Method and apparatus for witnessed authentication of electronic documents

The present invention consists of a method and apparatus for authenticating an electronic document. In one embodiment of the invention, a party wishing to digitally sign an electronic document (the "client") stores the unsigned electronic document, and the client's public and private keys, on transportable storage media such as a floppy disk. The client conveys the storage media to an authorized electronic document authenticator. An authorized electronic document authenticator is an individual or enterprise that has access to the apparatus of the present invention or that has been authorized to use the method of the present invention. The client presents identity documents to the authenticator to verify the client's identity. The client digitally signs the electronic document in the presence of the authenticator. The authenticator verifies the digital signature using the public key provided by the client. Having witnessed the client digitally signing the electronic document using the client's private key, having verified that the public key supplied to the authenticator by the client corresponds to the private key used by the client to produce the digital signature, and having verified the identity of the client using the identification documents provided by the client and/or biometric measurements taken of the client, the authenticator appends an "authenticator identification envelope" containing a certification to that effect to the electronic document. In one embodiment of the invention, the authenticator identification envelope includes digitally recorded biometric data obtained from the client. The authenticator digitally signs the resulting electronic document, creating an authenticated electronic document. The authenticator transfers the completed, authenticated electronic document onto transportable storage media and returns it to the client.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of electronic commerce, and more 
particularly to a method and apparatus for authenticating electronic 
documents. 
2. Background Art 
Well established mechanisms exist for creating legally binding written 
instruments. One such mechanism is the application of a handwritten 
signature to a written document. For certain transactions, authentication 
of a handwritten signature, for example by a licensed public official such 
as a notary, is required. Authentication of a signature by a notary 
requires a personal appearance before the notary. The notary personally 
witnesses the execution of the signature, inspects identity documents to 
verify the identity of the person executing the signature, and affixes a 
notary statement and seal to the signed document. Notarization of a 
signature provides a level of assurance that the written instrument was in 
fact executed by the person identified by the signature, and prevents 
repudiation of the signed instrument by the signer. 
Electronic, computer based methods of doing business are increasingly 
displacing traditional paper based methods. Electronic communications and 
electronic documents are replacing written contracts, orders, payment 
instruments, account statements, invoices, and other paper documents. 
Unlike their paper counterparts, electronic documents do not exist in 
physical form. Instead, they consist of sets of digital data that may be 
stored on various types of digital storage media ranging from volatile 
internal RAM memory to non-volatile ROM memory to magnetic and/or optical 
disk storage media, and that may be transmitted over various computer 
communications links including local and wide area networks, and the 
Internet. Because electronic documents do not have a physical form, the 
mechanisms devised to create legally binding paper instruments, such as 
affixing a notarized signature, cannot be used for electronic documents. 
Accordingly, a need has arisen for alternative mechanisms for creating and 
authenticating legally binding electronic documents and communications. 
Digital encryption, digital message digests, digital signatures, and 
digital certificates are some of the existing cryptographic tools that are 
used in the present invention to address this need. 
Two well known types of cryptography are secret key cryptography and public 
key cryptography. 
Secret key cryptography is a symmetric form of cryptography in which a 
single key is used to encrypt and decrypt an electronic document. To 
encrypt an electronic document, the electronic document and the secret key 
are supplied to a hardware device or a software encryption program that 
transforms the electronic document into an encrypted electronic document 
by means of an encryption process that uses the secret key and the 
electronic document as an input. The original electronic document can only 
be obtained from the encrypted electronic document by applying a reverse 
decryption process using the same secret key. Because the same secret key 
is used for encryption and decryption, both the sender and the recipient 
of the encrypted electronic document must have a copy of the secret key. 
The security of secret key cryptography can therefore be compromised by 
either the sender or the recipient. 
Public key cryptography is an asymmetric form of cryptography that uses a 
two-key pair, typically referred to as a public key and a private key. 
These two keys are different but constitute a matched key pair. In public 
key encryption, electronic documents encrypted with either the public or 
private key of a public-private key pair can only be decrypted using the 
other key of the key pair. For example, an electronic document encrypted 
with a public key can only be decrypted using the corresponding private 
key. Conversely, an electronic document encrypted with a private key can 
only be decrypted using the corresponding public key. 
The terms "public" key and "private" key stem from a manner in which public 
key cryptography is often used. A party A, concerned about privacy of its 
incoming communications generates a public-private key pair, using 
cryptographic hardware and/or software. Party A keeps its private key 
secret, but freely distributes its public key. Party B wishing to send a 
confidential electronic document to party A, can encrypt its electronic 
document using party A's freely available public key. Since the electronic 
document can then only be decrypted using the corresponding private key, 
party B can be assured that only party A, in possession of the private 
key, will be able to decode the encrypted electronic document. 
A number of uncertainties arise with respect to the use of public key 
cryptography. One uncertainty relates to the identity of the owner of the 
private key that corresponds to the public key. It is possible, for 
example, that a public key may be circulated that fraudulently purports to 
be the public key of party A, but the corresponding private key of which 
is actually held by party C. A sender who encrypts a confidential 
communication to party A, using the public key the sender believes belongs 
to party A, will instead be creating a confidential communication that can 
be decrypted and read only by party C. 
A second uncertainty, from the perspective of the recipient, relates to the 
identity of the sender of an encrypted communication. Since the 
recipient's public key is freely distributed, encryption of a 
communication with the recipient's correct public key does not provide any 
information concerning the sender, other than that the sender is someone 
who has access to the recipient's public key. As public keys are often 
freely available from public key repositories, the sender could be anyone. 
A third uncertainty concerns the integrity of the communication--that is, 
there is an uncertainty as to whether the communication received by the 
recipient is the actual communication sent by the sender. For example, the 
communication may have been intercepted, modified, or replaced. 
Digital signatures and digital certificates have been devised to address 
some of the uncertainties inherent in public key cryptography. 
One of the purposes of a digital signature is to link an electronic 
document with an owner of the private key corresponding to a particular 
public key. Additionally, a digital signature can be used to determine 
whether an electronic document has been altered during transmission of the 
document from the sender to the recipient. 
One form of digital signature uses a message digest. A message digest is a 
value that is generated when an electronic document is passed through a 
one way encryption process ("digesting process") such as a hashing 
routine. An ideal digesting process is one for which the probability that 
two different electronic documents will generate the same message digest 
is near zero. In this form of digital signature, both the sender and the 
recipient need to know which digesting process is being used. The sender 
generates the electronic document, and generates a message digest by 
passing the electronic document through the digesting process. The sender 
encrypts the resulting message digest with the sender's private key. The 
result, the encrypted message digest, then becomes the digital signature 
of the electronic document. The digital signature may be appended to the 
electronic document or kept as a separate entity. 
The recipient obtains the electronic document and the digital signature of 
the sender. The recipient decrypts the digital signature using what the 
recipient believes to be the sender's public key, obtaining the decrypted 
message digest X. The recipient processes the received electronic document 
using the digesting process, obtaining message digest Y. The recipient 
then compares message digest Y to message digest X. If X=Y, the message 
digests are the same. This verifies that the electronic document was (1) 
digitally signed by the private key corresponding to the public key used 
to recover message digest X, and (2) that the electronic document content 
was not changed from the time that it was signed to the time that the 
digital signature was verified. However, the uncertainty remains as to 
whether the public key used by the recipient to decrypt the digital 
signature, which the recipient believes is the public key of the sender, 
is in fact the sender's public key. 
The effectiveness of the digital signature, as well as other uses of public 
key cryptography, thus depends on the level of confidence as to the 
identity of the holder of the private key corresponding to a particular 
public key. 
Digital certificates are intended to provide a level of assurance as to the 
identity of the holder of the private key corresponding to a particular 
public key. The issuers of digital certificates are called certification 
authorities. A digital certificate constitutes a certification by a 
certification authority that a particular public key is the public key of 
a particular entity, and that this entity is the holder of the 
corresponding private key. 
Certification authorities are often commercial enterprises that collect 
fees for issuing digital certificates. To obtain a digital certificate, an 
applicant submits an application for a digital certificate together with 
the applicant's public key and some form of identity verification to a 
certification authority. The certification authority reviews the 
application, and if the application meets the criteria established by the 
certification authority, issues a digital certificate to the applicant. 
The digital certificate itself is an electronic document. Although a 
variety of formats exist, a digital certificate typically includes, among 
other items, the name of the certification authority, the name of the 
certificate holder, the expiration date of the certificate, the public key 
of the certificate holder, and the digital signature of the certification 
authority. The digital certificate constitutes a certification by the 
certification authority that the holder of the certificate is the owner of 
the public key specified in the certificate, and, by implication, is 
therefore the holder of the corresponding private key. 
The authenticity of a digital certificate is tested by verifying the 
certification authority's digital signature using the certification 
authority's public key. The level of assurance provided by a digital 
certificate depends on a number of factors, including the reputation of 
the certification authority issuing the certificate, the thoroughness of 
the procedures used by the certification authority in issuing the 
certificate, and the level of confidence in the certification authority's 
public key. Some certification authorities issue different levels of 
certificates, corresponding to different levels of investigation performed 
by the certificate authority during evaluation of an application. 
The authenticity of a digital signature depends largely on the authenticity 
of the public key used by a recipient to test the digital signature. A 
digital certificate may be used to help authenticate a digital signature 
by verifying the authenticity of the certificate holder's public key. The 
digital certificate may be appended to an electronic document, or the 
recipient of an electronic document may obtain a copy of the certificate 
from the issuing certification authority or other certificate repository. 
One drawback of using digital certificates for authentication of a digital 
signature is that a party wishing to digitally sign an electronic document 
must have previously applied for and obtained a digital certificate. If a 
party does not have a digital certificate its digital signature is 
questionable. A second drawback of prior art digital certificates is that 
certification authorities do not require an applicant to prove that the 
applicant has actual custody of the private key corresponding to the 
public key the applicant presents to the certification authority for 
certification at the time of application. Accordingly, the question 
remains as to the identity of the real holder of the private key 
corresponding to the public key identified in the digital certificate. 
Accordingly, there remains a need for a means for verification of the 
authenticity of a digital signature in the absence of a digital 
certificate, and for verifying that a purported owner of a public key in 
fact has present custody of the corresponding private key at the time a 
digital signature is executed. 
SUMMARY OF THE INVENTION 
The present invention consists of a method and apparatus for authenticating 
an electronic document. In one embodiment of the invention, a party 
wishing to digitally sign an electronic document (the "client") generates 
the document using appropriate software, such as, for example, a word 
processing program or a spreadsheet. The client, if not already in 
possession of a public-private key pair, generates a public-private key 
pair using cryptographic hardware and/or software. The client conveys the 
unsigned electronic document, and the client's public and private keys, to 
an authorized electronic document authenticator on storage media such as a 
floppy disk or by other electronic means. An authorized electronic 
document authenticator is an individual or enterprise that has access to 
the apparatus of the present invention or that has been authorized to use 
the method of the present invention. The client presents identity 
documents to the authenticator to verify the client's identity. Such 
identity documents may include picture identification documents such as a 
driver's license and a passport, and other identification documents. 
Depending upon the degree of identity verification required, the 
authenticator may also take fingerprint or retinal scans or other 
biometric readings of the client. 
The client digitally signs the electronic document in the presence of the 
authenticator. In one embodiment, in which the cryptographic software used 
by the client is compatible with the cryptographic software available on a 
computer system of the authenticator, the client places the storage media 
containing the electronic document to be signed, and the public and 
private keys of the client, into an appropriate storage media reading 
device of the authenticator's computer. The client, while being observed 
by the authenticator, then proceeds to digitally sign the electronic 
document by giving appropriate commands to the authenticator's computer, 
using the client's private key contained (in pass phrase protected form) 
on the client's storage media. The software in the authenticator's 
computer creates the client's digital signature of the electronic document 
by deriving a message digest of the electronic document and encrypting the 
message digest with the private key supplied by the client. 
The authenticator verifies the digital signature using the public key 
provided by the client by giving appropriate commands to the 
authenticator's computer. The software in the authenticator's computer 
decrypts the digital signature using the client's public key obtaining 
message digest X. The authenticator software derives a second message 
digest Y for the electronic document, and compares message digest Y to 
message digest X. The two message digests X and Y will be identical only 
if the private key used by the client to create the digital signature and 
the public key used by the authenticator to decrypt the digital signature 
are a valid public-private key pair. The authenticator (1) verifies the 
identity of the client using the identification documents provided by the 
client and/or biometric measurements taken of the client; (2) witnesses 
the client digitally signing the electronic document using the client's 
private key; and (3) verifies that the public key supplied to the 
authenticator by the client corresponds to the private key used by the 
client to produce the digital signature. The authenticator then creates an 
"authenticator identification envelope" containing a certification of the 
above numerated steps. In one embodiment of the invention, the 
authenticator also includes digitally recorded biometric data of the 
client in the authenticator identification envelope. The authenticator 
digitally signs the authenticator identification envelope and the 
electronic document, creating an authenticated electronic document. In one 
embodiment the authenticator gives appropriate commands to the 
authenticator's computer to store the authenticated electronic document on 
the storage media supplied by the client, and returns the storage media 
containing the authenticated electronic document to the client. 
In one embodiment, if the cryptographic software used by the client to 
produce its public-private key pair is not compatible with cryptographic 
software available on the authenticator's computer, the client brings with 
it to the authenticator either a copy of the cryptographic software used 
by the client, or a portable computer in which the cryptographic software 
used by the client has been installed. 
In one embodiment of the invention, the authenticator assists the client in 
the application process for obtaining a digital certificate from a 
certification authority. A party wishing to apply for a digital 
certificate from the certification authority fills out an application for 
a digital certificate in an appropriate electronic form. The authenticator 
authenticates the digital certificate application in the same manner used 
to authenticate other electronic documents. In this embodiment, instead of 
returning the authenticated application to the applicant, the 
authenticator may convey the authenticated application in electronic form 
to the certification authority.

DETAILED DESCRIPTION OF THE INVENTION 
A method and apparatus for authentication of electronic documents is 
described. In the following description, numerous specific details are set 
forth in order to provide a thorough description of the present invention. 
It will be apparent, however, to one skilled in the art, that the present 
invention may be practiced without these specific details. In other 
instances, well-known features have not been described in detail so as not 
to obscure the present invention. 
FIG. 1 is a schematic diagram of the topology of one embodiment of the 
present invention. As shown in FIG. 1, participants involved in this 
embodiment of the invention include an originating party or "client" 100 
and an authenticator 130. Client 100 is the party that wishes to have its 
digital signature authenticated by authenticator 130. Authenticator 130 is 
an individual or enterprise that has access to the apparatus of the 
present invention or that has been authorized to use the method of the 
present invention. In the embodiment of FIG. 1, client 100 has a client 
computer 110, which may, for example, be a personal computer running 
Microsoft Windows 95.TM.. Authenticator 130 has an authenticator computer 
140, which may, for example, be a personal computer running Microsoft 
Windows 95. FIG. 160 also shows a receiving party 160. Receiving party 160 
is an intended recipient of the electronic document to be signed by client 
100. 
FIG. 2 is a block diagram of the process used to produce an authenticated 
electronic document in one embodiment of the present invention. In the 
embodiment of FIG. 2, the process begins with client 100 generating a 
public-private key pair at block 200. The client may, for example, 
generate such a public-private key pair using cryptographic software, such 
as for example ViaCrypt PGP.TM. from ViaCrypt, running on client computer 
110. Alternatively, if the client already has a public-private key pair, 
the process may start at block 210, at which client 100 generates the 
electronic document to be digitally signed according to the present 
invention. The electronic document to be signed may be a text file, a word 
processing file, a graphics file, a data base file, a spreadsheet file, or 
any other file containing digital data. Client 100 may generate the 
electronic document at block 210 using appropriate software running on 
client computer 110. Alternatively, instead of generating the electronic 
document, client 100 may obtain the electronic document from another 
party, for example by downloading it from the Internet. 
After generating or otherwise obtaining the electronic document to be 
signed at block 210, and editing the electronic document as necessary to 
place it in final form, client 100 stores the electronic document on 
transportable storage media such as floppy disk 120 shown in FIG. 1. Any 
other form of transportable storage media, including transportable hard 
disk drives (such as, for example, Jaz.TM. hard drives), magnetic tape 
cartridges, flash RAM cards, smart cards, chip cards, recordable CD-ROM's, 
or other transportable storage media may be used. Client 100 also copies 
the client's public and private keys to the same or another transportable 
storage media. Cryptographic programs such as ViaCrypt PGP.TM. do not 
allow a private key to be stored on storage media other than in encrypted 
form. Accordingly, the private key may be stored in encrypted form on the 
transportable media. 
At block 230, client 100 conveys the transportable media on which the 
electronic document and the public and private keys have been stored to 
authenticator 130. Alternatively, instead of storing the electronic 
document and/or the client's public and private keys on transportable 
media and physically conveying the transportable media to authenticator 
130, client 100 may transmit one or more of the electronic document and 
the public/private keys to authenticator 130 by electronic means, using, 
for example, a telephone line and a modem. 
At block 240, authenticator 130 inspects identification documents provided 
by client 100 to verify the client's identity. Such documents may include 
photo identification documents such as passports and drivers licenses, as 
well as other identification documents. In addition, or as an alternative, 
the authenticator may take biometric readings of client 100 at block 250. 
For example, the authenticator may digitally record the client's 
fingerprints, may take a digital voice print of the client, may take a 
retinal scan, or take some other form of biometric reading. 
At block 260, client 100 digitally signs the electronic document in the 
presence of authenticator 130. In this embodiment, client 100 uses 
equipment of the authenticator, for example the authenticator's computer 
system, to produce the client's digital signature. To do so, the 
transportable media supplied by client 100, containing the electronic 
document to be signed and the public and private keys of client 100, is 
made accessible to the authenticator computer. If, for example, the 
transportable media consists of a floppy disk, the floppy disk is inserted 
in a floppy disk drive attached to the authenticator computer. Client 100 
then uses encryption software on the authenticator computer to produce a 
digital signature and attach it to the electronic document. In one 
embodiment of the invention, the encryption software on the authenticator 
computer includes ViaCrypt PGP/Business Edition.TM. from ViaCrypt 
("PGP/Business Edition"). FIG. 3 is an illustration of a main menu 300 
from PGP/Business Edition. As shown in FIG. 3, main menu 300 contains a 
"Sign" menu selection 310. In this embodiment, to digitally sign an 
electronic document, client 100 selects "Sign" menu selection 310 from 
main menu 300 of PGP/Business Edition. In embodiments using other 
encryption software, client 100 uses the commands appropriate to the 
particular encryption software used. 
In an embodiment using PGP/Business Edition, after client 100 selects 
"Sign" menu selection 310, a dialog box appears requesting selection of 
the file to be digitally signed. Client 100 selects the drive 
corresponding to the transportable media containing the electronic 
document to be signed, and selects the electronic document. An example 
electronic document 400 is shown in FIG. 4. As shown in FIG. 4, electronic 
document 400 consists of several lines of text 410. 
After client 100 has selected the electronic document to be signed, 
PGP/Business Edition looks for a private "keyring" of private keys that 
are available. A private "keyring" is a file containing private keys in 
encrypted form. In this embodiment, the file on the client's transportable 
media containing client 100's private key constitutes such a private 
keyring. If the private keyring found by the PGP/Business Edition contains 
several keys, PGP lists the user ID's of the available private keys and 
prompts client 100 to select the private key to be used. If the keyring 
only contains a single key, PGP/Business Edition assumes that this key is 
the one to be used to digitally sign the electronic document. 
In this embodiment, the client's private key is stored on transportable 
media in encrypted form. The encryption method used is secret key 
encryption using a client selected "pass phrase" as the source for the 
secret key. To create a digital signature using the client's private key 
the private key must be decrypted. Accordingly, after the appropriate 
private key to be used to digitally sign the electronic document has been 
identified, PGP/Business Edition prompts client 100 for the pass phrase to 
be used to decrypt client 100's private key so that it can be used to 
produce the desired digital signature. FIG. 5 illustrates a dialog box 500 
presented by PGP/Business Edition requesting entry of client 100's pass 
phrase. 
After client 100 enters the client's pass phrase for the client's private 
key, PGP/Business Edition decrypts the private key, generates a message 
digest of the electronic document, encrypts the message digest with the 
client's private key, and attaches the resulting digital signature to the 
electronic document. FIG. 6 illustrates electronic document 400 of FIG. 4 
after the digital signature of client 100 has been attached. As shown in 
FIG. 6, the digitally signed document 600 contains a beginning of signed 
message indicator 610, a copy 620 of the original document 400, a 
beginning of digital signature indicator 630, the digital signature 640, 
and an end of digital signature indicator 650. 
Referring to FIG. 2, after client 100 has completed digitally signing the 
electronic document at block 260, the authenticator verifies the client's 
digital signature using cryptographic software on the authenticator 
computer and the client's public key as supplied by client 100. In one 
embodiment, in which the cryptographic software on the authenticator 
computer includes PGP/Business Edition, the authenticator initiates 
verification of the client's digital signature by selecting the "Verify 
Signature" menu option 320 from main menu 300 shown in FIG. 3 and 
selecting the electronic document for which the digital signature is to be 
verified from a file menu. PGP/Business Edition then searches for 
available public keys. When PGP/Business Edition finds the corresponding 
public key it uses it to test the digital signature. 
Once the proper key has been identified, the cryptographic software 
verifies the digital signature. The cryptographic software generates a 
message digest of the signed electronic document, obtains a second message 
digest by decrypting the digital signature using the client's public key, 
and compares the first and second message digests. If the two message 
digests are identical, the software notifies the authenticator that the 
digital signature is good. FIG. 7 shows an example of a dialog box 700 
used by PGP/Business Edition to indicate a good digital signature. If the 
two message digests are not identical, the software notifies the 
authenticator that the digital signature is not good. FIG. 8 shows an 
example of a dialog box 800 used by PGP/Business Edition to indicate a bad 
digital signature. 
Referring to FIG. 2, if the signature is found to be bad at block 267, the 
client re-signs the electronic document at block 269, and the verification 
process repeats at block 265. If the signature is found to be good at 
block 267, the authenticator attaches an authenticator statement to the 
client-signed electronic document at block 270. 
An authenticator statement is a statement the authenticator generates by 
which the authenticator attests to having witnessed the client's digital 
signing of the electronic document. The exact wording of the authenticator 
statement may vary from one embodiment to the other, may vary according to 
the client's requirements, and/or may be dictated by law of the 
jurisdiction in which the authenticator is situated. In one embodiment of 
the invention, the authenticator statement is part of an "authenticator 
identification envelope" that is attached by the authenticator to an 
authenticated document. An authenticator identification envelope is a set 
of information that the authenticator attaches to the signed document. It 
includes the authenticator statement, and may include additional 
information. An authenticator statement may be in a human language or may 
be computer encoded. 
In the embodiment of FIG. 2, after the authenticator attaches the 
authenticator statement to the signed electronic document at block 270, 
the authenticator at block 275 optionally attaches a copy of biometric 
data for the client that was obtained by the authenticator at block 250. 
In one embodiment, the biometric data is made part of the authenticator 
identification envelope. 
At block 280, the authenticator digitally signs the electronic document, 
plus the client's digital signature, plus the information added by the 
authenticator. An example of a resulting, authenticated document is shown 
in FIG. 9. 
FIG. 9 illustrates the document of FIG. 6 after it has been authenticated 
according to one embodiment of the present invention. In the embodiment of 
FIG. 9, authenticated document 900 consists of three main sections: 
client-signed document 600, authenticator identification envelope 910, and 
authenticator signature 960. 
Client-signed document 600 consists of a copy of the original electronic 
document after it has been signed by the client, as also shown in FIG. 6. 
Authenticator identification envelope 910 comprises information added by 
the authenticator to the electronic document according to the present 
invention. In the embodiment of FIG. 9, authenticator identification 
envelope 910 includes a beginning of authenticator identification envelope 
indicator 915, a beginning of authenticator statement indicator 920, an 
authenticator statement 925, an end of authenticator statement indicator 
930, a beginning of biometric data indicator 935, biometric data 940, an 
end of biometric data indicator 945, and an end of authenticator 
identification envelope indicator 950. 
Beginning of authenticator identification envelope indicator 915 is an 
indicator that identifies the beginning of authenticator identification 
envelope 910. In the embodiment of FIG. 9, beginning of authenticator 
identification envelope indicator 915 consists of a text string. 
Beginning of authenticator statement indicator 920 is an indicator that 
identifies the beginning of authenticator statement 925. In the embodiment 
of FIG. 9, beginning of authenticator statement indicator 925 consists of 
a text string. 
Authenticator statement 925 consists of information added by the 
authenticator describing particulars of the digital signature witnessed by 
the authenticator. In the embodiment of FIG. 9, authenticator statement 
925 includes a statement 921 indicating the identity of the authenticator, 
data 922 indicating the date, time and place at which the authenticator 
witnessed the digital signing of the electronic document, and a listing 
923 of the materials examined by the authenticator to establish the 
identity of the client. In the embodiment of FIG. 9, authenticator 
statement 925 also includes a statement 924 indicating that the 
authenticator has taken biometric readings of the client, identifying the 
particular type of biometric reading taken, and indicating that resulting 
biometric data is appended to the electronic document. 
End of authenticator statement indicator 930 is an indicator that 
identifies the end of authenticator statement 925. In the embodiment of 
FIG. 9, end of authenticator statement indicator 930 consists of a text 
string. 
Beginning of biometric data indicator 935 is an indicator that identifies 
the beginning of biometric data 940. In the embodiment of FIG. 9, 
beginning of biometric data indicator 935 consists of a text string. 
Biometric data 940 consists of biometric data resulting from biometric 
readings made by the authenticator of the client. In FIG. 9, the biometric 
data is represented by several lines of digital 1's and 0's. The biometric 
data appended by an authenticator to a signed electronic document can take 
a variety of other forms. 
End of biometric data indicator 945 is an indicator that identifies the end 
of biometric data 940. In the embodiment of FIG. 9, end of biometric data 
indicator 945 consists of a text string. 
End of authenticator identification envelope indicator 950 is an indicator 
that identifies the end of authenticator identification envelope 910. In 
the embodiment of FIG. 9, end of authenticator identification envelope 
indicator 950 consists of a text string. 
In the embodiment of FIG. 9, the authenticator identification envelope 
includes an authenticator statement and biometric data. In other 
embodiments, more or less information may be included in the authenticator 
identification envelope. For example, the authenticator identification 
envelope may contain an identification level identifier that specifies the 
degree of scrutiny of the client's identity undertaken by the 
authenticator. The authenticator may also include a copy of the public key 
presented by the client, and/or a copy of a digital certificate obtained 
by the client from a certification authority authenticating the public key 
of the client. The authenticator may also include a copy of a digital 
certificate obtained by the authenticator from a certification authority 
authenticating the public key of the authenticator. In some embodiments, 
information supplied by the authenticator may be appended to an electronic 
document without using beginning and end of authenticator identification 
envelope indicators such as indicators 915 and 950, respectively, to 
delineate a specific authenticator identification envelope. The term 
"authenticator identification envelope" as used herein refers to 
information added by an authenticator to a client-signed document, 
regardless of whether or not such information is labeled with the words 
"authenticator identification envelope" and regardless of whether or not 
indicators are used to identify bounds of such added information. 
In this embodiment authenticator digital signature 960 includes a beginning 
of signed message indicator 965, digital signature indicator 961, a 
version indicator 962, an encrypted message digest 963, and an end of 
digital signature indicator 964. 
Beginning of signed message indicator 965 is an indicator that identifies 
the beginning of the component parts that are signed by the 
authenticator's digital signature. 
Beginning of digital signature indicator 961 is an indicator that 
identifies the beginning of authenticator digital signature 960. In the 
embodiment of FIG. 9, beginning of digital signature indicator 961 
consists of a text string. 
Version indicator 962 indicates the version of the software program used to 
produce authenticator digital signature 960. 
Encrypted message digest 963 is a message digest of client-signed 
electronic document 600 and authenticator identification envelope 910 
encrypted using the authenticator's public key. Encrypted message digest 
963 constitutes the authenticator digital signature of the client's 
document plus the authenticator identification envelope. 
End of digital signature indicator 964 is an indicator that identifies the 
end of authenticator digital signature 960. In the embodiment of FIG. 9, 
end of digital signature indicator 964 consists of a text string. 
Referring to FIG. 2, after signing the electronic document at block 280, 
the authenticator transfers the authenticated document (such as, for 
example, authenticated document 900 of FIG. 9) to transportable media of 
the client at block 285, which may be the same transportable media on 
which the client brought the original electronic document to the 
authenticator, or may be another transportable media, such as, for 
example, floppy disk 170 of FIG. 1. In addition, or as an alternative, to 
transferring the authenticated electronic document to transportable media, 
the authenticator may transmit the authenticated electronic document by 
electronic means 150 (such as, for example, the Internet) to the office of 
the client or to some other recipient 160 at block 290. In one embodiment, 
the authenticator encrypts any such electronic document transmitted by 
electronic means using the public key of the recipient. 
At block 295, the authenticator records transaction data concerning the 
authentication transaction in a transaction log. Such transaction data may 
include, for example, the date and time of the authentication, the name of 
the client, forms of identification used for client verification, and a 
descriptive title of the electronic document authenticated. 
One example of an electronic document that an authenticator may transmit 
electronically to a recipient at block 290 is an application for a digital 
certificate. In one application of the present invention, the 
authenticator acts as an agent for a certification authority. A client 
wishing to obtain a digital certificate from the certification authority 
in this embodiment obtains an electronic version of the certification 
authority's application form (for example from the certification 
authority's Internet server) and fills in the requested information. The 
client brings the completed electronic application to the authenticator, 
digitally signs it in the presence of the authenticator, and the 
authenticator adds an authenticator identification envelope according to 
the present invention. In this application, the authenticator 
identification envelope may contain a specific form of authenticator 
statement as required by the certification authority. The authenticator 
digitally signs the application, encrypts the authenticated application 
with the certification authority's public key, and transmits the encrypted 
application to the certification authority. In the embodiment of FIG. 2, 
the public/private keys generated by the client and the client's 
encryption software are compatible with encryption software of the 
authenticator. FIG. 10 is a block diagram of a process used to produce an 
authenticated electronic document according to the present invention in an 
embodiment in which the encryption software of the authenticator is not 
compatible with the client's public and private keys or encryption 
software. 
As shown in FIG. 10, in this embodiment, the client generates a 
public/private key pair at block 1000 and generates the electronic 
document to be authenticated at block 1005. The client takes a portable 
computer containing the client's encryption software, the electronic 
document, and the client's public/private keys to the authenticator's 
place of business at block 1010. The authenticator inspects the client's 
identification documents at block 1015, and optionally takes biometric 
readings of the client at block 1020. The client digitally signs the 
electronic document using the client's portable computer in the 
authenticator's presence at block 1025. 
The authenticator verifies the client's digital signature using the 
client's encryption software and the client's public key at blocks 1030 
and 1035. 
If the authenticator determines that the signature is not valid, the client 
re-signs the electronic document at block 1040. The process then returns 
to block 1030. 
If the authenticator determines that the signature is valid, the 
authenticator transfers the client-signed document to an authenticator's 
computer at block 1045. The authenticator may transfer the electronic 
document by establishing an electronic connection between the client 
computer and the authenticator computer and transferring the document 
electronically, or the authenticator may store the electronic document on 
transportable media and transfer the transportable media from the client 
computer to the authenticator computer. 
The authenticator uses the authenticator computer to attach an 
authenticator identification envelope of the present invention to the 
electronic document at block 1050. The authenticator identification 
envelope may contain additional information, such as an authenticator 
statement indicating that the authenticator verified the client's digital 
signature using client supplied computer and software. The authenticator 
digitally signs the electronic document at block 1055. The authenticator 
transfers the authenticated document to the client's portable computer or 
transportable media at block 1060, and/or transmits the authenticated 
document to a recipient in electronic form at block 1065. The 
authenticator records pertinent transaction data in the authenticator's 
transaction log at block 1070. 
FIG. 11 is a schematic diagram of a computer system that may be used as a 
client computer or an authenticator computer of the present invention. The 
computer system shown in FIG. 11 includes a CPU unit 1100 that includes a 
central processor, main RAM memory 1105, peripheral interfaces, 
input-output devices, power supply, and associated circuitry and devices; 
a display device 1110 which may be a cathode ray tube display, LCD 
display, gas-plasma display, or any other computer display; an input 
device 1130, which may include a keyboard, mouse, digitizer, or other 
input device; non-volatile storage 1120, which may include magnetic, 
re-writable optical, or other mass storage devices; a transportable media 
drive 1125, which may include magnetic, re-writable optical, or other 
removable, transportable media, and a printer 1150. The computer system 
may also include a network interface 1140, which may include a modem, 
allowing the computer system to communicate with other systems over a 
communications network such as the Internet. Any of a variety of other 
configurations of computer systems may also be used. In one embodiment, 
the authenticator computer comprises an Intel Pentium.TM. CPU and runs the 
Microsoft Windows 95.TM. operating environment. 
Thus, an improved method and apparatus for authentication of electronic 
documents has been described. Although the present invention has been 
described with respect to certain example embodiments, it will be apparent 
to those skilled in the art that the present invention is not limited to 
these specific embodiments. Further, although the operation of certain 
embodiments has been described in detail using specific software programs 
and certain detailed process steps, different software may be used, and 
some of the steps may be omitted or other similar steps may be 
substituted, without departing from the scope of the invention. Other 
embodiments incorporating the inventive features of the present invention 
will be apparent to those skilled in the art.