Biometrically enhanced digital certificates and system and method for making and using

[0001] The security and integrity of information systems depends in part on authentication of individual usersaccurately and reliably confirming or authenticating the identity of a user attempting to use the system. Once a user is authenticated, a system is then able to authorize the user to retrieve certain information or perform certain actions appropriate to the system's understanding of the user's identity. Examples of such actions include downloading a document, completing a financial transaction, or digitally signing a purchase.

[0002] Numerous methods have been developed for authenticating users. Generally, as will be understood by those skilled in the art, authentication methods are grouped into three categories, also called authentication factors, see for example Smith, Richard E., Authentication: from Passwords to Public Keys Addison-Wesley, 2002, p. 29, incorporated herein by reference in its entirety. The three categories are generally: 1) something you knowa secret such as a password or a PIN or other information; 2) something you havesuch as a smartcard, the key to a mechanical lock, an ID badge, or other physical object; and 3) something you area measure of a person such as a fingerprint or voiceprint. Each method has advantages and disadvantages including those relating to ways that a system may be fooled into accepting a normally unauthorized user in cases where, for example, a password has been guessed or a key has been stolen.

[0003] The third category abovereferred to herein as something you are authentication methodsare the subject of the biometrics field. Biometric identification is used to verify the identity of a person by measuring selected features of some physical characteristic and comparing those measurements with those filed for the person in a reference database or stored in a token (such as a smartcard) carried by the person. Physical characteristics that are used today include fingerprints, voiceprints, hand geometry, the pattern of blood vessels on the wrist or on the retina of the eye, the topography of the iris of the eye, facial patterns, and the dynamics of writing a signature or typing on a keyboard. Biometric identification methods are widely used today for securing physical access to buildings and securing data networks and personal computers.

[0004] The security and integrity of information systems also depend on keeping data confidential so that only authorized users may see or act against the data, and assuring the integrity of data so that the data cannot be changed or tampered with undetected. The field of cryptography provides tools for assuring confidentiality and integrity using encryption techniques such as ciphers and hash algorithms.

[0005] One widely known and implemented body of these tools, and procedures and practices for their use, is called Public Key Infrastructure (PKI). PKI gets its name from its use of a class of cryptographic algorithm called a public key algorithm. As is widely known to those versed in the cryptographic field, a public key algorithm is a cryptographic algorithm that operates using two different but mathematically-related keys, a public key that may be shared with any party and a private key which must be kept secret, such that (for must such algorithms) data encrypted with the public key may only be decrypted with the private key, and vice-versa. PKI standards are well known, X.509 for example, described in Housley, R., Internet X.509 Public Key Infrastructure Certificate and CRL Profile, RFC 2459, January 1999, and ITU-T Recommendation X.509 (1997 E): Information TechnologyOpen System InterconnectionThe Directory: Authentication Framework, June 1997, both of which are hereby incorporated by reference.

[0006] These standards provide powerful mechanisms for safe and private storage and transmission of confidential data so that it remains hidden from unauthorized parties. The standards provide for digital signatures, which provide the receiving party of some data with an assurance of the identity of the transmitting party. PKI standards further provide for digital certificates, which provide a tamper-resistant, portable record of the association of a public key with a person's or organization's name, attested to and signed by a trusted party, thus presenting a form of unique, irrefutable digital identity or credential for that person or organization. PKI standards also provide other useful and powerful mechanisms that can contribute to the security and integrity of information systems. On example of a certificate for use in a PKI system is an X.509 certificate.

[0007] FIG. 1 schematically depicts a standard X.509 certificate 101, herein referred to as an identity certificate, containing fields for Version 102, Certificate Serial Number 103, Signature Algorithm Identifier 104, Issuer Name 105, Validity Period 106, Subject Name 107, Subject Public Key Info 108, Issuer Unique Identifier 109, and Subject Unique Identifier 110. This general structure is known in the art. Contents of the certificate are signed by the issuing certificate authority (CA), and the signature is found in the CA Signature field 112. This figure is for reference and is not intended to provide a complete or authoritative definition of the structure or contents of an X.509 certificate.

[0008] PKI is widely used in commercial and non-commercial systems, both over the Internet and in more closed or local applications. Most web browsers, for example, use PKI and PKI-based standards to interoperate with web servers when high security is desired, as when a user specifies a credit card number for payment while placing an online order. The proliferation of electronic commerce has led many jurisdictions around the world to begin to develop legal standards with the intended result that a correctly constituted digital signature would be every bit as legally binding as a handwritten signature is today.

[0009] PKI provides powerful mechanisms, but it has weaknesses. In practice, digital certificates are issued to persons or organizations by a Certificate Authority (CA), usually a trusted third party in the business of providing a measured degree of assurance that the digital identity embodied in the certificate is valid and genuine. With such an assurance, a party may be confident that someone who claims a certain identity and presents a digital certificate is in fact that person or organization and not an impostor.

[0010] The assurance of a third-party Certificate Authority can be compromised, as it is based on assumptions that may turn out to be invalid. For example, if a CA issues a certificate to an imposter, that would invalidate the assumption that the CA has successfully and correctly verified the party to whom it is issuing the certificate. Often, certificates refer to a person by name, and may include other information such as an address. One's name has a meaning by social convention and in legal terms, but a name is not an intrinsic property of a physical person. Persons can assume names or change names, for example, creating a vulnerability in certificates utilizing names. Nor are names guaranteed to be unique; many people have names that are the same as those of other people. Linking a digital identity of a party to a name, address, or other ambiguous, extrinsic, or easily assumed or changed attribute of the party can present opportunities for impostors in PKI systems.

[0011] Another way for digital identities to be compromised is for an impostor to somehow get a copy of the private key that is associated with the public key embedded in a certificate, thus invalidating an assumption that only the person or organization to which the certificate is issued has access to the (secret) private key. Anyone with both the certificate (which is meant to be public information, freely exchanged with anyone) and the associated private key (which is meant to be secret) can impersonate someone else and compromise the security and integrity of an information system dependent on the valid use of a certificate and associated private key.

[0012] Most systems, therefore, secure the private key such that the user must authenticate before the private key can be used for any task. Many such systems require a password (something you know) or a smartcard (something you have) or both. Some systems provide additional security by putting the private key on a smartcard that is resistant to tampering or copying. However, smart cards may be lost, damaged, or stolen. Passwords may be forgotten or guessed. These concerns are part of what is called in the field the last-meter problem, the problem of making sure that an otherwise secure system isn't compromised by a failure to correctly authenticate the person using (and usually physically adjacent to) some part of the system. The last-meter problem can present opportunities for impostors in PKI systems.

[0013] Accordingly, there is a need in the art for a system offering improved security for the certification process. Such a system would preferably be compatible with PKI systems.

[0014] In a first aspect, the present invention provides a digital certificate for use in a public key infrastructure, said certificate comprising a public key field comprising a public key; and a biometric certificate field comprising biometric data; wherein said public key and said biometric data are associated with a same entity.

[0015] In some embodiments, said biometric data comprises processed biometric data. The processed biometric data may include a biometric template. Alternatively, or in addition, said biometric data may comprise a hash value in some embodiments of the invention.

[0016] In other embodiments, said biometric data comprises a raw biometric data sample.

[0017] In one embodiment, said certificate is an X.509 certificate comprising private extensions, wherein said private extensions comprise said biometric information. In one embodiment, said biometric information comprises a biometric template. In other embodiments, said biometric information comprises a hash value.

[0018] In another embodiment, said certificate is an X.509 certificate associated with an X.509attribute certificate containing said biometric information. In one embodiment, said biometric information comprises a biometric template. In other embodiments, said biometric information comprises a hash value.

[0019] In some embodiments, said biometric data is based on a biometric data sample. The biometric data sample may comprise a fingerprint scan, a facial image, an iris scan, a voice recording, or combinations thereof.

[0020] In another aspect of the present invention, a method is provided for generating a biometrically enhanced certificate comprising obtaining a biometric data sample, processing said biometric data sample to yield processed biometric information, generating biometric certificate fields utilizing said compressed biometric information, and submitting certificate information including said biometric certificate fields to at least one third-party authority.

[0021] Some embodiments of the method further comprise generating a public/private key pair. Other embodiments further comprise receiving a signed certificate.

[0022] In some embodiments, processing a biometric data sample comprises applying a hash function to said biometric data sample and said processed biometric data comprises a hash value. In other embodiments, said processing comprises extracting a biometric template from said biometric data sample. In still other embodiments, said processing further comprises encrypting said biometric template with said public key.

[0023] In some embodiments, generating biometric certificate fields comprises generating private extensions for an X.509 identity certificate, wherein said private extensions comprise processed biometric data. In other embodiments, said generating biometric certificate fields comprises generating an attribute certificate corresponding to an X.509 base certificate, wherein said attribute certificate comprises processed biometric data.

[0024] In still more embodiments, the certificate provided by the method is a digital biometrically enhanced certificate comprising a public key field comprising a public key, a biometric certificate field comprising scan sampled biometric data including processed biometric data, a biometric template, and a hash value; wherein said public key and said biometric data are associated with a same entity, said certificate is an X.509 certificate comprising private extensions, said private extensions comprise said biometric information, and said biometric data sample comprises a biometric data sample selected from the group consisting of a fingerprint scan, a facial image, an iris scan, a retinal scan, a voice recording, a DNA sample, a saliva sample, and combinations thereof.

[0025] In yet another aspect of the present invention, a computer program product for use in conjunction with a computer system having at least one processor and a memory coupled to the processor is provided, the computer program product comprising a computer readable storage medium and a computer program mechanism embedded therein, the computer program mechanism, comprising a program module that directs the computer to function in a specified manner to generate a biometrically enhanced certificate, the program module including instructions for obtaining a biometric data sample, processing said biometric data sample to yield processed biometric information, generating biometric certificate fields utilizing said compressed biometric information, submitting certificate information including said biometric certificate fields to at least one third-party authority, and receiving a signed certificate.

[0026] In some embodiments, the program module further includes instructions for generating a public/private key pair.

[0027] In other embodiments, the program module further includes instructions for applying a hash function to said biometric data sample and said processed biometric data comprises a hash value. In still other embodiments, the program module further includes instructions for extracting a biometric template from said biometric data sample. In yet other embodiments, the program module further including instructions for encrypting said biometric template with said public key.

[0028] In some embodiments, the instructions for generating biometric certificate fields comprise instructions for generating private extensions for an X.509 base certificate, wherein said private extensions comprise processed biometric data. In other embodiments, said instructions for generating biometric certificate fields comprise instructions for generating an attribute certificate corresponding to an X.509 base certificate, wherein said attribute certificate comprises processed biometric data.

[0029] In yet another aspect of the present invention, a digital certificate for use in a public key infrastructure is provided, said certificate comprising a public key field comprising a public key, a biometric certificate field comprising scan sampled biometric data including processed biometric data, a biometric template, and a hash value, wherein said public key and said biometric data are associated with a same entity, said certificate is an X.509 certificate comprising private extensions, and wherein said private extensions comprise said biometric information, and said biometric data sample comprises a biometric data sample selected from the group consisting of a fingerprint scan, a facial image, an iris scan, a retinal scan, a voice recording, a DNA sample, a saliva sample, and combinations thereof.

[0030] The present invention may be better understood, and its features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

[0031] FIG. 1 is a schematic depiction of a general structure for an embodiment of a standard X.509 certificate.

[0032] FIG. 2 is a schematic depiction of an embodiment of a biometrically enhanced certificate according to the present invention comprising an X.509 identity certificate having private extensions comprising biometric certificate fields.

[0033] FIG. 3 is a schematic depiction of an embodiment of a biometrically enhanced certificate according to the present invention comprising an X.509 attribute certificate.

[0034] FIG. 4 is a schematic overview of a method for creating a biometrically enhanced certificate, according to an embodiment of the present invention.

[0035] FIG. 5 is a schematic illustration of a method for creating a biometrically enhanced certificate embodied as an X.509 identity certificate comprising private extensions comprising biometric certificate fields, according to an embodiment of the present invention.

[0036] FIG. 6 is a schematic illustration of a method for creating a biometrically enhanced certificate comprising an X.509 attribute certificate, according to an embodiment of the present invention.

[0037] The present invention provides certificates or other data structure or data item for use in public key infrastructures. It also provides methods for making and using such certificates as well as computer program and computer program product for making and using such certificates.

[0038] By public key infrastructure (PKI), herein is meant generally any security system employing public key algorithmswith X.509 being one specific embodiment of a PKI. Public key algorithms, as used herein, generally refers to any algorithm utilizing a public-private key pair wherein two keys are stored in separate locations. That is, generally, in a transaction involving a receiving party and a transmitting party, a private key is known to the transmitting party but not the receiving party, while a public key is known to both parties. By key herein is meant datatypically in the form of a code, or string of digitsutilized in a cryptographic procedure. Thus, some embodiments of the present invention are intended for use in a PKI system where a private key (known only to a transmitting party), is utilized to encrypt a message, and a corresponding public key (known to both parties), is utilized to decrypt the message. In other embodiments, a private key is used to decrypt while a public key is used to encrypt a message.

[0039] Briefly, the present invention utilizes a combination of biometrics and PKI to address the known weaknesses of existing authentication systems, bridging the last meter between secured systems and their users. Accordingly, the present invention provides biometrically enhanced certificates or other data structure or data item containing biometric information, by adding fields containing biometric information derived from a user to a conventional Public Key Certificate (also referred to herein as an ID Certificate or Identity Certificate). Requirements for a suitable identity certificate are generally only that the identity certificate contain a public key usable in a public key infrastructure. The identity certificate generally links a key pair with an identityfor example, a name, address, corporate identification, organization identifier, or the like. Other fields in an identity certificate will be determined by the particular protocol and system used. One example of an embodiment of an X.509 identity certificate is shown in FIG. 1 and is discussed above. A biometrically enhanced certificate, therefore, provides a digital identity that is superior to a typical digital certificate because it binds a public key not just to a name, but to a physical property or properties of the person who is the subject of the certificate.

[0040] Biometrically enhanced certificates, then, comprise biometric information derived or obtained from a raw biometric data sample. A raw biometric data sample refers to a set of data generated by a sampling event or other acquisition. The type and structure of a raw biometric data sample will generally be dependent on the type of biometric sensor or acquisition device used to take the biometric data sample, and the data collection mechanisms. Suitable raw biometric data samples include fingerprint scans, voice samples, facial images, signature images, iris scans, and retinal scans. Generally, any dataset that provides a unique who you are measure of a user can be usedincluding all or portions of a genetic sequence, for example. A wide array of technologies are available to provide biometric data verification including fingerprint, voice, face, signature, iris, retina verification, and other biometric technologies.

[0041] In some embodiments of the invention, more than one kind of biometric within one biometrically enhanced certificate (a fingerprint scan as well as a voice sample, for example) is sampled. In embodiments where a plurality of biometrics are sampled (either two types of biometric, or two samples of a same biometric, such as two fingerprint scans), a plurality of biometric certificate fields may be generated, as described further below. Further, biometric fields may be combined with conventional fields containing biographical information such as name, address, and the like.

[0042] In embodiments of the present invention, a raw biometric data sample itself may be utilized in a biometric certificate field. However, it is undesirable to make a biometric data sample publicor to allow insecure access, or increase a risk of insecure access, to a biometric data sample. Accordingly, biometric data samples can be processed, yielding processed biometric information, or processed biometric data, as used herein. This processed biometric data may also referred to in the art as a biometric template, discussed further below.

[0043] Processed biometric information generally refers to biometric data derived from one or more raw biometric data samples. In one embodiment, processed biometric information is generally more compact than a raw biometric data sample. In other embodiments, processed biometric information refers to a unique identifier of a biometric data sample that cannot be utilized to reconstruct the biometric data sample. In still other embodiments, processed biometric information is both more compact than the original sample and uniquely identifies the sample while it cannot be used to reconstruct the sample. In other embodiments, processed biometric information is encrypted raw biometric data.

[0044] Accordingly, in preferred embodiments of the present invention, processed biometric information utilized in a biometric certificate field includes a biometric template, which generally refers to a distillation of unique characteristics of a biometric data sample, produced by a known biometric algorithm. For example, a fingerprint template may contain a list of minutiae points detected in a fingerprint image. Other template-generating algorithms are known in the art for fingerprint templates, and for other biometrics, as is described, for example, in A. K. Jain, L. Hong, S. Pankanti and R. Bolle, An Identity Authentication System Using Fingerprints, Proc. IEEE Vol. 85, No. 9, pp. 1365-1388, 1997; and D. Maio, D. Maltoni, Direct Gray-scale Minutiae Detection in Fingerprints,IEEE Trans. On Pattern Analysis and Machine Intelligence, Vol. 19, No. 1, pp. 27-40, 1997, both of which are hereby incorporated by reference. Templates are advantageously but optionally encryptedusing either a public or private keyprior to their inclusion in a biometrically enhanced certificate. In some embodiments, the biometric template is encrypted with the user's public key and put in a certificate Encrypted Template field. Since an encrypted template field is encrypted with the user's public key, it can only be decrypted with the user's corresponding private key, thus making it only accessible by or on behalf of the user. In other embodiments, a biometric template is encrypted with a trusted server's public key and put in a certificate's Encrypted Template field. Since this field is encrypted with the server's public key, it can only be decrypted with the server's corresponding private key, thus making it only accessible by the trusted server. In another embodiment, two biometric certificate fields are created from one raw biometric data sampleone comprising a biometric template encrypted with a user's public key, and another comprising a biometric template encrypted with a server's public key.

[0045] In other preferred embodiments of the present invention, processed biometric information utilized in a biometric certificate field include a hash value, computed by a hash function. In these embodiments, a biometric sample is acquired and processed by a hash function such as MD5, discussed in Rivest, R., The MD5 Message-Digest Algorithm, RFC 1321, April 1992, hereby incorporated by reference, or SHA-1, defined in Secure Hash Standard, Federal Information Processing Standards Publication 180-1, April 1995, hereby incorporated by reference. The hash function computes a hash value of the user's biometric sample, which is put in the certificate's Biometric Hash Value field. A preferred embodiment utilizes SHA-1 to compute biometric hash values. In preferred embodiments, the original, raw, biometric data sample is stored in a secure reference database, but this is not required.

[0046] A hash value cannot be utilized to reconstruct the original biometric data sample, but is unique to the sample; therefore, the hash value can be made public, such as by embedding within a digital certificate. If a biometric sample is successfully matched against the original biometric sample stored in a secure reference database, and the hash value of this original sample is identical with the value of this field, it is proven that the biometrically enhanced certificate was indeed created for that user. That is, in order to later prove (as in the case of repudiation of a transaction, described further below), that a particular biometric data sample was in fact utilized to generate a certain biometrically enhanced certificate, a hash value for that biometric data sample is generated and compared with the hash value contained in the biometrically enhanced certificate. The hash values will match if the biometric data sample in question was used in preparation of the biometrically enhanced certificate. Matching a subsequent biometric data sample taken from a user to the stored biometric sample utilized to generate the biometrically enhanced certificate verifies that the biometrically enhanced certificate was created for the user whose subsequent biometric data sample was taken.

[0047] Other embodiments of the invention provide biometrically enhanced certificates comprising a hash value and a biometric template.

[0048] Further, it is desirable for servers (or other devices receiving a biometrically enhanced certificate) to receive an indication of a trust level for an original enrollment of biometric data. Under certain circumstances, it may be possible for imposters during enrollment to substitute their own biometric data for that of the certificate's intended owner, thereby causing a breach in the integrity of the biometrically enhanced certificate. Therefore, it is advantageous for embodiments of the present invention to provide biometrically enhanced certificates with an optional enrollment field providing an indication of the trustworthiness of a particular enrollment process. That is, biometric data that was enrolled in a less secure manner will generally receive a lower trust level, while more secure enrollment procedures will receive a higher trust level. The enrollment field, then, allows recipients of the biometrically enhanced certificate to allow access or authenticate users based on not only a biometric data match, but also a biometric data match made at or above a certain trust level. While ascertaining and acting on a trust level in an enrollment process is discussed here, related methods and systems for determining confidence or trust levels in a transaction are discussed in U.S. application Ser. No. 10/___,___, filed ______, entitled Method And System For Determining Confidence in a Digital Transaction (Attorney Docket No. A-70779/RMA/JML), hereby incorporated by reference.

[0049] Accordingly, enrollment field, as used herein, refers to a certificate field containing information on how a user was enrolled. A measure of the overall reliability and trustworthiness of the biometrically enhanced certificate is provided by the enrollment method. Hence to be able to judge the trustworthiness of the biometrically enhanced certificate, an enrollment field contains information on how the user was enrolled. The enrollment method is generally represented as a symbolic value within the field corresponding to the actual enrollment method used. The following is a subset of possible enrollment methods:

[0050] Self-enrollment. A user enrolls using a computer which is wireline connected to the Internet, or with his wireless device (such as a personal digital assistant (PDA) or cellular phone) with a wireless Internet connection or wireless PC connection, such as 802.11. This represents the least secure method of this subset, and would receive the lowesttrust value.

[0051] Self-enrollment using an enrollment secret. In this case, as above, a user enrolls using a device connected via a wireline or wireless Internet or PC connection to the Internet. However, in order to successfully complete the enrollment process the user has received a secret (e.g. a PIN, password, or other secret information) from a trusted source (for example from the user's bank) over a different channel (for example, via postal mail, e-mail, or the like). This is a basic method of enrollment for ensuring a level of trust and confirms the enrollment secret was received. Accordingly, this secret enrollment method would receive a higher trust level than basic self-enrollment above, but a lower trust level than methods in this subset discussed below.

[0052] Self-enrollment using smart cards or SIM cards. In this case, as above, a user enrolls using a device connected via a wireline or wireless Internet or PC connection to the Internet or server device. However, in this case a pre-configured smart card or SIM card is used to establish additional trust in the enrollment process and the data provided by the user. Accordingly, this smart card method would receive a higher level of trust than methods in the subset discussed above, but a lower level than methods discussed below. The smart card or SIM card may advantageously comprise a write-only memory where the required enrollment data is stored, increasing the trust level of this method.

[0053] Face-to-face enrollment. In this method, enrollment is performed by a trusted human representative such as an employee in a bank branch, notary public, government official, or other trusted person. The user's documentation is reviewed and verified. This is the strongest level of trust presented in this subset, and would receive the highest trust value of the subset.

[0054] Specific trust level values depend on the system deployed. In some cases, it may be advantageous to have one or more enrollment methods receive the same trust leveleven if one is theoretically more or less secure than another. For example, in one embodiment, a smart card enrollment process, a secret enrollment process, and a basic self-enrollment process receive a first base trust level, and face-to-face enrollment receives a higher trust level. In this manner, a system can support many enrollment procedures, but a simplified trust tier. In other embodiments, a higher trust level may be given to enrollment processes which are theoretically less secure than those given a lower trust levelfor example if an institution wants to encourage use of a particular enrollment process despite its lower security level.

[0055] Specific embodiments of biometrically enhanced certificates are discussed below with regard to an X.509 standard. The X.509 standard is utilized here to illustrate and exemplify the invention, and is not intended to limit the practice of the invention to a single protocol.

[0056] A preferred embodiment of a biometrically enhanced certificate builds on X.509 digital certificates (see Housley, R., Internet X.509 Public Key Infrastructure Certificate and CRL Profile, RFC 2459, January 1999, and ITU-T Recommendation X.509 (1997 E): Information TechnologyOpen Systems InterconnectionThe Directory: Authentication Framework, June 1997, both of which are hereby incorporated by reference), and can be understood generally as having two components: (1) standard fields of an X.509 Identity Certificate or Attribute Certificate depending on the chosen method of implementation; and (2) additional biometric certificate fields which link the certificate to its human referent by the biometric information contained in those fields.

[0057] The implementation of additional biometric-related information can take the form of X.509 private extensions, or an X.509 Attribute Certificate. In other embodiments where X.509 is not the chosen PKI system, biometric-related information would be added to the certificate in a manner compatible with the chosen PKI system.

[0058] A standard X.509 certificate, or identity certificate, is discussed above with reference to FIG. 1. It is noted that FIG. 1 represents one embodiment of an identity certificate including some optional fields. In some embodiments, not all fields shown in FIG. 1 are present in the identity certificate. In other embodiments, other fields not shown in FIG. 1 are present. biometrically enhanced certificates according to preferred X.509 embodiments of the present invention generally fall into two groups: X.509 certificates with private extensions and X.509certificates with attribute certificates. These groups are intended to demonstrate two potential embodiments of the present invention. Those skilled in the art will readily recognize that biometric data may similarly be incorporated into certificates according to other protocols. Further, in some cases a certificate may have attributes of both the groups described below that is comprise both private extensions and attribute certificates.

[0059] Accordingly, one embodiment of the present invention provides biometrically enhanced certificates comprising an X.509 certificate with private extensions. The ability to add data elements to an X.509 certificate is described in ITU-T Recommendation X.509 (1997E): Information TechnologyOpen Systems InterconnectionThe Directory: Authentication Framework, June 1997, incorporated herein by reference. These added data elements, called private extensions, can be identified as critical or non-critical depending on whether applications are required to work with the extensions or if they may be allowed to ignore the extensions. In some preferred embodiments of the present invention, biometric certificate fields are identified as critical. In other preferred embodiments, some or all biometric certificate fields are identified as non-critical.

[0060] FIG. 2 depicts a schematic illustration of biometrically enhanced certificate 113 that comprises private extensions 111 that add biometric information to a standard X.509 identity certificate. For example, private extensions 111 may include biometric hash value field 115, one or more encrypted biometric template fields, such as encrypted template fields 116 and 117 (where template field 116 comprises template data encrypted with a user's public key, and template field 117 comprises template data encrypted with a server's public key, as discussed above), and an enrollment type field 118, which indicates a trust level for the enrollment of biometric information. Hash values templates, and enrollment types are discussed further above. The collection of biometric certificate fields shown in FIG. 2 is one embodiment of such a collection of fields. Some or all of the fields may be unnecessary in other embodiments. The biometric related fields added as private extensions may be marked as critical or non-critical depending on the specific requirements envisaged for a biometrically enhanced certificate system. In a preferred embodiment, all fields containing biometric information (either the raw biometric data or the biometric template) are identified as critical.

[0061] In another embodiment of the present invention, biometric information is provided as an X.509 attribute certificate. As defined in the relevant standards, an Attribute Certificate is very similar to a standard identity certificate with the main difference that an Attribute Certificate does not include the public key of the owner (as identity certificates do). Instead, an Attribute Certificate is uniquely linked to an identity certificate, which is then referred to as a base certificate. In addition, an Attribute Certificate is signed by an Attribute Authority that does not need to be the same entity as the Certificate Authority that signed the base certificate. FIG. 3 schematically depicts Attribute Certificate 114 containing biometric related fieldssuch as biometric hash value field 115, encrypted template fields 116 and 117, and enrollment field 118. Attribute certificate 114 further may include a variety of other fieldsincluding version field 102, holder field 123, certificate issuer field 105, algorithm identifier field 104, and certificate serial number field 103. FIG. 3 also depicts base certificate 101 with which Attribute Certificate 114 is associated. The base and attribute certificates are associated through one or more fields. In a preferred embodiment the base and attribute certificates are associated, as defined in X.509, by the attribute certificate's Holder field 123 which contains either the issuer and serial number 103 or entity name 107 of the base certificate 101, or both.

[0062] In some embodiments, a single biometrically enhanced certificate represents a plurality of identities, or users. That is, a single biometrically enhanced certificate may include biometric data associated with more than one person or entity. In these embodiments biometric fields 115-118 are repeated for each shared owner of the biometrically enhanced certificate, as appropriate. An additional Number field may be included indicating the number of shared owners.

[0063] A biometrically enhanced certificate may have, but is not required to have, all fields discussed above. Additionally, those skilled in the art will readily identify other potential field types containing biometric data. Any one or more of the above described fields added to a certificate constitutes a biometrically enhanced certificate.

[0064] The present invention further provides methods for creating biometrically enhanced certificates. The methods are generally similar to those for creating a normal digital certificate with additional steps for acquiring and handling biometric information. The specific process is dependent on the chosen implementation of the biometrically enhanced certificate, such as X.509.

[0065] FIG. 4 generally depicts methods for creating biometrically enhanced certificates as provided by embodiments of the present invention. Briefly, the fields for a standard identity certificate are generated in step 500. As discussed above, an identity certificate is generally any certificate suitable for use in a PKI system, and comprises a public key. Accordingly, identity certificate 500 comprises standard certificate fields 510 and a public key field 520. A raw biometric data sample is obtained in step 530. As discussed above, the biometric data sample is obtained through any of a wide variety of biometric sensorsincluding a fingerprint sensor, a camera for facial imaging, a microphone for voice records, etc. In some embodiments, all or portions of the raw biometric data are included in a biometric certificate field. The raw biometric data sample may then processed for use in a biometric certificate field. In preferred embodiments, the processing comprises hashing the sample, as in step 540, or extracting one or more biometric templates, as in step 550. As discussed above, in some embodiments of the present invention a hash function is used to process the data sample and one or more templates are extracted from the sample. Further, in some embodiments, a plurality of samples are obtained and processed.

[0066] Biometric templates may then be encrypted for use in a biometric certificate field, in step 560. Preferred embodiments of this encrypting step utilize public key 520 to encrypt the biometric template. In other embodiments, a different key or procedure is used to encrypt the biometric template. Further, a template may be encrypted a plurality of timeseach with a different keyfor use in a plurality of biometric certificate fields. The hashed biometric is then included in hashed biometric certificate field 570. An encrypted template is included in encrypted biometric template certificate field 580. Other extensions 590 may be included in final biometrically enhanced certificate 595.

[0067] In one embodiment, a method for creating a biometrically enhanced certificate embodied as an X.509 Certificate with Private Extensions is provided. Such a method is schematically illustrated in FIG. 5. An enrollment station 119, such as a PDA, mobile phone, personal computer, or other computing device with an associated biometric sensor, such as a microphone or fingerprint sensor, executes a program which collects a raw biometric data sample in step 200. For example, in this step, a potential user may swipe a finger across a fingerprint sensor, have an image of the user's face recorded, or the like, as discussed above.

[0068] The raw biometric data sample is then processed with a biometric algorithm specific to the type of biometric sensor used and a biometric template is generated in step 201. In a preferred embodiment, the sensor is a fingerprint sensor and the algorithm is a fingerprint minutiae extraction algorithm. Alternatively or in addition, a hash function could be applied to the biometric data sample in step 201, generating a has value for use in a biometric certificate field.

[0069] In step 202, the program collects any required additional user information such as user name, for entry into field 107 of identity certificate 101. In other embodiments, further user information may be collected at this step. In still other embodiments, step 202 is not required if no further information is needed. A public/private key pair is generated in step 203. In a preferred embodiment, the key pair is generated using the RSA public-key cipher, defined in U.S. Pat. No. 4,405,829 Cryptographic Communications System and Method (RSA), hereby incorporated by reference, but others methods such as elliptic curve ciphers may also be used, such as is set forth in Menezes, A., Elliptic Curve Public Key Cryptosystems, Kluwer Academic Publishers, 1993, hereby incorporated by reference.

[0070] The biometric certificate fields (115-118) are then prepared in step 204 from one or more biometric samples and any biometric templates according to the above definitions of those fields. The collected information, including biometric and non-biometric user information, is sent in step 205 along with the generated public key to Registration Authority (RA) 120. The RA assembles the biometric and non-biometric user information into a certificate request, as known in the art. In a preferred embodiment the certificate request is in the PKCS10 format defined in Nystrom, M. and Kaliski, B., PKCS 10: Certification Request Syntax Specification Version 1.7, RFC 2986, November 2000, hereby incorporated by reference.

[0071] In step 207, RA 120 submits the certificate request to certificate authority (CA) 121 for signature. CA 121 signs the certificate in step 208 and returns an X.509 certificate with biometric fields (a biometrically enhanced certificate) having a structure generally known in the artsee, for example, ITU-T Recommendation X.509 (1997 E): Information Technology Open Systems InterconnectionThe Directory: Authentication Framework, June 1997, hereby incorporated by reference.

[0072] CA 121 returns the certificate to RA 120 in step 209. CA 121 may also store a copy of the certificate, or transmit copies to other entities, but does not do so in a preferred embodiment. RA 120 returns the certificate to the enrollment station in step 210. RA 120 may also store a copy of the certificate, or transmit copies to other entities. In a preferred embodiment, RA 120 stores the certificates in a database.

[0073] Enrollment station 119 stores the certificate with the public/private key pair, in step 211 leaving a biometrically enhanced certificate within station 119.

[0074] In other embodiments of the present invention, methods are provided for creating a biometrically enhanced certificate based on a base identity certificate and at least one attribute certificate. In the below described embodiment, it is assumed that the user already has an X.509 identity certificate and associated public/private key pair, as discussed above.

[0075] Referring to FIG. 6, which schematically depicts a process for creating a biometrically enhanced certificate comprising a base certificate and an attribute certificate, an enrollment station 119, such as a PDA, mobile phone, personal computer, or other computing device with an associated biometric sensor, such as a microphone or fingerprint sensor, executes a program, as above, which collects a biometric sample from a user in step 250.

[0076] The biometric sample is then processed with the biometric algorithm, as above, specific to the type of biometric sensor used and a biometric template is generated in step 251. In a preferred embodiment, the sensor is a fingerprint sensor and the algorithm is a fingerprint minutiae extraction algorithm.

[0077] The biometric-related fields (115-118) are then prepared in step 252 from the raw biometric sample and biometric template according to the above definitions of those fields. The type of enrollment is known by the enrollment station and is readily available for inclusion in an enrollment field. The collected biometric information is put in an attribute certificate request, an appropriately-specified data structure such as an extensible markup language (XML) structure, in step 253. Also included is the content of the Certificate Serial Number 103 and/or the Subject Name 107 fields from the user's existing base certificate. In other embodiments, other or different linking fields from the base certificate are included.

[0078] The attribute certificate request structure is signed in step 254 with the user's private key associated with the base certificate. The signed attribute certificate request is sent in step 255 to an Attribute Authority (AA) for signature. The AA signs the attribute certificate in step 256 and returns the certificate to the enrollment station in step 257. The RA may also store a copy of the certificate, or transmit copies to other entities. In a preferred embodiment, the RA stores the certificates in a database.

[0079] The enrollment station stores the certificate with the base certificate in step 258, thus completing the process of creating a biometrically enhanced certificate.

[0080] The methods, certificates, and systems of the present invention find use in a variety of applications. A first general use of biometrically enhanced certificates is that of authentication. That is, a biometrically enhanced certificate may be used to assert and prove an identity. For example, in an embodiment in which a biometrically enhanced certificate includes template 117 encrypted with the public key of a server, that server may decrypt template 117 with its private key and compare it to a template extracted from biometric sample data collected from a user requesting authentication, thus enabling that user to, for example, log in to a secure web site or other system.

[0081] In an embodiment in which a biometrically enhanced certificate includes template 116 encrypted with the public key of a user, the system may require the user to provide a password releasing his private key, which would then be used to decrypt the template for comparison to a template extracted from biometric sample data collected from the user, thus enabling a two-factor what you know and what you are authentication, which might allow a user to, for example, sign a purchase order.

[0082] Biometrically enhanced certificates may also be used for authorizationthat is, determining what a particular user is allowed to do or see. That is, a server or other device receiving a biometrically enhanced certificate may correlate the biometrically enhanced certificate information with specific information that someone sending that biometrically enhanced certificate may accessincluding, but not limited tofinancial information including bank accounts, balances, credit histories, stock information; purchase information including prices, inventories, transactions, histories; a vote; or a document request.

[0083] Biometrically enhanced certificates may further be used for non-repudiationthat is, creating a record of an activity that will not later be refuted or altered. For example, in an embodiment in which a biometrically enhanced certificate includes biometric hash value 115, the hash value of the original biometric sample or template taken at the time of enrollment and creation of the biometrically enhanced certificate may be used to prove the authenticity of a purported biometric sample when that biometric sample is compared to a biometric sample or template collected at the time of a particular transaction being repudiated, in order to prove that the person who enrolled is the same person who was authenticated for the transaction being repudiated.

[0084] The invention may advantageously implement the methods and procedures described herein on a general purpose or special purpose computing device, such as a device having a processor for executing computer program code instructions and a memory coupled to the processor for storing data and/or commands. It will be appreciated that the computing device may be a single computer or a plurality of networked computers and that the several procedures associated with implementing the methods and procedures described herein may be implemented on one or a plurality of computing devices. In some embodiments the inventive procedures and methods are implemented on standard server-client network infrastructures with the inventive features added on top of such infrastructure or compatible therewith.

[0085] The foregoing descriptions of specific embodiments and best mode of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.