KR20030061558A - User authentification using a virtual private key - Google Patents

Abstract

PURPOSE: A method for authenticating an user by using a private key is provided to authenticate the user by using a digest in a registration process and an authentication process. CONSTITUTION: A private key of an user is obtained from the user(910). An encryption key is obtained from a client side related to the user and the encryption key is decoded by using the private key(920). A preliminary digest is calculated by using a time stamp, an user authentication serial number, and an encryption key of a client(930,940). An encryption key of an encoded server is obtained from a non-encoded message including the time stamp, the user authentication serial number, and the encryption key and the encryption key of the encoded server is decoded by using the private key(975). The calculated digest is calculated by using the time stamp, the user authentication serial number from the non-encoded message(980). The message is authenticated by comparing the calculated digest to the preliminary digest(985-992).

Description

User Authentication using Virtual Private Key {USER AUTHENTIFICATION USING A VIRTUAL PRIVATE KEY}

First, the present invention relates to a method for providing strong authentication using a PKI. The present invention also relates to a software program that enables user authentication using a virtual private key in a computer system. The present invention further relates to a computer system in which user authentication is performed using a virtual private key.

Secondly, the present invention relates to a method for providing strong user authentication in a magnetic swap card or a biometric device. The present invention also relates to a software program that enables user authentication in a magnetic swap card or biometric device performed in a computer system. The present invention further relates to a computer system in which user authentication is performed using a magnetic swipe card or biometric device.

Third, the present invention relates to a method for providing strong user authentication using pass phrases. The invention also relates to a user authentication software program using pass phrases in a computer system. The invention further relates to a computer system in which user authentication is made using pass phrases.

2. Related Technology

PKI system authentication today is based on the fact that a user knows a private key. However, the private key is not something that the user can remember or enter directly. Therefore, in general, the private key is encrypted and stored in the computer and used by the user's password input. But the problem is that password entry is the weakest method of security. The passwords that users can remember can be easily found by smart intruders and hackers. Therefore, PKI technology today is considered to have a weak connection problem because private keys are only protected by passwords.

Another problem is that PKI systems are not readily available in certain environments with limited storage space. The digital signature used by the PKI system to authenticate the sender is a message. At least 2000 bytes are required for digital signatures based on 1024-bit keys. In certain cases, however, storage space limitations prevent direct PKI technology (especially digital signatures). An example of this particular environment is a magnetic swap card. Credit cards and other magnetic swap cards do not have more than 2000 bytes of storage. Another example is in the remote access protocol. The client station does not communicate directly with the security server. Instead, the client station communicates with a communication server. Remote access protocols are used for communication between client stations and communication servers, which are generally designed to obtain a user ID and password from the user. A common example of such a protocol is the PPP protocol. This user ID / password is based on the protocol being able to send 60 bytes in the user ID / password field. However, this is a public key technology that is not enough space for user authentication, encryption, or digital signatures. Therefore, PKI authentication cannot be effectively used in remote access systems.

To overcome the weak connection problem, two-factor technology has been developed. The dual element is the combination of what the user knows (e.g. a password) and what the user has (e.g. a magnetic swipe card, fingerprint, etc.). Dual element technology provides very strong security but requires additional hardware devices. The equipment needed for this is usually not built into a computer system and is a problem for users working on workstations without such equipment. Thus this dual element technique is not a desirable solution.

Therefore, there is a need for a method for solving a weak connection problem of security that is performed only with a password and for strong user authentication without requiring additional hardware. There is also a need for a way to apply PKI technology to an environment with limited storage space.

The present invention solves the problem defined above by using digest in two stages of registration and authentication.

First, user authentication is performed using PKI technology in an environment with limited storage space. Magnetic swap card systems have limited storage space. In remote access systems (phone lines), the user ID / password field is limited in size. The present invention is useful in environments where this kind of storage space is limited. In the present invention, a special conversation method is used to apply a PKI technique so that user authentication can be performed without transmitting a long key. The method includes the technique of mapping a full length private key field area into a relatively short data field.

In applying the techniques of the present invention to a remote access environment, the present invention uses conventional registration and authentication steps.

The present invention applies a PKI using a virtual private key in order not to transmit the actual PKI key and authentication serial number or digital signature.

First, the present invention is a method for providing authentication of a user message using a PKI technology in an environment in which a storage space is limited in a computer system or a computer software program and thus a direct PKI technology cannot be used. Once registered, PKI technology is used without the actual transmission of long keys, authentication serial numbers, or digital signatures. The private key is used to authenticate the user at the client station and retrieve the encrypted secret key that was stored. The digest is calculated using the secret key, the user's X.509 ISO standard public key certificate serial number, and a time stamp. Use the user authentication serial number to reduce the size of the message. The digest, combining the user authentication serial number and the time stamp, creates a concise message that is sent using the user ID / password field in the remote access protocol. No private or private key is sent. The secret key already stored on the security server is used to calculate the digest, along with the serial number and time stamp of the user authentication, and compares the digest with the digest. If the two digests match, the user is considered authenticated. Time stamps are intended to prevent replay attacks.

Secondly, the present invention provides a method of using some information named a reference instead of a user's private key. Basically, this item differs in that the first item requires the user's private key only once during the user registration process. So instead of using the user's private key, use the reference read from what the user has, such as a magnetic swipe card or biometric device. The reference is simplified to be used as the client's private key. A preliminary digest is made using the user authentication serial number and the time stamp secret key. This preliminary digest is sent to the authentication server with the user authentication serial number and time stamp. The authentication server stores the references themselves or in digest form. The digest type reference is used as the server's private key. Authentication is accomplished by using the time stamp, user authentication serial number, and secret key to calculate the digest and comparing it to the preliminary digest received. The advantage of this item is that no references are stored on the client. A hacker cannot hack a client station to get a reference. In addition, the user's private key is not used after registration. Also, if the user has a magnetic swap card or the like, the user can easily find the card lost. Instead of a magnetic swap card, you can use a fingerprint, retina scan, or the like as a reference. Also, the reference itself is sent only once during the registration process, after which it does not exist on the network.

Third, the present invention uses a pass phrase as a way to replace the reference. That is, the third item differs only in that the second item requires what the user has. The user only needs to remember and use the pass phrase to be used as a reference. Like the reference, the pass phrase is not stored on the client station. In the second section, the user private key was used only during the registration process and thereafter it did not exist on the network. In addition to the third item, no additional card reader or biometric device is required. Just type in a phrase on the keyboard. The description will be more clearly understood with reference to the accompanying drawings.

Figure 1: Access to a security server on network security

Figure 2: Use of public and private keys in PKI systems

Figure 3: Public Key Reference Table

Figure 4: How to digitally sign a message

Figure 5: Method for authenticating a digital signature included in a message

Figure 6: Flow chart of a method for generating and authenticating a digital signature

Figure 7: Remote access environment diagram

Figure 8: Registration procedure using virtual private key

Figure 9: Authentication procedure using virtual private key

Figure 10: Registration procedure using reference or pass phrase

Figure 11: Authentication procedure using reference or pass phrase

The items mentioned here are described in detail. First, the remote access environment, and then the magnetic swap card environment, and finally the pass phrase. Many descriptions are attached to the above three items, which are intended for understanding the present invention.

Item for remote access environment

Before describing the present invention with respect to the remote access environment, the background principle related to the present invention will be described. The approach to a secure server, the use of public and private keys in PKI, and digital signatures. Security is one of the serious problems in today's popular world. An important aspect of network security is user authentication. User authentication includes verifying a user's uniqueness in initializing a session or other activity, or preventing unauthorized duplication of a user who has already been verified. In dealing with security, the industry has adopted a secure server approach. This approach is achieved by the security server intermediary between the client and the application server. The role of the security server is to provide a single connection between the client and the application server. The secure server establishes communication between the client and the application server only if the user is authenticated. In this article, the term security server refers to an incompass security server, proxy server, firewall, and authentication server.

Secure Server Approach

Figure 1 illustrates the security server approach. It is a very simplified picture. 10 means client. A client can be understood as a process running on a general purpose computer system or a special purpose computer system. As a process, the client also represents a user who wants to run an application over the network. The number 20 in Fig. 1 represents a security server. 30 represents an application server. 10 and 30 cannot communicate directly. 20 mediates both between 10 and 30. The security server 20 can be understood as a process running on a general purpose computer or a special purpose computer system. 30 can also be described as similar.

More specifically, when a user tries to do something on the network using client 10, 20 establishes a communication connection with 30. But in the middle 20 requires some form of security. In other words, it handles the authentication of the user using the client. Therefore, only authenticated users can communicate with 30.

Typically, 10, 20, and 30 run on separate computer systems located at considerable distances. Even if this is the case, the method used here is true even if 10, 20, and 30 are running on the same computer system.

PKI technology

To protect privacy in communications, a system known as the public key infrastructure (PKI) has been developed. In a PKI system, either party or user has two encryption keys. The two cryptographic keys are the public key and the private key. A public key is a key that is open to all other users and a private key is a key that should never be revealed to other users.

2 shows that the user party is the sender and the user is the receiver. User wants to send a message to user from PKI system. In a PKI system, a user has a public key and a private key.

Figure 3 shows the tables available to the user in the PKI system. There is a table that is not exactly the same but is represented in Figure 3 with similar meaning. 300 is a public key table. The public key table contains information about each user, authentication serial number, username, and public key. The authentication serial number is typically the only number used to identify a particular user. Usernames use a combination of letters and numbers, which are commonly used to easily identify users. An example of a public key is 1024 bits.

Returning to Figure 2, User A has a message m, which is sent to User. The user acquires the public key of the user through the public key table of FIG. The encrypted message is then obtained through the encryption process of 240 with the obtained public key. The encrypted message is in a form suitable for transmission named txm.

The transmitted txm undergoes a decoding process of 250. Here we use-private key. The private key is known only to the user. The message m from the decryption process of 250 is the same as the message before the user encrypts it, unless it is changed in the middle. The encrypted message txm is encrypted using a-public key, which is completely indecipherable unless decrypted with a-private key. Thus, the encrypted message txm can be sent on the network without fear of being read by an unauthorized intruder.

It is not necessary to have a public key table such as the table of FIG. Rather than looking for the user's public key in the public key table, the user does request the user's public key from the network. The public key is public and the user can freely distribute the public key.

Therefore, in the PKI system, the sender encrypts the message with the public key of the receiver and the encrypted message is sent to the receiver. The receiving side receiving the encrypted message can decrypt the encrypted message using the receiving party's private key.

Even if the message sent to the user is sent safely without interference from an unauthorized intruder on the network, the user cannot confirm whether the message was originally sent. Instead of sending a message from the user's head, a message from the user's bottle disguised as the user's head may be sent. Therefore, user bottle (thief) is the user's case to user (bank). I ask you to transfer my account right away to your account. Message can be sent encrypted with the user-public key. The successful decryption of a sent message by the user does not mean that the message sent is from Ab.

Electronic signature

The PKI system uses digital signatures to verify who sent the message. That is, it confirms that the message is sent by the user by using the electronic signature attached to the message and ensures that there is no change of the message when the electronic signature is made.

Figure 4 shows the leaflet associated with the digital signature. The first step, 410, creates a digest for the message to be sent. Digest is a familiar concept for people in this field, but to explain it is a numerical result similar to a hash function or checksum. This numerical result for a message is called a message digest. The result of 410 is the calculated digest or cd. Cd is input to 420 and encrypted with the sender's private key. That is, the result of 420 is an encrypted digest, or ed. In step 430, the encrypted digest and the unencrypted message m are combined. The combined results are shown as ed + m. In step 440, txm is generated by encrypting ed + m with the public key of the receiver. That is, txm includes the original message of the sender and the electronic signature of the sender of the message.

5 is a flowchart illustrating a process of decoding txm. The encrypted txm is decrypted using the private key of the receiver in step 510. The result is ed + m. In step 520, ed + m is separated into ed and m, respectively. In step 530, the sender is identified from the unencrypted message m. The confirmed sender is used by the same means as described in step 550. In step 540 the content of the unencrypted message is used to calculate the message digest. The result of this step is cd. In step 550, it is assumed that the public key of the sender is obtained. In step 530, the sender's public key can find out the sender through the message and the contents included therein, and can refer to the public key table as shown in FIG. The public key is used to decrypt ed in step 560 to obtain the decrypted digest dd. Comparing cd and ed in step 570, if the two digests match, the message is assured that the message was sent from the sender and that there was no change in content (590). If the values of cd and ed do not match, it means that either the message was not sent from the sender or the contents of the message were changed during transmission (580). As described above, a method of verifying and authenticating a sender is called an electronic signature.

Figure 6 shows how the electronic signature is made between the user and the user. Each item has already been described. The former-private key shown here represents the private key of the former. For the sake of simplicity, the result of comparing step 570 with cd and dd is represented by r. In practical application, the authentication guarantee of public key table should be preceded. There must be a third party, called a trusted certification body. In order for digital signatures to be commonly accepted, a public key authentication form called the ISO X.509 standard is used. According to the X.509 standard, authentication requires the following fields: (A) Certificate serial number, (b) Certificate validity period, (c) Certificate-related name, (ㄹ) Owner's name of public key, (ㅁ) Owner's public key, (ㅂ) (a)-(ㅁ) Digital signature of the certification body for the information

Thus, X.509 authentication combines a user's name and his public key with the certificate authority's digital signature. This electronic signature ensures that the public key has not been changed since the time it was signed.

The certification body usually provides a certificate revocation list in its public key table. The revocation list is a list of revoked certification serial numbers. This list is certified and updated by the certification body.

Remote access

Side of the above-described remote access will be described in detail with reference to FIG.

In FIG. 7, the client 110 communicates with the security server 120 using a remote access method such as a telephone line. If the client cannot communicate directly with the security server 120, the client communicates with the 120 through the communication server 700. In general, the client 110 communicates with the communication server 700 through the communication link 710. This link is called the telephone line link. In the communication protocol, 710 is a remote access protocol (RAP) such as PPP. The communication server 700 and security server 120 are linked by other protocols such as TACACS or RADIUS.

See the following documents for a detailed description of TACACS and RADIUS.

internet RFC 1492, "An Access Control Protocol, Sometimes called TACACS", July 1993

internet RFC 2138, "TXT Remote Authentication Dial in User Service (RADIUS)", January, 1997

Enrollment

The present invention relates to the authentication process performed in the registration process. The registration process will be described with reference to FIG. In FIG. 8, 110 denotes a client 700, a communication server 120, and a security server. The user using the client 110 first requires a communication connection with the 700 in order to communicate with the 120. The communication server finds out where the security server 120 corresponds to the request and asks the user to enter a user ID and password. If ID and password are entered normally, communication server establishes connection between client and security server. Once a connection is established between a client and a secure server, it can send and receive data of any length between them. Communication server 700 does not play a role here. This is what is done in step 810.

The security server 120 sends the user authentication serial number to the client 110 in step 820. This serial number makes it easy for the client 110 to find the public key of the security server from the public key table.

In step 830, the user inputs his private key to the client. The private key can be manually entered, such as a magnetic swap card, fingerprint, token or retina. In step 840, the client uses the PKI technology.

Generate a random, random secret key.

In step 850, the client encrypts the generated private key with the user's public key and stores it in the client. The stored secret key can be decrypted only with the private key of the user.

In step 860, an electronic signature and message prepared with the user's private key are prepared. This message is combined with the secret key and the user authentication serial number in step 840. These two items become the message m, where we add the digital signature ed. Therefore, the txm encrypted with the public key of the security server is transmitted from the client 110 to the security server 120.

In step 870, the security server 120 decrypts txm using its own private key to obtain a digital signature from the message m and client ed having the client's secret key and the client's user authentication serial number. Authentication is performed in the same manner as described in FIG. From the server's point of view, the secret key is considered the sent secret key.

In step 880, the security server encrypts and stores the user's user authentication serial number and secret key. For efficient retrieval, they are stored in a table called an authentication table.

The security server checks the validity of the user's user authentication serial number at this point, verifies the digital signature, and checks the validity period by referring to the revocation list.

The registration process only needs to be done once. However, this must be done during the first phase of authentication. We say that we store the registered private key on the server, which can be stored anywhere the server can refer to it without necessarily being stored on the server device. In terms of performance, it is desirable to have many registered secret keys on the server side.

Registration Procedure Next, the authentication procedure is described.

certification

The authentication procedure is performed every time a user opens a session of a communication server or accesses an application server through a secure server.

Referring to FIG. 9, the user inputs his or her private key at the client in step 910. The client obtains the secret key already stored using the user's private key input in step 920 and decrypts it.

In step 930, a user authentication serial number and a secret key of the current time stamp user are collected to form a preliminary message. In step 940, a digest of the preliminary message is calculated. A spare message is never sent. The reason for generating the preliminary message is to make a digest. The algorithm used to create the digest in step 940 uses MD5 or SHA1. The generated digest is a size that can be put in the user ID / password field of the remote access protocol. This digest is a digest made from the preliminary message and will be called a preliminary digest. In step 950, a message to be actually transmitted is prepared. This message will be called a transport message to distinguish it from the spare message. The outgoing message consists of the user authentication serial number, the time stamp used to make the preliminary digest, and the preliminary digest. All three of these items are small enough to fit into the User ID / Password field of a remote access protocol such as PPP. In step 960, the transmission message is sent to the communication server in the user ID / password field. In step 970, the security server receives the transmission message data, classifies the correct part in the message composition, and obtains the user authentication serial number, time stamp, and preliminary digest. In step 975, the security server obtains an encrypted secret key from the storage device using the user authentication serial number. The private key is then decrypted using its private key. In step 980, the security server calculates a digest using the user authentication serial number, time stamp, and secret key obtained from the storage device. In step 985, the security server compares the calculated digest with the preliminary digest. The two digests only exist if the secret key included in the transmitted message is the same as the user's private key obtained from the security server. Thus, the user's private key is encrypted with the user's public key before being stored on the client, which means that it can only be decrypted with the user's private key. In step 990, the security server defends against the retransmission attack by comparing the time stamp received with the time stamp of the most recently received message. The advantage of step 990 is that the message sent is valid only once. It protects against replay attacks by storing a time stamp of each individual user's most recent message. In step 992, the user authentication serial number is valid in the security server 120.

The secret key is sent only once and sent from the client to the server in encrypted form. This process occurs only during the registration process. However, the secret key is used each time on both the client and the secure server during the authentication process. Therefore, we will call this private key the most private key. This is because it is often used but no transmission occurs during authentication. This has the advantage that the PKI technique can be used without transmitting long keys. Its short message length makes it ideal for small data fields. The inventive invention is a method of mapping long PKI information into small data fields.

However, the present invention is not limited to only the remote access environment. The present invention is applicable to any environment that transmits long PKI information.

Magnetic Card Environment

This section of the invention relates to the use of industry standard magnetic strip cards, also known as swap cards. These cards have limited storage space. The small amount these cards have can be thought of as having a small data field, such as a user ID / password field, in a remote access environment. In both cases, the virtual private key approach of the present invention is suitable in terms of the need for security and the transfer of larger data than the storage space.

Enrollment

A description with reference to FIG. There is no communication server 700 in FIG. In operation 810, the user at the client side requests a communication connection with the security document 120. A communication link is then established between 110 and 120. In step 820, the security server transmits its user authentication serial number to the client 110. In step 1030, the client reads the magnetic card to obtain the stored information. The information read is expressed as 'reference'. This reference is computed as a digest in step 1040, which is used as a secret key. In step 830, the user enters his or her private key on the client. The private key can be entered in any form (magnetic card, manual input). The secret key is not stored on the client or stored in the reference. In step 860, a message is prepared with an electronic signature made of the user's private key. The message contains a secret key and a user authentication serial number. This message is encrypted with the security server's public key and sent to the security server. In step 870, the security server 120 decrypts with its own private key and obtains a message, a secret key, a user authentication serial number, and an electronic signature. Security server 120 checks the validity of the user authentication serial number at this point. In step 880, the security server stores the encrypted secret key in the user authentication serial number. This information is stored in the authentication table.

Importantly, the contents of the magnetic card are never transmitted. Only the digest of the card is sent. Therefore, no user's credit card number or any other personal information exists on the network.

You don't need the user's private key that you needed during the registration process in the previous section, so a magnetic card or similar limited storage space is sufficient.

certification

A description with reference to FIG. In step 1110, the client process 110 receives information from the user's magnetic card. The information read from the card will be called a reference. The client computes the digest of the reference love and uses it as the secret key. In step 930, a preliminary message is prepared. The preliminary message includes a user authentication serial number, a current time stamp, and a user's private key. This preliminary message is never sent. In step 950, a transmission message is prepared. The transmission message prepared in step 950 is a user authentication serial number, a time stamp used when creating a preliminary message, and a digest of the preliminary message. In step 1160, the transmission message is sent to the security server. Steps 970-992 are the same as described for the remote access environment.

During registration, the secret key is encrypted and sent only once from the client to the server, but this secret key is used every time during the authentication process. This key is used every time, but not through the actual communication line. The important point here is that the user's private key is not required during the authentication process.

Invention for using pass phrases

Explain the pass phrase mentioned in section 3. A pass phrase is something that a user memorizes. This can be thought of as 'reference'. But this 'reference' is based on the user's memory, not the information from the magnetic card or biometric device. This passphrase means a relatively long phrase that can secure security that relies on short passwords.

The third item I'm going to explain is exactly the same as the magnetic card environment already described. In order to simplify the description, there are not many duplicate descriptions.

Enrollment

The registration process is shown in FIG. The only difference here is that the 'reference' does not come from the device (card reader, biometric device, etc.) but rather the pass phrase that the user remembers.

certification

The authentication process is shown in FIG. It is exactly the same as the second point.

The present invention solves the problem defined above by using digest in two stages of registration and authentication.

First, user authentication is performed using PKI technology in an environment with limited storage space. Magnetic swap card systems have limited storage space. In remote access systems (phone lines), the user ID / password field is limited in size. The present invention is useful in environments where this kind of storage space is limited. In the present invention, a special conversation method is used to apply a PKI technique so that user authentication can be performed without transmitting a long key. The method includes the technique of mapping a full length private key field area into a relatively short data field.

In applying the techniques of the present invention to a remote access environment, the present invention uses conventional registration and authentication steps.

The present invention applies a PKI using a virtual private key in order not to transmit the actual PKI key and authentication serial number or digital signature.

First, the present invention is a method for providing authentication of a user message using a PKI technology in an environment in which a storage space is limited in a computer system or a computer software program and thus a direct PKI technology cannot be used. Once registered, PKI technology is used without the actual transmission of long keys, authentication serial numbers, or digital signatures. The private key is used to authenticate the user at the client station and retrieve the encrypted secret key that was stored. The digest is calculated using the secret key, the user's X.509 ISO standard public key certificate serial number, and a time stamp. Use the user authentication serial number to reduce the size of the message. The digest, combining the user authentication serial number and the time stamp, creates a concise message that is sent using the user ID / password field in the remote access protocol. No private or private key is sent. The secret key already stored on the security server is used to calculate the digest, along with the serial number and time stamp of the user authentication, and compares the digest with the digest. If the two digests match, the user is considered authenticated. Time stamps are intended to prevent replay attacks.

Secondly, the present invention provides a method of using some information named a reference instead of a user's private key. Basically, this item differs in that the first item requires the user's private key only once during the user registration process. So instead of using the user's private key, use the reference read from what the user has, such as a magnetic swipe card or biometric device. The reference is simplified to be used as the client's private key. A preliminary digest is made using the user authentication serial number and the time stamp secret key. This preliminary digest is sent to the authentication server with the user authentication serial number and time stamp. The authentication server stores the references themselves or in digest form. The digest type reference is used as the server's private key. Authentication is accomplished by using the time stamp, user authentication serial number, and secret key to calculate the digest and comparing it to the preliminary digest received. The advantage of this item is that no references are stored on the client. A hacker cannot hack a client station to get a reference. In addition, the user's private key is not used after registration. Also, if the user has a magnetic swap card or the like, the user can easily find the card lost. Instead of a magnetic swap card, you can use a fingerprint, retina scan, or the like as a reference. Also, the reference itself is sent only once during the registration process, after which it does not exist on the network.

Third, the present invention uses a pass phrase as a way to replace the reference. That is, the third item differs only in that the second item requires what the user has. The user just needs to remember and use the passphrase for reference. As with references, pass phrases are not stored on the client station. In the second section, the user private key was used only during the registration process and thereafter it did not exist on the network. In addition to the third item, no additional card reader or biometric device is required. Just type in a phrase on the keyboard.

Claims (1)

Claim 1. What constitutes authentication 1) Obtaining the user's private key from the user 2) Obtaining an encrypted secret key from the client side associated with the user 3) decrypting the encrypted user secret key using the user's private key 4) Time stamp, calculating the user's user authentication serial number using the client's private key 5) use of unencrypted messages including time stamp, user authentication serial number, and preliminary digest; 6) Obtaining the encrypted server's secret key corresponding to the user authentication serial number from an unencrypted message. 7) Decrypting the encrypted server's secret key using the server's private key 8) Compute the calculated digest using the secret key obtained from the time stamp and user authentication serial number in the unencrypted message. 9) Authenticate the message by comparing the calculated digest with the preliminary digest Claim 2. In addition to 1 authentication method 1) generating a secret key 2) encrypting the client's private key with the user's public key and providing an encrypted private key 3) decrypting the encrypted secret key in the message using the server's private key 4) storing the secret key of the client and storing the secret key together with the corresponding user authentication serial number on the server Claim 3. How the server authenticates messages sent from users on the client 1) storing the client secret key associated with the user on the server with the user authentication serial number 2) Calculate the preliminary digest to be sent to the server using the time stamp, client secret key and serial number. 3) Sending the time stamp, user authentication serial number, and preliminary digest to the server 4) Calculate the digest from the message received from the server using the user authentication serial number, time stamp, and client secret key. 5) Authenticate the message by comparing the preliminary digest with the calculated digest Claim 4. In addition to 3, authentication method on server 1) encrypting the client's private key with the server's public key and storing it on the server 2) storing the secret key together with the user authentication serial number;