Patent Application
20110145585
The following relates to systems and methods for providing credentials.
Data communication networks are often used to transfer data between computing devices, for particular users or the devices themselves, either of which may be commonly referred to as correspondents or entities or both, and have become ubiquitous with modern commercial activities. Cryptographic systems may be deployed to achieve security goals such as confidentiality, data integrity, data origin authentication, entity authentication, and non repudiation.
Symmetric key cryptographic systems achieve these goals by sharing a common secret key between two correspondents.
Public key cryptography utilises a public/private key pair for each correspondent. The public key and private key are mathematically related such that computing the public key from the private key is relatively simple but recovery of the private key from the public key is considered computationally infeasible. The private key is maintained secret at all times but the public key is distributed or made available to other correspondents.
Public key cryptography enables a message from a sender to be encrypted using the public key of the intended recipient and further enables the message to be recovered by the recipient using the corresponding private key, which is known only to the recipient.
Messages may also be signed by the sender using the sender's private key and the signature may then be verified by a recipient using the sender's public key.
Many protocols have been developed to perform encryption, signing and key agreement using public key cryptography. It is however inherent in these protocols that the public key being used is in fact associated with the appropriate correspondent or entity and is not that of an interloper purporting to be that correspondent, referred to as entity authentication. In order to provide entity authentication, a hierarchy of trust may be established.
For example, a pair of correspondents who wish to correspond can rely upon a third party that they both trust. The third party, referred to as a certificate authority (CA) may be, for example, a bank, a service provider, or a manufacturer to name a few. The CA has a public/private key pair and the CA's public key is available to and trusted by each of the entities. The CA public key may be, for example, embedded in the correspondent's computing device at manufacture or sale and is used to verify the signatures on messages sent from the CA to one or both of the correspondents.
When one correspondent wishes to distribute her public key to other entities, she may ask the CA to sign a message containing her public key, which confirms that the public key belongs to her. The message and the signature may then be sent to the other entity who uses the CA's public key to verify the signature and thereafter use the sender's public key with confidence.
The formatting of the message and signature is referred to collectively as a certificate that is issued by the CA. It will be appreciated that the hierarchy may extend through multiple tiers so that the CAs may themselves have a common trusted third party, and so on, back to a root. In this way, the trust may propagate through different layers of the PKI and facilitate the transfer of information throughout the network.
To provide interoperability over a wide network, it is desirable for the certificates to share a common format. The certificates typically comprise data strings and in order to be able to extract information from the string, the correspondent needs to know the format of the string. The format of the certificates may therefore be standardized or otherwise define a specific format, to allow each correspondent to utilize the certificates issued by the CA.
One standard for certificate formatting is ITU-T X.509 (hereinafter ‘X.509 ’ for brevity). These certificates are issued from a CA after processing a certificate request, such as a PKCS#10 certificate request file.
Alternative certificate formats may have particular characteristics, such as an ability to be used at a reduced bandwidth, making them particularly suitable for constrained environments such as wireless communications. For example, the Elliptic Curve Qu-Vanstone (ECQV) protocol offers a method for creating implicit certificates and therefore can offer significant bandwidth savings.
Embodiments will now be described by way of example only with reference made to the accompanying drawings in which:
The use of a particular cryptographic protocol typically requires a certificate request and the generation and provision of the certificate that conforms to a specified format for that protocol, or that conforms to a specification or standard related thereto, to be provided throughout the system incorporating the protocol, for example a PKI. Whilst this is technically feasible, it does require all levels of the trusted hierarchy to be able to process such requests and generate or otherwise provision such certificates. It has been recognized that this may be considered an unnecessary burden by some participants in the system, particularly where an alternative standard or specification is only considered for use in a specialized area or application and therefore implementation of the alternative standard or specification is hindered.
In general terms, the following provides a method of providing credentials by, for example, providing a certificate from a CA in response to a request according to a first specified format. In such examples, the certificate incorporates in the certificate structure or format, supplementary information to permit the requestor to create and use a certificate of a second, different specified format.
The certificate issued by the CA complies with the first specified format e.g. according to or derived from a particular standard, and therefore may be distributed through the system (e.g. PKI) in the normal manner.
The requestor who wishes to conduct an exchange of information using the second specified format, e.g. according to or derived from another standard, may extract the supplementary information from the certificate and utilize it to enable communication according to the second specified format.
The supplementary information in the embodiments described below includes the necessary information to transform the certificate from the first specified format to the second specified format. For example, this may include an implicit certificate and private key contribution data used by the requestor to construct a private key corresponding to a public key bound in the implicit certificate.
Referring therefore to
The correspondents 12 communicate through communication links 16 that may include the internet 16a, wireless network 16b, or a private network 16c; and employ addressing and routing protocols commonly used to control and direct the flow of information through the network.
As can best be seen in
It will be appreciated that the cryptographic module 24 may be incorporated within the processor 20 so as to be physically coextensive but functionally it provides a distinct secure environment to perform cryptographic operations. In embodiments, the processor 20 may itself perform the operations of the cryptographic module 24.
It will be appreciated that the cryptographic modules 24 and processors 20 exemplified herein may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by cryptographic module 24 or processor 20 or both. Any such computer storage media may be part of the respective correspondent 12 or accessible or connectable thereto.
The correspondents 12 may be arranged in a hierarchy of trust and in the embodiment shown, the server 12c includes a cryptographic module 24 that functions as a certificate authority, CA. The correspondents 12 that trust the CA may have the public key of the CA embedded in the registers 26 to establish the trusted relationship. The correspondents 12 can communicate through the data links 16 and the processor 20 may call upon the cryptographic module 24 to perform cryptographic functions such as signing messages, verifying signatures and encrypting messages in accordance with the protocols selected by the processor.
Each of the cryptographic modules 24 stores the parameters for the cryptographic system to be implemented. In embodiments, the correspondents utilize an elliptic curve cryptosystem (ECC) that utilizes the intractability of the discrete log problem in an elliptic curve group defined over a finite field. The elliptic curve group comprises the points that have elements of the underlying field as coordinates and that satisfy the equation of the elliptic curve. In a typical application, the field Fp is the field of integers modulo p and the elliptic curve E is defined by an equation of the form y2=x3+ax+b, where a, b, εFp. A pair (x,y), where x, yεFp, is a point on the curve if values (x,y) satisfy the equation of the curve.
The parameters of the cryptosystem stored in the registers 26 include the values of a, b to define the curve being utilized; a base point P, that is a generator of the points forming the elliptic curve group; and the order, n, of the point P.
A private key, k, is an integer generated at random and lying in the interval [1, n−1], and the corresponding public key Q is obtained by a k-fold group operation on P. As the elliptic curve group uses additive notation, the corresponding public key Q=kP. The establishment of an elliptic curve cryptosystem is well known and is more fully described in the Guide to Elliptic Curve Cryptography by Hankerson et al., available from Springer under ISBN 0-387-95273-X, the contents of which are incorporated by reference.
In the example shown, each of the correspondents 12 has a key pair k, Q which may be considered long term or static key pairs. An ephemeral or short term key pair k′, Q′ may also be generated by the cryptographic module 24 using the RNG 30 to obtain the short term private key k′ and the ALU 28 to compute the short term public key Q′.
In order for the correspondent 12a to communicate with correspondent 12b over links 16, the correspondent 12a needs to provide its public key QA. To authenticate the correspondent 12a to correspondent 12b, the public key QA is included in a certificate 40 that is signed by the CA, 12c. The certificate 40 is sent to the correspondent 12b who uses the public key of the CA embedded in the registers 26 to verify the signature on the certificate 40. The public key QA may then be extracted from the certificate 40 and used with confidence.
A format of a certificate 40 (e.g. the structure of a certificate 40) that is compatible with the X.509 certificate formatting standard is shown in
A pair of extension frames 62, 64 are incorporated into the certificate 40 to include supplementary information in the form of a certificate for use with a second standardized/specified protocol. In the example embodiment disclosed in
The certificate information 42 is exemplarily signed using an ECDSA signature protocol (ANSI X9.62 standard) and the signature components, (r,s) appended to the certificate information 42 as the signature 44. An example specification of the certificate 40 is as follows.
The certificate 40 in this example is compatible with the standardized X.509 certificate formatting and therefore widely accepted in the network, and the incorporation of the ECQV implicit certificate and private key contribution data, t, enables selective use of the second format used in a second protocol between correspondents 12.
The provisioning of the credentials, e.g. by way of certificates 40 to the correspondents 12, is shown in
Correspondent 12a is directed to send a communication to correspondent 12b. Correspondent 12a has a static key pair kA, QA. The communication is initiated by requesting a certificate 40 from the CA 12c for the public key QA, of correspondent 12a. The requestor, correspondent 12a, sends a request to the CA, 12c, in accordance with the requestor transformation of the first standardized protocol, in the present example, X.509.
The request includes identification information, indicated in
The request is received by the CA, 12c, which verifies the contents of the request, including verification of any signature on the request. The CA, 12c validates the identification information according to the policies implemented by the CA, 12c, such as by a challenge/response exchange between the CA, 12c and the requestor 12a.
Upon validation of the identity, the CA formats the certificate structure using the information received from the requestor. Prior to signing the certificate 40, the CA also generates a certificate corresponding to the second protocol and inserts that into the extension fields. The CA, 12c has two static key pairs, (kCA, QCA) and (k′CA, Q′CA) and uses one for the certificate of the first standardized protocol and the other for the second standardized protocol.
In embodiments in which the second format and second protocol is associated with ECQV, the CA generates an ephemeral key pair (d,Q) using the RNG 30 and ALU 28 of its cryptographic module 24.
The CA, 12c, computes a public key reconstruction value BA=Q+QA and constructs identity and validity information, denoted by IDA. This information may be obtained from that previously constructed by the CA, 12c for use in the certificate information 42 if convenient.
The CA 12c then formats an ECQV certificate ICA, to contain the values BA and IDA. The format of the certificate ICA is shown in
The certificate ICA is used to generate private key contribution data, t, by initially hashing the certificate ICA to obtain a hash value e, i.e., e=hash (ICA).
The private key contribution data, t, is then generated using the hash value, e, the ephemeral private key d, and the CA's second static private key k′CA so that t=ed+k′CA.
The certificate ICA and the private key contribution data, t, are inserted into the extension fields 62, 64 respectively of certificate 40 which, in this example, is then signed using the ECDSA signature protocol. A worker skilled in the art would appreciate that other signing protocols may be used instead of ECDSA for signing said certificate 40.
The ECDSA signature protocol uses the CA's primary key pair (kCA, QCA) as long term keys and generates an additional ephemeral key pair (g, G) for performing the signature protocol. The CA 12c generates an integer
The certificate 40, which includes signature components r, s, is returned to the requestor, namely correspondent 12a in this example, who can verify the signature by computing a hash value e′ of the certificate 40. Values w=s−1 mod n, u1=e′ w mod and u2=r·w mod n are computed and combined to obtain a value representing a point value X=u1P+u2QCA.
The value X is checked to ensure it is not the point at infinity and the x coordinate x1 of the value X is converted to an integer
The correspondent 12a may use the certificate 40 in communicating with other correspondents, 12b, who may also verify the signature, by using the components r,s and the public key QCA of CA 12c. The public key QA is then extracted from the certificate. The certificate 40 is compatible with the first specified format, e.g. conforming to the X.509 standard, even though it contains the supplementary information in the extension fields 62, 64.
If, however, the correspondents 12 prefer to use the second protocol, the certificate ICA and the information necessary for the correspondent 12a to generate the private key and corresponding to the public key are available in the extension fields on the certificate 40.
As shown in
The private key k′A may then be used in conjunction with the ECQV certificate ICA. Correspondent 12a can forward the implicit certificate ICA to a recipient, for example correspondent 12b. To obtain the public key Q′A corresponding to k′A, and bound to the implicit certificate ICA the recipient 12b extracts BA from the certificate ICA and computes e″=hash(ICA) The public key Q′A is then computed as e″BA+Q′CA.
The use of the second protocol is therefore available to the requestor 12a if needed but the initial distribution of the certificate ICA to the requestor can be achieved using the certificate 40 and infrastructure associated with the first protocol.
In the event that the recipient of the certificate 40 does not need or wish to use the second protocol, the inclusion of the supplementary information will not affect the use of the certificate 40.
After recovery of the private key k′A, it may be stored in the registers 26 of correspondent 12a for subsequent use with the certificate ICA.
A number of variations in the generation of the certificate ICA are possible.
As shown in
Alternatively, the identification IDA may be the URL to an Online Certificate Status Protocol (OCSP) location, which may then be used as the unique subject identifier of the requestor, correspondent 12a. As a further alternative, the identification IDA may be obtained from the SubjectAltNameField of the certificate 40.
The identification information may also be obtained, as shown in
Although it may be desirable in some embodiments to use a pair of key pairs (kCA, QCA) and (k′CA, Q′CA) at the CA, the CA may use only one key pair to issue both certificates.
Similarly, the requestor 12a may have two public keys, one for the first protocol and one for the second protocol, and the CA uses the appropriate one to generate the public key BA. It can be appreciated that the same public key may be used in both protocols.
To further enhance the flexibility of provisioning the credentials, the generation of the certificate ICA may be delegated by the CA, 12c, to a second trusted CA, CA′ indicated in ghosted outline in
It will be apparent that although the use of X.509 and ECQV protocols have been exemplified, the same techniques may be applied to other combinations of certificate protocols such as RSA-ECQV where the certificates accommodate the supplementary information. Similarly, the principles may also be used with other discrete log cryptosystems and to different versions or applications of the same underlying protocol.
The principles discussed above can also be used to facilitate a public/private key upgrade as illustrated in
Turning now to
Accordingly, the above provides a method of providing credentials, the method comprising: receiving a request to issue a first credential, wherein the first credential is to conform to a first specified format; preparing the first credential; incorporating supplementary information into the first credential to permit the requestor of the first credential to utilize a second credential that conforms to a second specified format, wherein the second specified format is different from the first specified format; and issuing the first credential in conformity with the first specified format. The above also provides a certificate issued by a certification authority to authenticate a public key of a correspondent, the certificate conforming to a first specified format and including the public key and supplementary information to permit a recipient of the certificate to utilize another certificate of a second different specified format.
The above also provides a method of obtaining credentials, the method comprising: receiving a first credential according to a first specified format; and extracting supplementary information from the first credential to utilize a second credential which conforms to a second specified format, wherein the second specified format is different from the first specified format.
The above also provides a server for providing certificates in a public key cryptographic system, the server comprising a cryptographic module configured to perform cryptographic operations, the cryptographic module generating a first certificate that conforms to a first specified format; obtaining supplementary information to permit utilization of a certificate of a second specified format which is different from the first specified format; inserting said supplementary information into the first certificate; and issuing the first certificate.
The above also provides a computer readable medium comprising computer executable instructions for providing credentials from a certificate authority, the computer readable medium including instructions for: receiving a request to issue a certificate, wherein the certificate is to conform to a first specified format; preparing the certificate including a public key of a requestor; incorporating supplementary information into the certificate to permit the requestor of the certificate to utilize a certificate in conformity with a second specified format, wherein the second specified format is different from the first specified format; and issuing the certificate in conformity with the first specified format.
The above also provides a computer readable medium comprising computer executable instructions for providing credentials, the computer readable medium including instructions for: receiving a certificate issued by a certificate authority according to a first specified format; and extracting supplementary information from the certificate to utilize a second certificate of a second specified format, wherein the second specified format is different from the first specified format.
Also provided is a computing device in a cryptographic system configured for obtaining credentials, the computing device comprising a cryptographic module configured for: receiving a first credential according to a first specified format; and extracting supplementary information from the first credential to utilize a second credential which conforms to a second specified format, wherein the second specified format is different from the first specified format.
Also provided is a system for providing credentials, the system comprising: a server; and at least one computing device communicably connectable to the server over a network; wherein: the server comprises a first cryptographic module to perform cryptographic operations, the first cryptographic module being configured for generating a first certificate conforming to a first specified format and obtaining supplementary information to permit utilization of a certificate of a second specified format which is different from the first specified format, and being configured for inserting the supplementary information into the first certificate and issuing the first certificate; and wherein: each the at least one computing device comprises a second cryptographic module to perform cryptographic operations, the second cryptographic module being configured for receiving the first certificate issued by a certificate authority according to the first specified format, and being configured for extracting supplementary information from the first certificate to utilize a second certificate of the second specified format, wherein the second specified format is different from the first specified format.
Although the above principles have been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art as outlined in the claims appended hereto. The entire disclosures of all references recited above are incorporated herein by reference.
This application claims priority to U.S. Provisional Application No. 61/240,877 filed on Sep. 9, 2009, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61240877 | Sep 2009 | US |
