KR20010040248A - Method and system for transient key digital time stamps - Google Patents

Abstract

An undeniable public key digital sign time stamp 1040 is generated and used, for example, based on the concept of a secret cryptographic key 2010 associated with a transient time interval, which digitally signs data submitted during a particular time interval. Used and then destroyed (2040). The public key correlation for each time interval is stored for later authentication of the content of the time stamped data and the creation time of the time stamped data. The validity of the public key is ensured by authenticating the public key of each time interval using the private key of the previous time interval just before the private key is destroyed.

Description

Transient Key Digital Time Stamp Method and System {METHOD AND SYSTEM FOR TRANSIENT KEY DIGITAL TIME STAMPS}

The concept of a chain of evidence has long been the fundamentalism of the US trial system. Many legal situations rely on the ability to testify that some of the evidence exists at any point in time and is not constantly changing. In the past, where most possible forms of evidence consisted of data objects, there was a need for a protocol of chain of witnesses to verify the accuracy of the evidence in question. Historically, if evidence is only under the control of a limited number of individuals, and if all individuals verify the location and condition of the object, the court will accept claims of certainty of evidence.

Of course, such a system depends on the availability of reliable witnesses that are available and that can be verified under any given situation. Occasionally, witnesses may be available but not reliable. This is especially the case for document attestation, where the details of when a particular document is softened or signed are contained in the question. Obviously, the system needed to make it easy to obtain "witness on demand" in many situations.

This proof-of-concept concept is critical to much of the effort, resulting in a formalized system of professional document witnesses, for example, the Notary public service. Notary Public Notary focuses on such things as the existence of the document and the identification of the document holder or signer for the remuneration. Of course, a notary public cannot take any oath of knowledge of the actual content of the document, because the notary public requires permanent preservation (an impractical requirement) of all the certified documents. Most trusts are kept in a notary public notary system in connection with a generally supported litigation case, which is to forge stamps and signatures of notary public notaries or to buy testimony of a notary public. However, as computer graphics and desktop publishing techniques improve, the level of difficulty of forged documents and signs will be significantly reduced. The result of this improvement is that some states, such as California, no longer accept notarization as an absolute proof of document validity.

Most of this information is stored, accessed, and managed through computer database management systems. All major database systems allow time stamping of data at the time of writing. Many commercial and government systems rely on the assumption of the accuracy of these database time stamps. It is assumed that time stamps can be trusted in their database if the organization is trustworthy. Indeed, this claim requires, in literary terms, a "willing suspension of disbelief." Of course, no one can assume that every individual in a large organization can be trusted even if the organization itself is trustworthy. Moreover, it is well known that no conventional computer database system can be exempt from the possibility of data tampering or "hacking" by dishonest individuals.

One method developed to address some of these problems is based on a technique called "public key" cryptography. One of the most well known of these types of systems is a program called Pretty Good Privacy, which uses the Rivest-Shamir-Adleman (RSA) public key cryptographic system, distributed by the Massachusetts Institute of Technology. These systems are built around the concept of encrypting data in a way that allows both secure transmission and authentication of sensed data. The public key system uses an encryption key pair for each encryption / decryption event. One key is kept secret by the owner (e.g. secret key) and the other key is distributed (e.g. public key). A message encrypted with one of the keys in the key pair can only be decrypted with the other key, and vice versa.

The system allows encryption of data for one individual, for example using a first private public key. The message is sent to the second person through an unsecured channel, where only the second person has access to the unencrypted data because it can only be decrypted with the private key of the second person.

Before using the private key of the second individual to encrypt the data, the first individual uses his private key to encrypt the data, thereby digitally signing the data. The recipient uses the sender's public key to decrypt it, thereby providing that it only comes from the recipient because the recipient only uses the secret key to sign the data. Such a system provides both a mechanism for authentication and identification of the sender and the confidentiality of the data. It also demonstrates that the data cannot be altered in any way because it is encrypted by the sender. The public keys themselves can be " authenticated " by signing them (eg, digital signing) with the private key of a trusted individual. Others can access the issued public key's certificate by authenticating them using the private key of a trusted individual. If a trusted person subsequently loses trust in the validity of the authenticated key, that person is signed by the private key of the trusted person, informing others that the previously authenticated public key can no longer be trusted in the future. You can issue a revocation certificate.

The public key algorithm is very slow. Because of this, virtually all public key digital signing systems use what are called "cryptographically strong one-way hash functions" to produce what are called "message summaries" from the data to be signed. This message summary is the only representation of the data, a kind of data fingerprint, much smaller than the raw data. For example, a message digest using PGP is only 128 bits long. The message digest is encrypted using the sender's private key before sending the data to the recipient. The recipient can use the sender's public key to automatically decrypt the message digest and verify that it actually matches the raw data. This is a very secure system because it is computationally impractical for an attacker to devise alternative messages that provide the same message digest. Most of the estimates explain that it takes more than 10 ^ 12 years to continuously assemble a 128-bit message digest using the algorithm used by the PGP software package. In addition, further altering a single-byte summarized message prevents the hash function from matching the message summary to unencrypted data.

Therefore, the public key digital signature can prove irrefutable that the signed data is first signed with a given private key and the data does not change in any way because the signing has been performed. Systems such as PGP regularly attach a time stamp to their digital key and their digital signature each time they are created. However, this time stamp depends only on the internal clock in the computer to be used, and thus is inaccurate or deceived by intentionally changing the time individually on the computer clock to falsely indicate that a certain digital sign was created at a particular point in time.

Because of this, a new type of notarization is emerging that uses a public key digital signature to notarize digital information submitted over the Internet. So-called "digital notary" is a business that agrees to provide such services and stop the accuracy of the contents of the raw data as well as the time of signing. This is a significant improvement over the notarized notary concept because the new digital notary services can demonstrate that digitally signed data by their services exists at a certain point in time and does not change in any way because of that point in time. Because there is. The biggest problem with such digital notarization services, and the motivation for the method according to the present invention, is the fact that the authentication of digital-notarized-generated digital signs depends entirely on the reliability of the individuals and laboratories that run them. to be.

To solve this problem, the system needs to automatically and accurately verify the accuracy of digital time stamps without relying on the reliability of the individual or laboratory operating the digital notarization service. Transient key digital time stamps according to embodiments of the present invention provide these possibilities.

The present invention relates to a method of digital time stamping data. In particular, the present invention relates to digital time stamping of data by chaining of key pairs without the need for the next third party verification, where the key pairs are generated at specific time intervals.

1 is an exemplary flowchart for a digital time stamping method according to an embodiment of the present invention.

2A is a flowchart of another digital time stamping method according to an embodiment of the present invention.

2B is a flow chart of another digital time stamping method according to an embodiment of the present invention.

Figure 3A shows a first embodiment of a time stamping system according to the present invention.

Figure 3B shows a second embodiment of a time stamping system according to the present invention.

According to one embodiment of the invention, an irrefutable public key digital sign time stamp is generated and used. The system is based, for example, on the concept of a secret encryption key associated with a transient time interval that is used to digitally sign data submitted during a particular time interval and is permanently lost. The public key is correlated every time the interval is stored for future authentication of the time stamped data creation time and the contents of the time stamped data. Validation of the public key is ensured through authentication (eg signing) of the public key at each time interval, using the secret key at the previous time interval just before the secret key is lost.

The time stamping method according to an embodiment of the present invention provides a mechanism for proving irrefutable that a set of data exists at a predetermined time interval and does not change due to the time interval. A significant advantage of the present invention is that it provides non-repudiation to the user. It is difficult to deny the accuracy of the time stamp certificate generated by the method according to one embodiment of the invention. For example, the system is not based on any external "authentication authority" or the reliability of any external time tracking system. Rather, everything needed to authenticate a time stamp generated in accordance with one embodiment of the invention is for example time stamped data, sign from time stamp certificate, public key of time interval from time stamp certificate, and freedom of PGP. It is also the standard public key certification program as the commercial version. Other public key cryptography programs, such as the J / Cryptographic Specialization Cryptography Classification (http://www.baltimore.ie/products/jcrypto/index.html) for Java developers, may also be used in the present invention. Moreover, the method according to an embodiment of the present invention can operate on any kind of computer data. The system using the transient key digital time stamping method according to the present invention can be set up as an internet server stamping all requests for a free-for-service basis. The generation time and interval status of the information can be proved without risking the confidentiality of the sensed data. The time stamping method according to one embodiment of the present invention is a suitable method for use in the invention document system. Thus, the method according to one embodiment of the present invention can be used to authenticate critical secret records, such as medical records and money transactions, can be easily applied to any computer platform and does not depend on any particular public key algorithm.

1 illustrates an exemplary flowchart for a digital time stamping method according to an embodiment of the present invention. In step 1010 the key pair is generated at time interval t _n . As is known in the art, key pairs include a public key and a private key. The time interval can be a finite period of time, for example every second, 10 seconds, minutes or 10 minutes. The current time interval is referred to as t _n . In step 1020, it is determined whether a time stamp request was received during the time interval t _n . If no time stamp request was received during time interval t _n , the process returns to step 1010 to generate a new key pair for the next time interval, where n is incremented by one to indicate the next time interval.

If a time stamp request is received during the time interval t _n , in step 1030 the data appending the time stamp request is automatically signed. For example, conventional message summaries for data are generated to be automatically encrypted using a secret key of time interval t _n . As a result of signing the data, the sign of the time stamp can only be encrypted using the public key of the time interval t _n . At step 1040, a time stamp certificate is generated for delivery to the requestor indicating the temporary presence of data. In step 1050, it is determined whether additional time stamp requests are received within the time interval t _n .

If no additional time stamp request is received, the public key for time interval t _n is deleted at step 1060 and the process returns to step 1010 to generate a key pair for the next time interval and n is incremented by one. . If additional time stamp requests are received during the time interval t _n , the process returns to step 1030 to process each additional time stamp request. As indicated in step 1060, the secret key for time interval t _n is deleted at the completion of the time interval and the public key is stored for subsequent use, for example to decrypt the time stamp. Therefore, a separate secret key is used to automatically time stamp data associated with time stamp requests received for each defined time interval, according to one embodiment of the invention.

The process according to the embodiment of the present invention described in FIG. And the private key is deleted after a time interval. In contrast, conventional time stamp systems use a separate mechanism based on a computer system that uses a single secret key to sign all time stamp requests and executes a time stamp to provide time stamp data. Unlike a time stamping method according to one embodiment of the present invention, some conventional systems may be used to generate an encrypted message digest for time stamps as described, for example, in US Pat. No. 5,136,647, incorporated herein by reference. Chain together message summaries for signed sequentially submitted documents.

2A illustrates a flowchart for a digital time stamping method according to another embodiment of the present invention. In step 2010 a key pair is generated. As is known in the art, key pairs include a public key and a private key. According to an embodiment of the invention, a key pair is generated for each time interval used by the system implementing the time stamping method. Execution systems may include conventional general purpose computers such as, for example, microprocessor-based personal computers or servers. In an embodiment of the present invention, the method is implemented in software running on a client-server computer system architecture. The time interval can be any finite period of time, for example every second, ten seconds, minutes or every ten minutes. The current time interval is called t _n and the next time interval is called t _{n + 1} . For time stamping purposes of the document, accuracy in minutes is sufficient for subsequent authentication purposes.

In step 2020, another key pair is generated at time t _{n + 1} . Like the first key pair, the next key pair has a public key and a private key. To generate the key pair in steps 2010 and 2020, a conventional digital time stamping system such as PGP may be modified to automatically generate a key pair at defined time intervals. For example, a conventional digital time stamping system uses user I in the system to input the information needed to generate a key pair (e.g., pass phrase and random seed required by PGP). / O is configured to allow the user to generate a key pair. According to one embodiment of the present invention, the source code for such a system can be modified to generate pass phrases and random seeds that are automatically fed to the key pair generation algorithm for each finite time interval, thereby generating the key pair. It will automatically provide the input normally provided by the user to generate.

In step 2030, the public key of time interval t _{n + 1} is signed using the secret key of time interval t _n . For example, a conventional message digest for a public key of time interval t _{n + 1} is generated and encrypted using a secret key of time interval t _n . As a result of signing the public key of time interval t _{n + 1} , the sign of the public key can be decrypted using only the secret key of time interval t _n . By using a private key of the time interval t _n to sign the public key of the time interval t _{n + 1} is PGP software existing software, such as (for example, a command line to indicate that a key has been signed by another key) Can be achieved using the script-based control of. The secret key at time interval t _n is deleted. Therefore, the private key of the time interval t _n is present for the time required for the time interval t _{n + 1} to sign the public key of the duration of the time interval t _{n + 1} of the time interval t _n. In step 2050, the public key for the time interval t _n is stored for subsequent use to decrypt the time stamp, for example a public key of the time interval t _{n + 1.}

In step 2060 it is determined whether a time stamp request has been received for a time interval t _{n + 1} . If no time stamp request is received, the process returns to step 2020 to generate a key pair for the next time interval, where n is incremented by one. If a time stamp request is received during the time interval t _{n + 1} , in step 2070 described in FIG. 2B, the data appended to the time stamp request is signed using the secret key of the time interval t _{n + 1} . For example, as is known in the art, conventional message summaries for time stamped data according to embodiments of the invention are generated and encrypted using a secret key of time interval t _{n + 1} . As a result of signing the data using the secret key of the time interval t _{n + 1} , the sign of the time stamp can be decrypted using only the secret key of the time interval t _{n + 1} , and the public key itself is an embodiment of the present invention. Time stamp, and can be authenticated using the public key of the conventional time interval t _n as described above. Therefore, using an embodiment of the method according to the invention, the authentication of the time stamps on the data is voluntarily validated when the keys for the two time intervals are chained together. No independent third party is needed to verify that the time stamp for the data is correct. In another exemplary embodiment, the key pair for t _{n + 1} is generated and during the end of the previous time interval t _n to ensure that the key pair for time interval t _n is available immediately at the time of t _{n + 1} . Certified in advance

In step 2080, a stamp certificate is generated for delivery to the requesting party. According to an exemplary embodiment of the present invention, such a stamp certificate includes the digital signature of the authenticated public key for the submitted data and the time intervals t _n and t _{n + 1} . In step 2090 it is determined which additional time stamp request is received within the time interval t _{n + 1} . If no more time stamp requests are received within time interval t _{n + 1} , the process returns to point B in FIG. 2A to generate a key pair for the next time interval. If another time stamp request is received within time interval t _{n + 1} , the data appended with the time stamp request in step 2100 is signed using the secret key of time interval t _{n + 1} as described above and the process is no longer available. The process returns to step 2090 until no time stamp request is received within the time interval t _{n + 1} .

The method according to an embodiment of the present invention for time stamping data can be implemented, for example, as hardware wired logic using software, firmware, or a suitable general purpose computer. For example, the software execution of the present invention may be written in the Java programming language which can run on any platform.

3A illustrates an exemplary client-server architecture for implementing a time stamping method according to an embodiment of the present invention. In a client-server architecture, the server portion of the time stamping program for an embodiment of the present invention resides in memory 3015 of the server 3010, for example. The time stamping program is executed on the CPU 3016 connected to the memory 3015. The server 3010 is connected to the client 3030 via a connection 3030 such as, for example, a LAN, WAN or Internet connection. Client computer 3020 includes a time stamping client portion of a method according to an embodiment of the present invention residing in memory 3025, wherein the time stamping client program is executed on CPU 3026 connected to memory 3025. I / O device 3040, such as a keyboard or mouse, provides user access to a time stamping method according to an embodiment of the present invention.

In operation, for example, a user may have an I / O device 3040 that causes a client application stored in memory 3025 to execute in memory 3026 and generate a message digest for data in a manner known in the art. Identifies data that is time stamped through. Message summaries are sent to server 3010 via connections 3030, and applications stored in memory 3015 are executed in memory 3016 to time stamp message summaries, as described in Figures 1 or 2A-2B. Similarly, the time stamp certificate is restored to the client computer 3020 through the connection unit 3030.

In another implementation of the client-server architecture shown in FIG. 3A, signing occurs at the client computer 3020. For example, via I / O device 3040, a user submits a stamp request to server computer 3010 via connection 3030 without identifying the data to be time stamped and providing a message summary for the data. In response to the stamp request, server 3010 generates a key pair (e.g., the public key is signed by the secret key of the previous time interval key pair) for the current time interval in accordance with an embodiment of the present invention. And return the public key to the client computer 3020 from the key pair for the current time interval, the pass phrase for the secret key of the time interval, and the previous time interval. In order to ensure the confidentiality of the transmission from server 93010 to client 3020, connection 3030 may include a secure channel using, for example, a secure socket layer (SSL). When the client 3020 receives a transmission from the server 3010, the client generates a message digest and for example the message digest of the time stamp request using a secret key of the current time interval in a manner known in the art. Sign. After the time stamp is generated, the client-side copy of the associated secret key and pass phrase is deleted immediately.

In another embodiment of the client-server architecture shown in FIG. 3A, the client computer 3020 generates its own key pair and generates a server (s) to time stamp the public key of the key pair generated by the client computer 3020. Use the key pair generated by 3010. For example, client computer 3020 generates a key pair and sends the public key of the key pair to server 3010 via connection 3030. The secret key of the key pair generated by server 3010 for the current time interval is used to sign the public key from client 3020. The signed public key and the public key of the key pair generated by the server are sent back to the client 3020. Immediately after the time stamp is generated, the secret key from the key pair generated by the client 3020 is immediately deleted, and the client-side public key is server-side to issue a revocation certificate for the client-side public key. Canceled by using a private key. The private key from server 3010 is destroyed. The revocation certificate is incorporated into the time stamp certificate along with the signing of the data, the server side public key for the current and previous time intervals, and the client side public key.

3B shows another embodiment of a system for implementing a time stamping method according to an embodiment of the present invention. In FIG. 3B, the time stamping method is performed in a single computer system 3100, such as a relational data system or a fund trading system. Computer system 3100 includes a memory 3115 coupled to CPU 3116. I / O device 3140, such as a keyboard or mouse, is connected to computer 3100 and provides user access to a time stamping method according to an embodiment of the invention. Memory 3115 includes, for example, a time stamping program according to an embodiment of the present invention and a resident program to generate a message summary for the data to be time stamped.

According to the embodiment of FIG. 3B, a user identifies data to be time stamped via I / O device 3140, and the system automatically identifies data to be time stamped, for example in response to a database transaction. The identification of the data to be time stamped causes the resident program stored in memory 3115 to execute in CPU 3116 and generate a message digest for the data. The message summary is provided to an application stored in memory 3115, which is executed on CPU 3116 to time stamp the data and returns a time stamp certificate to the resident program, which returns the time stamp certificate to the user I / O. O device 3140.

Therefore, according to the present invention, key pairs are generated at specific time intervals and the time stamp request is automatically performed using the secret key for the time interval, which is destroyed after the time interval. In another embodiment of the present invention, a conventional time interval secret key is used to sign the secret key for the next time interval before the secret key of the previous time interval is destroyed. In this embodiment of the present invention, every time interval has its own key pair in which the secret key is destroyed after signing the public key for the next time interval. According to the present invention, the key pair should not be generated consecutively at each time interval, but is selected from a queue for each time interval at which a time stamp request is received.

The time stamping method according to an embodiment of the present invention firstly generates a key pair corresponding to a transient time interval that does not correspond to a fixed entity, such as using a previous system, and secondly, a key and a sign generated by the key. Public key cryptography is used as a new method to provide the mechanisms used and to provide a strict proof of the time of authentication and existence of content in the data signed by the system. As noted above, a feature of the system is that the secret key is limited for a certain time interval and typically exists only for a very short period and is replaced by the next key as the next time interval proceeds. Public key cryptosystems such as PGP with the above modifications are used to automatically generate a series of public key cryptographic key pairs at regular time intervals. Each key contains an assignment within the user ID of the key that identifies the particular time interval while in use. For a dynamically generated key, the minimum possible duration of the time interval is limited by the time required to use the key pair and generate the key pair to validate the public key. As noted above, short time intervals can be enabled by pre-generating key pairs.

As noted above, the accuracy of the time specification is evidenced by the "chain" of the sine, so that each new time interval's public key uses the previous key's private key just before deleting the previous key's private key. Authenticated (eg, digitally signed). This is done, for example, by using the secret key of the previous time interval to digitally sign the public key of the new time interval. Immediately after the public key is signed, the private key from the previous interval is deleted.

The public key of each key pair is stored for future use. Some predetermined secret key is used for time stamping data only for a time interval immediately following the interval at which the secret key was generated. During the use of the interval, the secret key is used to digitally sign and time stamp all denters submitted to the system for this processing. Once data is submitted to the system for time stamping, these data are processed by signing using the secret key for each time interval. This signing process generates a time stamp certificate. Each time stamp certificate includes, for example, a digital signature of the data generated by the public and private keys authenticated for use of the current time interval. The public key for each interval use can be stored for future reference. For future use in the easy authentication of time stamp certificates, all time stamp certificates can be well stored even if such time stamp certificates are not required for further proof of the accuracy of the time stamps generated by the system.

At the end of each time interval, a new key pair is generated, the public key of the new pair is authenticated (signed) by the private key of the current time interval, and the secret key is deleted and the cycle continues. At some later point, validating the time stamp requires using the public key at each time interval to authenticate the digital signature in the time stamp certificate. Validation of the public key is accomplished by using the public key of the previous time interval to sign the public key to be authenticated. The ability to track through the "chain" of a public key certificate sign provides undeniable evidence of the location of the stamp at any individual time interval within the sign chain. Further evidence of the exact time that a given time interval key is in use can be provided by tracking another certificate generated by the same key and collecting evidence of the time of signing and the signed data associated therewith. Since the secret key for each time interval is destroyed immediately after the time interval has passed, it will be impossible to generate a fake time stamp after that fact.

Many other time stamping methods according to embodiments of the invention are possible. As noted above, for example, a message summary can be calculated at the user's site and only the message summary sent to the server for signing. This ensures both efficient network bandwidth usage and data accuracy.

Claims (18)

Generating a key pair including a secret key and a public key at first time intervals; Receiving an authentication request; Automatically responding to the authentication request by digitally signing data associated with the authentication request using the secret key; And And deleting the secret key. 2. The method of claim 1, further comprising generating a time stamp certificate for verifying the digital signature of the data. 2. The method of claim 1, further comprising storing the public key of the first time interval. The method of claim 1, further comprising authenticating the digitally signed data using the public key. 2. The method of claim 1, further comprising determining whether additional authentication requests have been received during the first time interval. 6. The method of claim 5, further comprising automatically responding to the additional authentication request by digitally signing data associated with the additional authentication request using the private key for an additional authentication request, wherein the secret key deletion step is performed. Is performed after the further authentication request is answered. The method of claim 1, Generating a key pair comprising a secret key and a public key at a next time interval; Receiving a next authentication request; Automatically responding to a next authentication request by digitally signing data associated with a next authentication request using the secret key of the next time interval; And And deleting the secret key for the next time interval. Generating a first key pair comprising a first public key and a first secret key at a first time; Generating at a second time a second key pair comprising a second public key and a second secret key; Signing a second public key using the first secret key; Deleting the first secret key; Processing an authentication request during the first time interval using the second secret key; And And deleting the second secret key. 9. The method of claim 8, further comprising storing a first public key. 9. The data authentication method according to claim 8, wherein said authentication request processing step includes automatically responding to said authentication request by digitally signing data associated with said authentication request using said first private key. 11. The method of claim 10, further comprising generating a time stamp certificate for verifying the digital signature of the data. 12. The method of claim 11, wherein said time stamp certificate comprises a digital sign and a second public key. 13. The method of claim 12, wherein said time stamp certificate further comprises a first public key. 10. The method of claim 8, further comprising authenticating digitally signed data using the first public key. General purpose computer; And An I / O device coupled to the general purpose computer, the general purpose computer having a memory containing a program executable by the general purpose computer, The executable program is, Generate a key pair comprising a secret key and a public key in a first time interval, Receive an authentication request, Automatically respond to the authentication request by digitally signing data associated with the authentication request using the secret key, and Instructing the general purpose computer to delete the secret key. 15. The system of claim 14, wherein said general purpose computer has a client-server architecture comprising a client computer and a server computer. General purpose computer; And An I / O device coupled to the general purpose computer, the general purpose computer having a memory containing a program executable by the general purpose computer, The executable program is, Generating a first key pair comprising a first public key and a first secret key at a first time interval, Generating a second key pair including a first public key and a second secret key at a second time interval, signing a second public key using the first secret key, Process an authentication request during the second time interval using the first secret key, and Instructing the general purpose computer to delete the first secret key. 17. The system of claim 16, wherein said general purpose computer has a client-server architecture comprising a client computer and a server computer.