Abstract:
System and method for determining the updating time by a server presumed to have a correct time and a client needing a correct time. The server can first transmit an unencrypted signal, which may be signed or unsigned. The server can then later encrypt or sign the same packet it transmitted with a private key and transmit it to the client. After the client receives the unencrypted packet, the client can compute a time difference. However the client doesn&#39;t update its time until a follow-up packet is received from the server. If encrypted, the packet is decoded with the server&#39;s public key, and the decoded packet is shown identical to the received packet and that the identification bits are the same.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       BACKGROUND 
       [0002]    Methods and systems disclosed herein relate generally to synchronizing data across a network and more generally to authenticating a Network Time Protocol (NTP). NTP is a User Datagram Protocol-based protocol used to synchronize time clocks among network devices. NTP is standards-based and defined in RFC 5905, Network Time Protocol Version 4, June 2010, http://tools.ietf.org/html/rfc5905 (RFC 5905). According to RFC 5905, “The [NTP] implementation model . . . is based on a threaded, multi-process architecture, although other architectures could be used as well. The on-wire protocol . . . is based on a returnable-time design that depends only on measured clock offsets, but does not require reliable message delivery. Reliable message delivery such as TCP can actually make the delivered NTP packet less reliable since retries would increase the delay value and other errors. The synchronization subnet is a self-organizing, hierarchical, master-slave network with synchronization paths determined by a shortest-path spanning tree and defined metric. While multiple masters (primary servers) may exist, there is no requirement for an election protocol.” (RFC 5905, p. 4) Since NTP is used to ensure accurate timestamp information, NTP can pose a security risk. If malicious users were able to falsify NTP information passed over the network, timestamp information could be falsified to the advantage of the malicious user. In order to deal with this vulnerability, NTP optionally implements an authentication mechanism. Authentication can be a digital signature that doesn&#39;t include data encryption. A data packet including the time plus a key can be used to build a non-reversible magic number that can be appended to the packet. The client that has the same key does the same computation done by the server to create the data packet, and then compares the result. If the results match, authentication succeeded. This type of authentication can protect the client from hackers and spoofers who set up servers that claim to be a recognized authority, such as the U.S. Naval Observatory or the National Institute of Standards and Technology, but instead are giving out a false representation of the time. The simplest method to provide authentication would be for the server to fully encrypt the packet responses with a private key. The client could then apply the server&#39;s public key to decrypt the packet; this could be achieved by many means including those currently used for financial transactions on the internet. Unfortunately it has been shown that such systems are not applicable to NTP because the time and CPU resources involved in encrypting and decrypting are large enough to distort the response and to increase the time transfer errors to an unacceptable level. Therefore encryption has been abandoned in favor of the simple authentication previously described. 
         [0003]    What is needed is a system in which complex schemes for key transmission need not be applied in real-time, or even applied at all. What is further needed is a system similar to those currently used by the financial sector in which there is no need to sign or authenticate the initial packet sent by the server. 
       SUMMARY 
       [0004]    The system and method of the present embodiment can determine the time difference between two computers, which are designated a server computer and a client computer. The server computer is presumed to have the correct time, and the client computer is presumed to need the correct time. In the present embodiment, the client computer can begin by sending an NTP packet request to the server computer. In an alternate embodiment, the server computer can broadcast a server time without being prompted by the client computer. The NTP packet can include the time of transmission and could also include self-generated identification-bits chosen to be relatively unpredictable to outsiders. The server computer can respond with a server packet that can embed any received identification bits and optional server-added identification bits along with the information normally part of an NTP packet, including the received time of client transmission, the time of reception at the server, and the time of retransmission by the server. To sidestep the delay issue, the server can first transmit an unencrypted signal, which may be signed or unsigned. The server can then later encrypt or sign the same packet it transmitted with a private key and transmit it to the client. After the client receives the unencrypted packet, the client can compute a time difference. However, the client doesn&#39;t update its time until a follow-up packet is received from the server. If encrypted, the packet is decoded with the server&#39;s public key, and the decoded packet is shown identical to the received packet and that the identification bits are the same. If the server&#39;s follow-up packet is signed, the client verifies the initial packet against the signed packet. 
         [0005]    Alternatively, the encrypted version can be sent from a second server associated with the first server, for example, an identical outgoing packet can be sent from the second server that is directly connected to the first server, or alternatively connected by a switch or router along the outgoing path. The second server can either be sent a copy of the original packet, or can read and retransmit it. The second server can send the encrypted packet to the client. This separation of functions among multiple servers could improve the time transfer accuracy. 
         [0006]    The method of the present embodiment for minimizing delay in updating a client time at a client computer can include, but is not limited to including, receiving, by the client computer, set-up information including options from a server computer. The method can also include receiving, by the client computer, default values from a server computer. The method can further include transmitting, by the client computer to the server computer, a client packet including client identification information, timing information, and selected ones of the options. If in broadcast mode, the client&#39;s step of transmitting can be omitted. The method can still further include receiving, by the client computer, a server packet including at least one server time and at least one retransmission time that are formatted according to the selected options, and computing, by the client computer, a time difference between the at least one server time and the client time. The method can also include receiving, by the client computer, a secure version of the server packet. The secure version can include at least one secure time. The method can also include updating, by the client computer, the time based on the time difference only if the at least one secure time and the at least one server time match. 
         [0007]    The options can optionally include a time format, a security option, and commercially-available packages. The security option can include an encryption method and a decryption key. The method can optionally include decrypting the secure version according to the decryption key. The decrypted secure version can include decrypted client information. The method can further optionally include updating, by the client computer, the time based on the time difference only if the decrypted time and the received time match, and if the received client identification information and the decrypted client identification information match. The server packet can optionally be signed, and the method can further optionally include verifying the server packet against the signed server packet. The method can further optionally include receiving, by the client computer, the secure version of the server packet from a first server computer and the secure packet from a second server computer. The first server computer and the second server computer are related by means such as, for example, but not limited to, direction connection or switch/router feed. The method can still further optionally include updating, by the client computer, the client time based on the time difference only if the client time and the server time match, and all other information in the secure version and the server packet match. The method can further optionally include indicating, by the client computer, a possible spoof when the secure version and the server packet do not match. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a NTP packet format according to NTP version  4 ; 
           [0009]      FIG. 2  is a schematic block diagram of a protocol between server computer and client computer of an embodiment of the present teachings; 
           [0010]      FIG. 3  is a schematic block diagram of a configuration for an alternate embodiment of the present teachings; 
           [0011]      FIG. 4  is a schematic block diagram of a protocol between server computer and client computer of another embodiment of the present teachings; 
           [0012]      FIG. 5  is a flowchart of one embodiment of the method of the present teachings; 
           [0013]      FIG. 6  is a flowchart of an alternate embodiment of the method of the present teachings; 
           [0014]      FIG. 7  is a schematic block diagram of one embodiment of the system of the present teachings; and 
           [0015]      FIG. 8  is a schematic block diagram of another embodiment of the system of the present teachings. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The problems set forth above as well as further and other problems are solved by the present teachings. These solutions and other advantages are achieved by the various embodiments of the teachings described herein below. The system and method of the present embodiment automatically minimize delay in updating time at a client computer. 
         [0017]    Referring now to  FIG. 1 , NTP version  4  packet  10  is a User Datagram Protocol (UDP) datagram including a basic header—leap indicator  11 , version number  13 , mode  15 , stratum  17 , poll exponent  21 , precision exponent  25 , root delay  27 , root dispersion  29 , reference identification  31 , reference timestamp  33 , origin timestamp  35 , receive timestamp  37 , and transmit timestamp  39 . NTP packet  10  also includes optional extension fields  41  and  43  including, for example, but not limited to, a destination timestamp. Finally, NTP packet includes an optional message authentication code including key identification  45  and message digest field  49 . Leap indicator  11  warns of an impending leap second, version number  13  is the NTP version number, and mode  15  indicates, among other things, whether or not NTP packet  10  is part of a time broadcast. Stratum  17  indicates the reliability of the time source, poll  21  is the maximum interval between successive messages, and precision is the precision of the system clock of the computer creating NTP packet  10 . Root delay  27  is the total round-trip delay to the reference clock, root dispersion  29  is the total dispersion to the reference clock, reference identification  31  identifies a particular server computer or reference clock, and reference timestamp  33  is the time when the system clock of the system identified by reference identification  31  was last set or corrected. Origin timestamp  35  is the time at the client computer when the request departed for the server computer, receive timestamp  37  is the time at the server computer when the request arrived from the client computer, and transmit timestamp  39  is the time at the server computer when the response left for the client computer. Destination timestamp, possibly located in optional extension field  41 , is the time at the client computer when the reply arrived from the server computer. Destination timestamp is determined upon arrival of NTP packet  10 . Key identifier  45  is used by the client and server computers to designate a secret 128-bit MD5 algorithm key defined in RFC 1321 and used to verify data integrity. Message digest  49  is calculated over the NTP header and optional extension fields, but not including key identifier  45  and message digest  49 . 
         [0018]    Referring now to  FIG. 2 , protocol  20  can include, but is not limited to including, server computer  19  sending set-up options  135  to client computer  102 , which executes set-up processor  101  receiving and processing set-up options  135  including, for example, but not limited to, a security option and a time format. Packet processor  103  sends client packet  123  that is a time request, and that can include, but is not limited to including, NTP packet  10  ( FIG. 1 ) including origin timestamp  35  ( FIG. 1 ), and client identification information. Server packet creator  51  creates and sends server packet (or packets)  128  that can include, but is not limited to including, client identification information, server identification information, NTP packet  10  ( FIG. 1 ) including receive timestamp  37  ( FIG. 1 ) and transmit timestamp  39  ( FIG. 1 ). Time processor  107  computes, by client computer  102 , a time difference between client time  131  ( FIG. 7 ) and at least one of the server times (receive timestamp  37  ( FIG. 1 ) and transmit timestamp  39  ( FIG. 1 )). The measured time difference is calculated as 0.5*(SR+ST−CR−CT), where SR is receive timestamp  37  ( FIG. 1 ), ST is transmit timestamp  39  ( FIG. 1 ), CR is the destination timestamp, and CT is origin timestamp  35  ( FIG. 1 ). Secure packet processor  109  receives secure packet  111  which is an encrypted and optionally signed version of server packet  128 . Secure packet processor  109  decodes secure packet  111  with a public key and compares server packet  128  with the unencrypted version of secure packet  111 . Identification bits can be compared as well. If secure packet  111  and server packet  128  are signed, secure packet processor verifies the signatures. Should the packets pass verification test, update processor  105  can compute an updated time  119  ( FIG. 7 ) by updating the client time  131  ( FIG. 7 ) based on the measured time difference and via the client&#39;s time computation system&#39;s parameters. If the packets do not pass verification tests, spoof processor  23  can test for spoofing and can set spoof indication  127  ( FIG. 7 ) if a spoof has been attempted. 
         [0019]    Referring now to  FIG. 3 , in an alternative embodiment, in configuration  30 , server  1  computer  19 A sends server packet  128  ( FIG. 2 ) to client computer  102 . Processing as above occurs in client computer  102 . However, the subsequent transmission of secure packet  111  is generated by server  2  computer  19 B and sent to client computer  102 . Server  1  computer  19 A can have a relationship with server  2  computer  19 B such as, for example, but not limited to, being directly wired to server  2  computer  19 B as indicated in  FIG. 3  by dashed lines, or can involve some form of electronic communications  124  such as a router. 
         [0020]    Referring now to  FIG. 4 , protocol  40 , which operates in the context of configuration  30  ( FIG. 3 ), can include, but is not limited to including, more than one server—server  1  computer  19 A and server  2  computer  19 B in the depicted embodiment—and client computer  102 . In protocol  40 , server  1  computer  19 A sends set-up options  135  to client computer  102  which processes are similar to client computer  102  processes in protocol  20  ( FIG. 2 ). However, server  1  computer  19 A executes server unencrypted packet creator  51 A to send server packet  128  to client  102 , which server  2  computer  19 B executes server encrypted packet creator  51 B to send secure packet  111  to client  102 . Server  1  computer  19 A can also share server packet  128  with server  2  computer  19 B, forming a relationship between server  1  computer  19 A and server  2  computer  19 B. 
         [0021]    Referring now to  FIG. 5 , method  150  of the present embodiment can include, but is not limited to including, receiving  151 , by the client computer, set-up information including options and possibly defaults from at least one server computer. The options could, for example, but not limited to, be indirectly available via such means as public web pages or internal computation. Method  150  can also include transmitting  153 , by the client computer to at least one server computer, a client packet including client identification information, timing information, and selected options from the options. If  152  the server computer is operating in broadcast mode, no transmitting step is required from the client. Method  150  can also include receiving  155 , by the client computer, a server packet including at least one server time formatted based on the selected options and possibly the default options, computing  157 , by the client computer, a time difference between the at least one server time and the client time, receiving  159 , by the client computer, a secure version of the server packet, the secure version including secure time data, and updating  161 , by the client computer, the client time based on the time difference only if the secure time data and the server data associated with at least one server time match. 
         [0022]    Referring now to  FIG. 6 , method  250  for circumventing spoofing of time-critical data can include, but is not limited to including, receiving  251 , by the client computer, set-up information including options from at least one server computer. The options could, for one example, be indirectly available via such means as public web pages or internal computation. Method  250  can also include transmitting  253 , by the client computer to at least one server computer, a client packet including client identification information, timing information, and selected options from the options. If  252  the server computer is operating in broadcast mode, no transmitting step by the client is required. Method  250  can also include receiving  255 , by the client computer, a server packet including server data formatted based on the options or the selected options, computing  257 , by the client computer, at least one difference between the server data and the time-critical data, receiving  259 , by the client computer, a secure version of the server packet, the secure version including secure time-critical data, and updating  261 , by the client computer, the time-critical data based on the at least one difference only if the secure data and the server data match. The options can include an encryption method and a decryption key. Method  250  can optionally include decrypting the secure version according to the decryption key, the decrypted secure version including decrypted client information, updating, by the client computer, the data based on the at least one difference only if the decrypted data and the server data match, and if the received client identification information and the decrypted client identification information match, and indicating, by the client computer, a possible spoof when the secure version and the server packet do not match. 
         [0023]    Referring now to  FIG. 7 , system  100  for minimizing delay in updating client time  131  at client computer  102  can include, but is not limited to including, set-up processor  101  receiving, by client computer  102 , set-up information including options  135  from at least one server computer  19 . The options could also be indirectly available by, for example, but not limited to, such means as public web pages or internal update mechanisms. System  100  can also include packet processor  103  optionally transmitting, by client computer  102  to at least one server computer  19 , client packet  123  including client identification information, timing information, and selected options from options  135 . Packet processor  103  can also receive, by client computer  102 , server packet  128  including sever time data and at least one server time  47  formatted based on the options or the selected options. System  100  can also include time processor  107  computing, by client computer  102 , a time difference between at least one server time  47  and client time  131 , and secure packet processor  109  receiving, by client computer  102 , a secure version  111  of server packet  128 , secure version  111  including secure time data. System  100  can also include update processor  105  updating, by client computer  102 , time  131 , creating updated time  119 , based on the time difference only if the secure time data and the server time data associated with the at least one server time  47  match. Security options  133  can include an encryption method and a decryption key. Secure packet processor  109  can also decrypt the secure version according to the decryption key. The decrypted secure version can include decrypted client information. Update processor  105  can update, by client computer  102 , time  131  based on the time difference only if the decrypted time and at least one server time  47  match, and if the received client identification information and the decrypted client identification information match indicated by, for example, but not limited to, update switch  132 . System  100  can optionally include spoof processor  23  indicating, by client computer  102 , a possible spoof using, for example, but not limited to, spoof indication  127 , when the secure version  111  and server packet  128  do not match indicated by, for example, but not limited to, update switch  132 . Options can include an encryption method, a decryption key, and time format  134 . Secure packet processor  109  can optionally decrypt secure version  111  according to the decryption key. The decrypted secure version can include decrypted client identification information. Update processor  105  can optionally update, by client computer  102 , client time  131  based on the time difference only if the decrypted time and at least one server time  47  match, and if the received client identification information and the decrypted client identification information match. 
         [0024]    Referring now to  FIG. 8 , system  200  for circumventing spoofing of time-critical data  138  at client computer  102  can include, but is not limited to including, set-up processor  101  receiving, by client computer  102 , set-up information including options  135  from at least one server computer  19 . The options could also be indirectly available by, for example, but not limited to, such means as public web pages or internal update mechanisms. System  200  can also include packet processor  103  optionally transmitting, by client computer  102  to at least one server computer  19 , client packet  123  including client identification information, timing information, and selected options from options  135 . Packet processor  103  can also receive, by client computer  102 , server packet  128  including sever time data and server data  48  formatted based on the options or the selected options. System  200  can also include server data processor  142  computing, by client computer  102 , at least one difference between server data  48  and time-critical data  138 , and secure packet processor  109  receiving, by client computer  102 , a secure version  111  of server packet  128 , secure version  111  including secure time-critical data. System  200  can also include update processor  105  updating, by client computer  102 , time-critical data  138 , creating updated data  120 , based on the at least one difference only if the secure data and server data  48  match. Security options  133  can include an encryption method and a decryption key. Secure packet processor  109  can also decrypt the secure version according to the decryption key. The decrypted secure version can include decrypted client information. Update processor  105  can update, by client computer  102 , time-critical data  138  based on the at least one difference only if the decrypted time and server data  48  match, and if the received client identification information and the decrypted client identification information match indicated by, for example, but not limited to, update switch  132 . System  200  can optionally include spoof processor  23  indicating, by client computer  102 , a possible spoof using, for example, but not limited to, spoof indication  127 , when the secure version  111  and server packet  128  do not match indicated by, for example, but not limited to, update switch  132 . Options can include an encryption method, a decryption key, and data format  136 . Secure packet processor  109  can optionally decrypt secure version  111  according to the decryption key. The decrypted secure version can include decrypted client identification information. Update processor  105  can optionally update, by client computer  102 , time-critical data  138  based on the at least one difference only if the decrypted data and server data  48  match, and if the received client identification information and the decrypted client identification information match. 
         [0025]    Embodiments of the present teachings are directed to computer systems such as system  100  ( FIG. 7 ) and system  200  ( FIG. 8 ) for accomplishing the methods such as method  150  ( FIG. 5 ) and method  250  ( FIG. 6 ) discussed in the description herein, and to computer readable media containing programs for accomplishing these methods. The raw data and results can be stored for future retrieval and processing, printed, displayed, transferred to another computer, and/or transferred elsewhere. Communications links such as electronic communications  124  ( FIG. 7 ) can be wired or wireless, for example, using cellular communication systems, military communications systems, and satellite communications systems. In an exemplary embodiment, the software for the system is written in FORTRAN and C. The system can operate on a computer having a variable number of CPUs. Other alternative computer platforms can be used. The operating system can be, for example, but is not limited to, LINUX®. 
         [0026]    The present teachings are also directed to software for accomplishing the methods discussed herein, and computer readable media storing software for accomplishing these methods. The various modules described herein can be accomplished on the same CPU, or can be accomplished on different computers. In compliance with the statute, the present embodiment has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the present embodiment is not limited to the specific features shown and described, since the means herein disclosed comprise forms of putting the present teachings into effect. 
         [0027]    Methods such as method  150  ( FIG. 5 ) and method  250  ( FIG. 6 ) of the present teachings can be, in whole or in part, implemented electronically. Signals representing actions taken by elements of the system and other disclosed embodiments can travel over at least one live communications network  124  ( FIG. 7 ). Control and data information can be electronically executed and stored on at least one computer-readable medium. System  100  ( FIG. 7 ) and system  200  ( FIG. 8 ) can be implemented to execute on at least one computer node in at least one live communications network  124  ( FIG. 7 ). Common forms of at least one computer-readable medium can include, for example, but not be limited to, a floppy disk, a flexible disk, a hard disk, magnetic tape, or any other magnetic medium, a compact disk read only memory or any other optical medium, punched cards, paper tape, or any other physical medium with patterns of holes, a random access memory, a programmable read only memory, and erasable programmable read only memory (EPROM), a Flash EPROM, or any other memory chip or cartridge, or any other medium from which a computer can read. Further, the at least one computer readable medium can contain graphs in any form including, but not limited to, Graphic Interchange Format (GIF), Joint Photographic Experts Group (JPEG), Portable Network Graphics (PNG), Scalable Vector Graphics (SVG), and Tagged Image File Format (TIFF). 
         [0028]    Although the present teachings have been described with respect to various embodiments, it should be realized these teachings are also capable of a wide variety of further and other embodiments.