number—which is less deterministic than a pseudo-random number. Such systems are again known in the art, and use a one-way function to create values which are evenly distributed over a desired range of values. In this context, the one-way function is sometimes called a randomness extractor. In either case, while the keys will enable access to given data portions, the values taken by the keys will have no direct relationship with the data portions themselves.

In the alternative, therefore, to generate the keys, the key generator16may use information associated with the data portions as an input to the one-way function. This information may be associated with the data portions within the set of data portions to be associated with the key. The information may comprise at least a part of the content of the data portions, alternatively of additionally, the information may identify the data portions, for example being metadata, portion identifiers, filenames, or the like.

Where the keys are generated using information associated with the data portions, the one-way function may comprise a hash function. The hash function reduces the length of the input information to a desired length, i.e. the length of the keys. Typically the hash function will also produce an output with high uniformity meaning that the expected inputs are mapped evenly over the output range. This has the additional effect that a small change in the input will typically result in a large and unpredictable change in the output.

In embodiments, the one way function may comprise a cryptographic signing function, which may be combined with the hash function mentioned above. Where the two are combined, the hash function may be used on the information, and the hashed result signed.

The advantage of generating the keys using information associated with the data portions (for example identifying information such as metadata, or the actual content of the data portions themselves) is that the key can serve a dual purpose. That is, the key not only enables a requesting party to access the data portions, but also enables the requesting party to verify that data portions to which access is enabled are genuine. As a consequence, security is enhanced, since any changes to the data portions, between the keys being distributed and the data portions being retrieved, will be detectable.

In embodiments, all of the data may be used to generate the key, this in turn enables the validity of all of the data to be verified. However in alternative embodiments, only a part of the data may be used to generate a key—this part may be, for example, more sensitive than other parts of the data.

Where only a hash is used, the requesting party will be able to verify the integrity of the received data portions by comparing the hash of the information associated with the received data (which was used to generate the key) with the key itself. If the two match, then the received data portions may be taken as genuine, and/or the requestor has assurance that the data has not been accidentally or maliciously modified since the key was generated. To enhance security, the key may be signed. In which case the receiving party may not only determine that the data is genuine, but may confirm that the correct entity generated the key, i.e. the system offers the requester assurance of non-repudiation. The use of e.g. public/private keys to sign data and to verify data is known and will not be described in detail.

Further embodiments may use information associated with the portions, without providing any ability for verifying the integrity of the data. For example, the data itself may be used as the input to a one-way function merely to increase the unpredictability of the keys generated. In effect the information associated with the data forms the unpredictable (or at least less predictable) input in the true random number generator described above. In such cases, any number of one-way functions may be used, so that an evenly distributed output is produced.

In some embodiments, it may be desirable to have each given set of data portions associated with only a single key. Thus, if two requesting parties are to be allowed access to that set of data portions, they will receive the same key. This may be desirable in a system where keys are intended to be shared between requesting parties, and enables the number of keys to be kept low.

However, in the alternative, it may be desirable to provide each requesting party with different keys, irrespective of what data portions are to be accessed using those keys. In such embodiments an additional value, sometimes called a salt value, may be included as an input into the one-way function. This enables two different keys to be created for the same set of data portions. Since the keys are different, the requesting party making the request can be identified, meaning that if an unauthorized request is made using a valid key, the authorized requesting party from which the key was obtained can be identified.

If the keys are to be used to validate the data portions (see above) and are generated using salt values, the requesting parties may need to know the relevant salt values (e.g. if integrity checks on the data are required)—otherwise the requesting party will be unable to generate a valid hash. In this case the salt values may be made available with the keys, for example, the salt values and the keys may be distributed together. In other embodiments, the salt values may be made publically available in a lookup table.

Alternatively, a pre-shared secret value or values may be specific to a given requesting party—in other words, a prior arrangement ensures that the requesting party knows what pre-shared secret value or values are to be used (may be in a similar manner as a salt value).

In yet further embodiments, the salt values may be stored with the data portions, for example by creating additional data portions representing the salt values. In the following example, two different keys (here K1aand K1b), access the same set portions of the original data, portions P2, P3and P6. However in each case, the portions of data are augmented with salt value portions, Pa and Pb. As a consequence, the keys generated using the data portions are different. This is summarized in the table below. It will be understood that the validation of the received data is possible without modification as the received portions will include a salt values Pa or Pb.

As mentioned above, the keys may be distributed via first network22, while the access requests, and the portions of data sent in response, may be transmitted through a second network26. This provides the advantage that the first network22, used to distribute the keys, may be provided with a higher level of security in comparison to the second network26. In some embodiments, the first network22may be replaced by an alternative method of providing the keys—for example physical transportation of the keys on a physical media. Either way, the keys may be kept relatively secure, while the access to the data portions is enabled using a relatively less secure network. In embodiments either or both of the first and second networks22and26may be cryptographically protected using e.g. SSL or TLS.

A further advantage is that embodiments facilitate access to data using an existing, or legacy, protocol, when that existing protocol is constrained in terms of the amount of data that can be transmitted, and it is inconvenient or expensive to modify the protocol. For example, the first network described above may support such a first protocol. The keys, which are relatively small in terms of number of bytes, may be distributed using this first protocol, while the data portions may be transmitted via a second protocol, which is unconstrained in terms of type and amount of data that can be transmitted. This ensures backward compatibility, as devices can still access the data portions—via the keys that are transmitted over the first protocol.

It will be appreciated that the keys and associated sets of portions may be stored in a number of formats within the first database14and second database18. For example, in one embodiment, the keys may be directly associated with portions as follows. Thus information explicitly identifying the sets does not need to be stored.

In other embodiments, a relational database structure may be used, for example a first table may associate keys with sets:

and a second table may associate sets with portions:

This latter structure provides the advantage that only a single field in a single table needs to be modified if a key is compromised or needs to be revoked. Equally when a new key is issued, only a single record needs to be updated. In some embodiments, the second table, associating the sets with data portions may be stored with the data portions themselves, i.e. in the first database14. In such cases, the responses from the second database in steps114and126above may contain an identification of a set, if a key is valid, and the requests in steps116and128may be for a given set of data.

While in the above method, a given request resulted in the provision of all data portions associated with the key provided in the request, some embodiments may allow the requesting parties to identify portions when making a request. Therefore, for example, in step110, the requesting party24A may provide key K1, and request only portion P2. As a result, in step120, the access controller20may provide only data portion P2to the requesting party24A.

WhileFIG. 2shows a first method of enabling access to data using keys,FIGS. 3 to 5will be used to illustrate variations which may be incorporated into, or substituted for, the method described above.

FIG. 3illustrates a method which utilizing combined keys. This method will be described in detail below, but in overview the method enables certain portions to be access only by two or more parties acting together. This increases security for more sensitive data as both parties are required to provide their keys to enable access.

Steps102to108, the generation of sets of data portions and association with keys progresses in a similar manner to that described above. However in this case three keys may be created as follows:

The third key, K3is based on a combination of the first and second keys. The third key may be generated, for example, as a function of the first and second keys such as a concatenation or a bitwise exclusive-or (XOR) of the first and second keys. It will be appreciated that other functions, including one-way functions, may be used. Alternatively, the third key may be generated, and then itself used to generate the first and second keys—for example by splitting the third key into parts, or by calculating the first and second keys using the third. Whichever method is used, the third key can be derived from knowledge of the first and second keys.

As shown above, the third key is associated with a third set S3which identifies portions P8and P9. In this example the first and second keys K1and K2are associated with sets S1and S2respectively; however this is not a requirement, and one or both of the first and second keys K1and K2may not be associated with any set of data portions. In effect, while the third key provides access to a particular set of data portions, it does not have to be distributed to recipients. Instead it represents a particular combination of other keys; these other keys are distributed to recipients and these keys are required by the access controller20for the access controller20to return data portions relating to this third key. In this regard the first and second keys can be considered to function as surrogates for access to a particular data set associated with the third key.

Accordingly, the first and second keys are made available for distribution in step108. Specifically, in this example, key K1is made available to requesting party24A, and key K2is made available to requesting party24B. The third key is not distributed, which is to say that no requesting party will receive the third key.

Following the distribution of the first and second keys in step108, the requesting parties24A and24B cooperate to combine the keys and to request access using the combined keys. One method of doing this is shown inFIG. 3. In this example, it will be assumed that the access controller20has identified that access will be requested using multiple keys. This may be in response to one of the parties indicating that a multi-key request is being made in a given request, or by the request identifying data portions which can only be accessed using multiple keys.

Accordingly, in step146the requesting party24A sends a request comprising the key K1to the access controller20. In addition, in step148the requesting party24B also sends a request, this one comprising the key K2, to the access controller20. Having received both keys, the access controller may, in step150, generate the third key K3using the first and second keys K1and K2. This third key K3is then sent to the second database18in an analogous step to steps112and124above. As there is a set of data (set S3) associated with the key K3, the access controller in step154receives data identifying the set S3or the portions thereof (portions P8and P9) from the second database18. The access controller in step156then retrieves the portions P8and P9from the first database14, and provides the portions to one or both of the requesting parties24A and24B. Therefore, only by combining the keys can the two requesting parties gain access to the portions P8and P9.

In addition to combining the keys, the requesting parties may act independently and retrieve any portions which are associated with the individual keys distributed to the parties. This is shown inFIG. 3in steps110to120which are the same as steps110to120above, and show the first requesting party24A accessing portions P2, P3and P6using the key K1. As mentioned above, the keys K1and K2do not have to be associated with any sets of data portions. Accordingly, in an alternative embodiment, a request using key K1may result in a rejection as for an invalid key, described in steps134to140above.

Thus embodiments provide an efficient system for enabling selective access to portions of data not only to individual parties, but to parties acting together. To coordinate the actions of the two parties, a key may be requested from one or other of the requesting parties by the access controller20. For example, a first requesting party, e.g. requesting party24A, may request access to data and identify that the requesting party24B is also required to provide a key. As a consequence, the access controller20may communicate with requesting party24B to request the key K2. Alternatively, the requesting party24A may request access to e.g. portions P8and/or P9, and the access controller may store data enabling it to contact the second requesting party24B to request the appropriate key. Other methods of communicating between the parties so that both provide keys will be evident to the skilled person.

Therefore, a second requesting party (e.g. party24B) may be provided with the ability to allow or refuse access for a first party (or vice versa). Thus embodiments may be used in a scenario where one user controls access to data for at least one other user. In practice, the second requesting party may be an administrator who has the ability to grant or refuse access for any one of a number of member parties. In such embodiments, a single administrative key may grant access to different sets of data portions when combined with different member keys. Thus a member key may be considered as an identifier of a given set of data portions, and the administrator key an access control key for those data portions.

In some embodiments, the function used to combine the keys may be arranged such that, even though the requesting parties24A and24B have knowledge of the individual keys K1and K2, these parties will be unable to generate the key K3if they are only in receipt of one key. This level of control may be enforced by using a function such as a one-way function within the access controller20to generate the key K3. This has the advantage that two parties need to provide the keys K1and K2individually to the access controller20to gain access to the data portions P8and P9.

In the alternative, the key K3may be a calculated combination of keys K1and K2. In such embodiments, one or both of the requesting parties24A and24B may receive a key from the other. The requesting party that receives a key from another party may then combine the keys to produce the key K3, which is used in a request for access to data. That party will then be able to access the data portions P8and P9as if that party had been originally provided with the key K3in the distribution. Such embodiments provide the advantage that only a single access request, using what amounts to key K3, is required to access data, and avoids the access controller20making a request to another party for a key. It will be appreciated that the system used may be tailored in dependence on the intended purpose of the system.

While the above embodiments have been described in terms of a key K3being associated with data portions, it will be appreciated that the access controller20and second database18may be arranged such that an access request or requests comprising multiple keys may lead to access being granted without actually requiring determination of an intermediary key, i.e. key K3. This has the advantage that the number of keys is reduced; however, the use of a determined key, such as key K3, provides the advantage that the arrangement of the database18is simplified, since the database18will not have to store any additional information indicating that multiple keys are required.

In some embodiments, the keys to be combined may be sent to different requesting parties. However this is not a requirement, and the keys may be sent to a single requesting party. The keys may be sent using different communications systems—e.g. one key is sent via a SMS, the other via email—or at different points in time. Thus embodiments can be used to enable access to a party in more complex scenarios.

In some embodiments, keys may only be used a limited number of times. Two examples of such embodiments are described inFIGS. 4 and 5. In both examples, a given key may be used only once; however this is not a requirement, and a given key may be used multiple times, albeit still a limited number of times.

A first example is shown inFIG. 4. As before in steps102to108, the portions are stored in the first database14and the keys are distributed. As with the method described above, the requesting party24C does not receive a key. However, in the scenario of this embodiment, the requesting party24C has compromised the system of requesting party24A. As such, the requesting party24C is able to acquire a copy of the key K1when it is used by the requesting party24A. This is shown in steps110and110′. In step110, as with step110above, the requesting party24A sends a request, comprising the key K1, to the access controller20. However, in addition, the key K1is received, in step110′ by the requesting party24C.

Steps112to120follow the steps of the same number described above, and result in the requesting party24A being able to access the portions P2, P3and P6. However, following the granting of access to these portions, the access controller sends a message to the key generator16informing the key generator16that the key K1has been used. This is shown as step162. In response to the message in steps162, the key generator generates a new key to be associated with the set S1. In step164the second database18is updated to reflect that the key K4now associated with the set S1, and thus with portions P2, P3and P6. The key K1is revoked and may be removed from, or suppressed within, the second database18. In addition, the key generator16makes the new key K4available for distribution to the requesting party24A, as shown by step166. In effect, key K1is replaced by key K4. The key K4may be generated using e.g. a different salt value to key K1, as was described above. If the salt value is to be stored with the data, i.e. as a portion (e.g. Pa and Pb) then the data may be modified to contain the new salt value.

In some embodiments, the new key K4may be generated prior to the accessing of the data portions by the requesting party24A. The new key may consequently be made available to the requesting party along with the data portions. In other words, steps120and166may be combined.

As described above, in the meantime (step110′), the requesting party24C has gained access to the key K1. The requesting party24C therefore attempts to use this key to access the data by sending a request, comprising the key K1, to the access controller in step168. As with steps136to140above for key K#, the key K1is not valid, and consequently the request is rejected.

Thus, the method above may be used to improve the security of the system, and reduce the opportunity for attacking parties to gain access to the stored data using intercepted or stolen keys.

The replacement of keys may be used in combination with the system described above where multiple keys are required for access to certain sets of data portions to replace a used key. In embodiments, only a subset of the keys used for a multi-key request may be replaced. For example, in the embodiment above, each request may result in the administrator key being replaced, but not in the user key being replaced.

A further method, in which keys are only used once, is shown inFIG. 5. This method differs from that shown inFIG. 4in that a plurality of keys, each associated with a single set, are generated initially and distributed together. This is represented by steps106′ and108′, where keys K1.1, K1.2, . . . K1.N are all associated with set S1and are distributed to the requesting parties24A and24B. Each of the keys K1.1to K1.N may be generated using a different salt value.

In steps110to120, as with the same numbered steps above, the key K1.1is used by the requesting party24A to request access to the data portions associated with that key, i.e. the data portions in set S1. As before, access to these data portions is granted in step120. However, following step120, the access controller20, in step176, sends a message to the second database18to revoke, delete or suppress the key K1.1as it has now been used.

Subsequently, in step178, a further attempt is made to request the data portions in set S1corresponding to the keys K1.1, K1.2etc. In this example, both requesting parties24A and24B have been provided with the same set of keys. Moreover, requesting party24B is unaware that the key K1.1has been used. Therefore in step178the requesting party24B requests access to the data using the key1.1. However, since the key K1.1is no longer valid, this request is handled in a similar manner to the request described in steps134to140above, and is rejected. It will be appreciated that this would be how any further request using the key K1.1would be handled—i.e. if the request had come from requesting party24C who had gained the key K1.1by intercepting it from requesting party24A as described in step110′ above.

However, since the requesting party24B has knowledge of a plurality of suitable keys, i.e. keys K1.2etc., the requesting party24B may make a further request using a further suitable key. This is shown in step122, where the key K1.2is used in a request. This request is effectively handled as per original request122above; steps122to132follow, with access being enabled for the portions of data associated with the key K1.2. As per step176above, step132may be followed by the key K1.2being deleted or suppressed in the second database18, as shown by step186.

While the above only describes two keys being used, any number of keys may be issued, and any party may have to make request using a much larger number of keys before one is accepted. It will be understood that any given requesting party may keep a record of keys which have been used. Therefore, for example, should the requesting party24A make a further request for the data, it would make a first attempt with key K1.2, as it will know that key K1.1has been used already. It will be appreciated that this request would be rejected, as the key K1.2has been used by requesting party24B, and therefore the requesting party would have to use a key K1.3etc. until a request is granted.

While the above embodiment is described in terms of two parties being provided with the same keys, in other embodiments the parties may be provided with different keys, yet still be allowed access to the same set of data using those keys. This avoids one party being denied access based on the other party using a given key.

Alternative Details and Modifications

While the embodiments above have been described separately, it will be appreciated that features from one may be combined with features from another. For instance the combined key embodiment, shown inFIG. 3may be combined with a mechanism for using keys only once, as described in e.g.FIG. 4.

Embodiments described above may be combined with other forms of access control, for example authentication using a username and password, to increase the security of the system as a whole. In such cases, a key may be associated with a username, and thus access will only be granted to an authorized user who is in possession of a key associated with that user.

In the embodiments described above inFIGS. 2 to 4, a single key is provided at a time to a given requesting party. However in other embodiments, a single key may be provided to multiple parties. Alternatively or additionally, multiple keys may be associated with a single set, the key being provided to multiple requesting parties. This enables the parties to access the same data, but for a log to be maintained over which party has made a given access request.

In the multi-key embodiment described with reference toFIG. 3, a given portion of data may be accessible using different combinations of keys. As a consequence, a first requesting party may request access to data using a first key. In response the access controller may request a second key from one of a plurality of second requesting parties. A response (containing a key) from any one of the second requesting parties will grant the first party access to the data. Thus the keys may be used as a method to confirm an access request.

InFIGS. 4 and 5the keys are described as being usable a limited number of times. However this may not be the only reason that a key is revoked, deleted or suppressed. For instance, a key may have a validity for only a certain period of time, after which it is revoked, and a replacement distributed. In embodiments, time based revocation may be combined with limited use revocation, meaning that once a key is used once, it is valid for a given period of time, during which it may be used any number of times, and after which it is revoked.

While the above has generally been described with a limited number of keys, typically two, embodiments are applicable to a system utilizing a larger number of keys. This may enable access to be controlled for a large number of sets, or for a large number of parties. Furthermore, more than two keys may need to be combined for the combined access described in relation toFIG. 3.

The access system10, or the nodes or elements12to20, may comprise computerized hardware as is known in the art. For completeness, an exemplary computerized system50, capable of performing the method steps described above, will now be described with reference toFIG. 6. This computerized system may be used to perform the function of the access system10as a whole, or a number of the computerized systems50may be used, each performing the function of one or more of the nodes12to20described above.

The computerized system50comprises a processing system51, such as a CPU, or an array of CPUs. The processing system51is connected to a memory52, such as volatile memory (e.g. RAM) or non-volatile memory, for example a solid state (SSD) memory or hard disk drive memory. The memory52stores computer readable instructions53. The system50may also comprise an interface54, capable of transmitting and/or receiving data from other network nodes.

In use the processing system51may retrieve the computer instructions53from memory52and execute these instructions whereby to perform the steps described above. In so doing, the processing system51may cause the interface to transmit or receive data as required. This data may itself be stored in memory52, and retrieved as required—for example to be transmitted via the interface.

It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims. The features of the claims may be combined in combinations other than those specified in the claims.