Abstract:
Methods and systems are provided for using an existing email transfer protocol, such as SMTP, to exchange digital objects in an authenticated manner. The provided methods and systems solve the bootstrapping problem of computer identities for P2P communication by authenticating the exchange of public information. If the electronic mail protocols are strong, in that sending an email message to a given address results in the message reaching that address with a high degree of confidence, then the exchange of public information performed in accordance with embodiments of the invention is confidently authenticated.

Description:
FIELD OF THE INVENTION 
   This invention pertains generally to the field of information security and more specifically to authentication protocols. 
   BACKGROUND OF THE INVENTION 
   A common form of communications between computers connected to the Internet follows a paradigm known in the industry as client-server. For example, existing servers are email servers, web servers, file servers, online banking servers, etc. Clients include home personal computers, office personal computers, laptop computers, hand-held devices, wireless digital telephones, etc. The various client devices connect and interact with the various server devices. In this model the different servers employ their own ways of authenticating and authorizing the client devices that connect with them. For example, some email servers issue and use pre-registered identities to authenticate and authorize. Some banking organizations use their own member identification and password databases to do the authentication and authorization. So a given client device, say a personal computer at home, needs to conform to the differing authentication methods enforced by the different servers with which it connects and interacts. In the client-server model, the broad problem of how two interacting computers “recognize” one another currently is solved by making the server computer enforce its preferences unilaterally on the client computer. 
   Although the above-described model works well for client-server interaction, it becomes impractical for interactions between the various client machines themselves. The industry terminology for such interaction between various client devices is called peer-to-peer (P2P) communications. In this case, neither client computer can force its authentication preferences on the other. For example, consider the desire for a first user, Alice, to share and exchange videos and pictures from her personal computer with a second user, Bob, who also has a personal computer. Bob may wish to authenticate Alice, in order to be confident that the videos and pictures are indeed being sent by her, rather than being sent by an imposter. 
   Additionally, Alice may wish to transmit the videos and pictures securely using an encryption technique such as RSA, so that an eavesdropper cannot view the videos or pictures. RSA is a public-key cryptography technique whereby anyone can encrypt data for a given user with the user&#39;s public-key, but only the user can decrypt the data by using the corresponding private-key. Thus, Alice and Bob need to first exchange their respective public-keys in order to establish the secure channel per the RSA algorithm. Exchanging public-keys is not a trivial task. Charlie, a malicious hacker, could try to “sit in the middle” of the key exchange communication. Charlie sends his own public-key to Alice, but pretending to be Bob; he sends his own public-key to Bob, but pretending to be Alice. Given that this initial key exchange communication is itself not secure, there is no simple way for Alice and Bob to realize that Charlie is “in the middle”. If they fall for Charlie&#39;s ploy and start communicating using his key, he can act as the middle-man and pass all the communications between Alice and Bob, but be able to eavesdrop on all the content being passed back and forth. And of course he can make this even worse by changing the passed content as well. 
   Thus, Alice and Bob have a problem of how they can confidently “bootstrap” the exchange of public keys onto their communications session. More generally, the bootstrapping problem in a P2P setting involves exchanging any sort of public data or digital object such that the recipient is confident it came from the purported sender. 
   BRIEF SUMMARY OF THE INVENTION 
   Embodiments of the invention use the popular Simple Mail Transport Protocol (SMTP) for email exchange, to solve the bootstrapping problem of computer identities, for P2P communication. Typically this is a prerequisite for using algorithms like RSA that establish a logically secure communication channel over a physically insecure network. With the RSA algorithm the bootstrapping problem is one of how to have two peer computers exchange their mutual Public Keys without third party mediation (like Certificate Authorities). With other algorithms or technologies, the data involved in such a bootstrapping problem may be different, but the underlying problem of exchanging some public data with the confidence that there is no spoofing is the same. 
   Embodiments of the invention use existing electronic mail protocols, such as SMTP, to authenticate the exchange of public information. If the electronic mail protocols are strong, in that sending an email message to a given address results in the message reaching that address with a high degree of confidence, then the exchange of public information performed in accordance with embodiments of the invention is authenticated. 
   In one aspect of the invention, a method is provided for authenticating the sender of a digital object, comprising generating a first unique identifier (UID), transmitting to a previously known address, via an electronic mail protocol, a first message comprising the first UID, receiving, via the electronic mail protocol, a second message comprising a second UID and a copy of the first UID, and transmitting to the previously known address, via the electronic mail protocol, a third message comprising a copy of the second UID, wherein at least one of the messages transmitted to the previously known address further comprises the digital object. In one embodiment of the invention, the digital object is a public key for a cryptographic system. In embodiments of the invention, the electronic mail protocol comprises a mail server operating the Simple Mail Transport Protocol (SMTP). 
   In another aspect of the invention, a method is provided for authenticating the sender of a digital object, comprising receiving, via an electronic mail protocol, a first message comprising a first unique identifier (UID), generating a second UID, transmitting to a previously known address, via the electronic mail protocol, a second message comprising the second UID and a copy of the first UID, and receiving, via the electronic mail protocol, a third message comprising a copy of the second UID, wherein at least one of the messages received further comprises the digital object. In one embodiment, the digital object is a public key for a cryptographic system. In embodiments of the invention, the electronic mail protocol comprises a mail server operating the Simple Mail Transport Protocol (SMTP). 
   In another aspect of the invention, a computer-readable medium including computer-executable instructions is provided for facilitating authenticating a sender of a digital object, computer-executable instructions executing the steps of generating a first unique identifier (UID), transmitting to a previously known address, via an electronic mail protocol, a first message comprising the first UID, receiving, via the electronic mail protocol, a second message comprising a second UID and a copy of the first UID, and transmitting to the previously known address, via the electronic mail protocol, a third message comprising a copy of the second UID, wherein at least one of the messages transmitted to the previously known address further comprises the digital object. In embodiments of the invention, the digital object is a public key for a cryptographic system. In embodiments of the invention, the electronic mail protocol comprises a mail server operating the Simple Mail Transport Protocol (SMTP). 
   The present invention, viewed another way, comprises an apparatus is provided for authenticating the sender of a digital object, comprising a random number generator generating a first unique identifier (UID), a network interface transmitting to a previously known address, via an electronic mail protocol, a first message comprising the first UID, the network interface receiving, via the electronic mail protocol, a second message comprising a second UID and a copy of the first UID, and the network interface transmitting to the previously known address, via the electronic mail protocol, a third message comprising a copy of the second UID, wherein at least one of the messages transmitted to the previously known address further comprises the digital object. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the appended claims set forth the features of the present invention with particularity, the invention and its advantages are best understood from the following detailed description taken in conjunction with the accompanying drawings, of which: 
       FIG. 1  is a simplified schematic diagram illustrating an exemplary architecture of a computing device for carrying out an authentication protocol, in accordance with an embodiment of the invention; 
       FIG. 2  is an exemplary network communication arrangement for authenticating the sender of a digital object, in accordance with an embodiment of the invention; 
       FIG. 3  illustrates an exemplary component architectures for use in authentication, in accordance with an embodiment of the invention; 
       FIG. 4  illustrates a sample electronic mail message for use in sending and authenticating, in accordance with an embodiment of the invention; 
       FIG. 5  depicts a flow diagram showing a protocol for authenticating the sender of an digital object, in accordance with an embodiment of the invention; 
       FIG. 6  is a flow diagram illustrating a sender-employed method for use in authenticating a sender of a digital object, according to an embodiment of the invention; and 
       FIG. 7  is a flow diagram illustrating a receiver-employed method for use in authenticating a sender of a digital object, according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The methods and systems supporting secure key exchanges using email will now be described with respect to a number of embodiments; however, the methods and systems of the invention are not limited to the illustrated embodiments. Moreover, the skilled artisan will readily appreciate that the methods and systems described herein are merely exemplary and that variations can be made without departing from the spirit and scope of the invention. 
   The invention will be more completely understood through the following detailed description, which should be read in conjunction with the attached drawings. In this description, like numbers refer to similar elements within various embodiments of the present invention. The invention is illustrated as being implemented in a suitable computing environment. Although not required, the invention will be described in the general context of computer-executable instructions, such as procedures, being executed by a personal computer. Generally, procedures include program modules, routines, functions, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multi-processor systems, microprocessor based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. The term computer system may be used to refer to a system of computers such as may be found in a distributed computing environment. 
     FIG. 1  illustrates an example of a suitable computing system environment  100  on which the invention may be implemented. The computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment  100 . Although one embodiment of the invention does include each component illustrated in the exemplary operating environment  100 , another more typical embodiment of the invention excludes non-essential components, for example, input/output devices other than those required for network communications. 
   With reference to  FIG. 1 , an exemplary system for implementing the invention includes a general purpose computing device in the form of a computer  110 . Components of the computer  110  may include, but are not limited to, a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . The system bus  121  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus. 
   The computer  110  typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by the computer  110  and includes both volatile and nonvolatile media, and removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer  110 . Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of the any of the above should also be included within the scope of computer readable media. 
   The system memory  130  includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM)  131  and random access memory (RAM)  132 . A basic input/output system  133  (BIOS), containing the basic routines that help to transfer information between elements within computer  110 , such as during start-up, is typically stored in ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit  120 . By way of example, and not limitation,  FIG. 1  illustrates operating system  134 , application programs  135 , other program modules  136  and program data  137 . 
   The computer  110  may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only,  FIG. 1  illustrates a hard disk drive  141  that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk drive  151  that reads from or writes to a removable, nonvolatile magnetic disk  152 , and an optical disk drive  155  that reads from or writes to a removable, nonvolatile optical disk  156  such as a CD ROM or other optical media. Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, SmartCards, SecureDigital cards, SmartMedia cards, CompactFlash cards and the like. The hard disk drive  141  is typically connected to the system bus  121  through a non-removable memory interface such as interface  140 , and magnetic disk drive  151  and optical disk drive  155  are typically connected to the system bus  121  by a removable memory interface, such as interface  150 . 
   The drives and their associated computer storage media, discussed above and illustrated in  FIG. 1 , provide storage of computer readable instructions, data structures, program modules and other data for the computer  110 . In  FIG. 1 , for example, hard disk drive  141  is illustrated as storing operating system  144 , application programs  145 , other program modules  146  and program data  147 . Note that these components can either be the same as or different from operating system  134 , application programs  135 , other program modules  136 , and program data  137 . Operating system  144 , application programs  145 , other program modules  146 , and program data  147  are given different numbers hereto illustrate that, at a minimum, they are different copies. A user may enter commands and information into the computer  110  through input devices such as a tablet, or electronic digitizer,  164 , a microphone  163 , a keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  120  through a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor  191  or other type of display device is also connected to the system bus  121  via an interface, such as a video interface  190 . The monitor  191  may also be integrated with a touch-screen panel or the like. Note that the monitor and/or touch screen panel can be physically coupled to a housing in which the computing device  110  is incorporated, such as in a tablet-type personal computer. In addition, computers such as the computing device  110  may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  194  or the like. 
   The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 . The remote computer  180  may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  110 , although only a memory storage device  181  has been illustrated in  FIG. 1 . The logical connections depicted in  FIG. 1  include a local area network (LAN)  171  and a wide area network (WAN)  173 , but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. For example, in the present invention, the computer  110  may comprise the source machine from which data is being migrated, and the remote computer  180  may comprise the destination machine. Note however that source and destination machines need not be connected by a network or any other means, but instead, data may be migrated via any media capable of being written by the source platform and read by the destination platform or platforms. 
   When used in a LAN networking environment, the computer  110  is connected to the LAN  171  through a network interface or adapter  170 . Alternatively, the computer  110  contains a wireless LAN network interface operating on, for example, the 802.11b protocol, allowing the computer  110  to connect to the LAN  171  without a physical connection. When used in a WAN networking environment, the computer  110  typically includes a modem  172  or other means for establishing communications over the WAN  173 , such as the Internet. The modem  172 , which may be internal or external, may be connected to the system bus  121  via the user input interface  160  or other appropriate mechanism. Alternatively, the computer  110  contains a wireless WAN network interface operating over, for example, the General Packet Radio Service (GPRS), allowing the computer  110  to connect to the WAN  173  without a physical connection. In a networked environment, program modules depicted relative to the computer  110 , or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,  FIG. 1  illustrates remote application programs  185  as residing on memory device  181 . It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. Additionally, variations of the computer  110  may be incorporated into other exemplary systems for implementing the invention, such as cellular phones, personal digital assistants, and the like. 
   The invention is potentially incorporated into computing devices/machines used in a variety of networking environments. Turning to  FIG. 2 , a simple example of a networking environment is depicted wherein the invention can be exploited. A first computer  202 , used by a user “A” who wishes to transmit his public encryption key to user “B” via email, communicates with a mail server  204 . The computer  202  contains, for example, a mail application with which user “A” composes messages and transmits them to the mail server  204 . The mail server  204  uses a known and accepted mail protocol, such as the Simple Mail Transport Protocol (SMTP) to transmit electronic messages. A message created by user “A” typically contains an address for a recipient in the form of “userB@domain.com”. The characters to the right of the ‘@’ symbol, “domain.com” in this example, comprise the domain name, which is a logical domain for a computer receiving mail for user “B”. The mail server  204  obtains a corresponding physical address for the logical address by querying a Domain Name System (DNS) server  206 . The DNS server  206  belongs to a hierarchy of distributed DNS servers, which serves as mapping service between logical addresses and physical addresses. The physical address takes the form of an Internet Protocol (IP) address, which identifies a computer  208  on the Internet  210 . Embodiments of the invention establish a secure communications channel between the sending mail server  204  and the receiving mail server  212  by using Transport Layer Security (TLS), ensuring that communications between the two servers cannot be eavesdropped. The mail server  204  sends the email message with the obtained physical address using the TCP/IP protocol, causing it to be routed over the Internet  210 . The message reaches a computer  208  associated with the IP address that acts as a mail server for user “B”. User “B”, the intended recipient of the message, uses a computer  212  to obtain email messages intended for him. Computer  212  communicates with mail server  208  and receives the appropriate messages. Similarly, when user “B” attempts to send an email message over the Internet  210 , the mail server  208  queries a DNS server  214  to obtain the physical address of the intended recipient. 
     FIG. 3  illustrates a set of software components executing on the user computer  202  in accordance with an embodiment of the invention. The user interacts with a mail application program  302  to send and receive email messages. An exemplary mail application program is Outlook, by the MICROSOFT CORPORATION of Redmond, Wash. The mail application  302  sends and receives both text and binary files, such as executable programs, documents or other files. A single message sent or received by the mail application  302  can contain text, binary files, or both. Embodiments of the invention facilitate the exchange of public cryptographic keys, such as those used in the RSA cryptographic scheme. In such a scheme, a user mathematically creates two keys: a private key  304  and a public key  306 . The user makes the public key  306  available to anyone, while he keeps the private key  304  a secret. Although anyone can encrypt a message using the public key  306 , only a holder of the private key  304  is able to decrypt the encrypted message. The mathematical properties of the scheme also allow the user to digitally ‘sign’ messages by encrypting them with his private key  304 . Anyone holding the public key  306  can decrypt the message to verify it was written by the user. The exemplary RSA scheme is more fully described in U.S. Pat. No. 4,405,829, which is hereby incorporated in its entirety by reference. The user computer  202 , in an embodiment of the invention, contains an encryption/decryption engine  308  for manipulating encrypting and decrypting operations involving the private key  304  and public key  306 . 
   Embodiments of the invention also contain a random number generator  310 . The random number generator  310  preferably produces a string of bits such that it is practically infeasible to predict any bit of the sequence given any other bits of the sequence. Thus, it is not necessary that the sequence is truly random, but the sequence must appear random to a sufficient degree of unpredictability. Embodiments call functions such as the UuidCreate function provided by the Microsoft Developer Network, which use pseudo-random number generators employing algorithms to generate a globally unique identifier. 
     FIG. 4  shows a typical email message  400  with headers, as used in an embodiment of the invention. In embodiments of the invention, the format of an email message complies with RFC 822. In the example message  400 , a sender claiming to have the address “john@uchicagox.edu” is sending a message containing a Microsoft Excel file  401  to a recipient at the address “arf@arfdomainx.com”. Other attachments, such as public-keys for cryptographic protocols, are alternatively attached. Several headers  402  at the top of the message contain routing information tracing the route of the message  400  from the sender to the recipient. The sender has indicated in a “From” header  404  that his name is “John Smith” and his address is “john@uchicagox.edu”. The sender also affirms this is his address in the signature field  405  in the body of the message. However, other headers, such as the “Received” header  406  and the “Return-Path” header  408  indicate the message is actually sent from a different address, “john@realaddress.org”. In fact, the headers indicating the sender&#39;s address can be faked, or “spoofed” with varying degrees of difficulty. With some messages, a savvy sender can spoof the return addresses to make it impossible to determine with certainty the sender&#39;s actual address. In other words, the recipient of a message does not always have confidence that the message actually came from the purported sender. 
   The message  400  also contains a “To” header  410 . The “To” header  410  indicates where the message should be sent, in this case to “arf@arfdomainx.com”. Unlike the “From” headers  404 ,  405 ,  406  and  408 , the “To” header is difficult to spoof. That is, if a sender sends a message to a recipient addressed in the “To” field, there is a high degree of confidence that the message will reach the recipient, and not be redirected somewhere else instead. 
   Turning to  FIG. 5 , a method is described whereby two users, A and B, of networked computers exchange public keys such that each trusts the authenticity of the other, in accordance with an embodiment of the invention. The method assumes that each user of the two computers has prior knowledge of the other user&#39;s email address. The first computer, used by user A, generates a unique identifier, UID 1 , at step  502  using a random or pseudo-random number generator. The unique identifier is sufficiently large that it is difficult to guess. In practice, 128 bits suffice to ensure the identifier is unique. The first computer stores UID 1 , indexed by the email address for user B, at step  504 . The first computer sends UID 1 , along with user A&#39;s public key, to the second computer by using the previously known email address of user B, at step  505 . 
   The second computer receives the message and stores a copy of UID 1 , user A&#39;s public key, and the email address listed in the “From” field of the message, at step  506 . The second computer then uses, by way of example, a random or pseudo-random number generator to create a unique identifier, UID 2 , at step  508 . UID 2  is preferably at least 128 bits in length. The second computer sends user B&#39;s public key, along with UID 2  and a copy of UID  1 , to the first computer, at step  510 . This message, however, is addressed using the previously known address for user A, disregarding any return email address in a “From” or “Reply To” field of the first message. 
   At step  512 , the first computer receives the message from the second computer and verifies that the copy of UID 1  is accurate, using the email address in the “From” field to index the locally stored UID 1 . User A then trusts that the public key received from user B is authentic (i.e., that it actually came from user B) at step  514 . The first computer then sends a copy of UID 2  back to user B, at step  516 . 
   The second computer receives the message and verifies that the copy of UID 2  is accurate, using the email address in the “From” field to index the locally stored UID 2 , at step  518 . User B then trusts that the public key received from user A is authentic (i.e., that it actually came from user A), at step  520 . 
     FIG. 6  illustrates a method for using email to send a user&#39;s public key such that the recipient has confidence that the public key came from the user, in accordance with an embodiment of the invention. The user first generates a unique identifier (UID 1 ) at step  602  using, by way of example, a random or pseudo-random number generator. The unique identifier is sufficiently large that it is difficult to guess. In practice, 128 bits suffice to ensure the identifier is unique. At step  604 , the user sends an email message containing his public key and UID 1  to a previously known address for the recipient. The user monitors for a timely response that contains a second unique identifier, UID 2 , at step  606 . In some embodiments, a timespan for monitoring at step  606  is configurable by the user. If a timely response is not received, the user begins again at step  602 . Otherwise, the user checks that the response contains a copy of UID 1  at step  608 . If the copy of UID 1  is incorrect, the user begins again at step  602 . Otherwise, the user sends an email containing a copy of UID 2  to the recipient at step  610 . 
     FIG. 7  illustrates a method for using email to receive a sender&#39;s public key such that the user has confidence that the public key came from the sender, in accordance with an embodiment of the invention. The user receives an email at step  702  containing a public key and a unique identifier, UID 1 . Although the message contains a “From” field identifying a sender, the user is not confident that the message actually came from the purported sender. The user generates a unique identifier UID 2  at step  704  using a random or pseudo-random number generator. He sends an email message containing UID 2  and a copy of UID 1  to the purported sender, but by using a previously known address for the sender, at step  706 . The user monitors for a timely response at step  708 . In some embodiments, the amount of time used for monitoring at step  708  is configurable by the user. If a timely response is not received, the user ends the protocol at step  710 . Alternatively, if a timely response is not received, the user resends the message containing UID 2  and a copy of UID 1  at step  706 . Otherwise, the user checks that the response contains a copy of UID 2  at step  712 . If the copy of UID 2  is incorrect, the protocol ends at step  710 . Otherwise, the user is convinced that the public key came from the purported sender, and begins to trust the key at step  714 . 
   Embodiments of the invention further allow the exchange of digital objects other than public keys. For example, a first user can use an embodiment of the invention to send a document to a second user so that the second user is convinced that it was, indeed, the first user who sent the document. More generally, embodiments of the invention enable authentication of parties simultaneously with the transmission of digital objects by “bootstrapping” the objects to email messages. In the instance when the digital object is a public key, the authenticated key can be subsequently used for secure communications between the parties. 
   In view of the many possible embodiments to which the principles of the present invention may be applied, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of the invention. For example, those of skill in the art will recognize that the illustrated embodiments can be modified in arrangement and detail without departing from the spirit of the invention. Although the invention is described in terms of software modules or components, those skilled in the art will recognize that such may be equivalently replaced by hardware components. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.