US5222140A — Cryptographic method for key agreement and user a…

Claim 1

Independent Claim 140 words

A method for enabling a user terminal i and a network access unit j in a communication system to choose a session key for a communication session comprising the steps of: at the start of a communication session, transmitting a public key from the network access unit to the user terminal via a communication channel, at the user terminal, utilizing an electronic device to select a number x and to perform a public operation on the number x utilizing the public key received from the network access unit, transmitting via said communication channel the result of said public operation from said user terminal to said network access unit, and at said network access unit, performing a secret operation on said result utilizing a secret key of the network access unit to invert said public operation to compute the number x.

Claim 2

Independent Claim 140 words

A method for enabling a user terminal i and a network access unit j in a communication system to choose a session key for a communication session comprising the steps of: at the start of a communication session, transmitting a public key from the network access unit to the user terminal via a communication channel, at the user terminal, utilizing an electronic device to select a number x and to perform a public operation on the number x utilizing the public key received from the network access unit, transmitting via said communication channel the result of said public operation from said user terminal to said network access unit, and at said network access unit, performing a secret operation on said result utilizing a secret key of the network access unit to invert said public operation to compute the number x.

Claim 3

Dependent Claim 13 words

The method of claim 1 wherein the number x is said session key.

Claim 4

Dependent Claim 45 words

The method of claim 1 wherein said public key of said network access unit includes a modulus N: and said secret key of said network access unit includes the prime numbers p j and q j , where N j =p j q j .

Claim 5

Dependent Claim 34 words

The method of claim 3 wherein said public operation is e 1 =x 2 mod N j where e 1 is said result, and said secret operation is x=√e 1 mod N j .

Claim 6

Independent Claim 137 words

The method of claim I wherein said user terminal has a secret key S i and a public key P i and wherein said network access unit has a further secret key S j and a further public key P j such that P j Si ≡P i Sj mod N, where N is a modulus and wherein said method further comprises the steps of transmitting P j to said user terminal, transmitting P i to said network access unit, evaluating at said user terminal η≡P j Si mod N and determining a session key sk=f(x,η) where f is an encipherment function, evaluating at said network access unit η≡P i Sj mod N and determining said session key sk=f(x,η) whereby both said network access unit and said user terminal are in possession of said session key sk.

Claim 7

Dependent Claim 22 words

The method of claim 1 Wherein said method further comprises the step of authenticating said user terminal at said network access unit.

Claim 8

Dependent Claim 101 words

The method of claim 6 wherein said step of authenticating said user terminal comprises transmitting from said user terminal to said network access unit a linkage including public identification information of the user terminal and an authentication certificate, which if legitimate, is the result of utilizing a secret certification key to perform a secret certification operation on a function of said linkage, and at said network access unit, utilizing a public certification key to perform a public certification operation to invert said secret certification operation and determining if the result of said inversion is identical to said function of said linkage.

Claim 9

Dependent Claim 22 words

The method of claim 1 wherein said method further comprises the step of authenticating said network access unit to said user terminal.

Claim 10

Dependent Claim 94 words

The method of claim 8 wherein said authenticating step comprises transmitting from said network access unit to said user terminal a linkage including public identification information of the network access unit, and an authentication certificate which is the result of utilizing a secret certification key to perform a secret certification operation on a function of said linkage, and at said terminal, utilizing a public certification key to perform a public certification operation to invert said secret certification operation and determining if the result of the inversion is identical to said function of said linkage.

Claim 11

Dependent Claim 40 words

The method of claim 1 wherein said user terminal is a portable telephone of a portable communication system, said communication channel is a radio link, and said network access unit is a port control unit of said portable communication system.

Claim 12

Dependent Claim 14 words

The method of claim 1 wherein said public operation is a one-way trapdoor function.

Claim 13

Independent Claim 197 words

A method for enabling a user terminal and a network access unit in a communication system to choose a session key for a communication session comprising the steps of at the start of a communication session, transmitting via a communication channel from a network access unit to a user terminal a modulus N j , N j =p j Q j , where p j and q j are large prime numbers known only to the network access unit j, utilizing an electronic device at the user terminal to select a number x and to evaluate a quantity e 1 =y(x) mod N j , where y(x) is a function which is hard to invert without knowledge of the factors p j and q j , transmitting via said communication channel the quantity e 1 from said user terminal to said network access unit, at said network access unit, determining x=y -1 (e 1 ) mod N j , whereby the number x is now known to said user terminal and said network access unit, and utilizing said number x as a session key to send encrypted messages between said user terminal and said network access unit.

Claim 14

Independent Claim 197 words

A method for enabling a user terminal and a network access unit in a communication system to choose a session key for a communication session comprising the steps of at the start of a communication session, transmitting via a communication channel from a network access unit to a user terminal a modulus N j , N j =p j Q j , where p j and q j are large prime numbers known only to the network access unit j, utilizing an electronic device at the user terminal to select a number x and to evaluate a quantity e 1 =y(x) mod N j , where y(x) is a function which is hard to invert without knowledge of the factors p j and q j , transmitting via said communication channel the quantity e 1 from said user terminal to said network access unit, at said network access unit, determining x=y -1 (e 1 ) mod N j , whereby the number x is now known to said user terminal and said network access unit, and utilizing said number x as a session key to send encrypted messages between said user terminal and said network access unit.

Claim 15

Dependent Claim 155 words

The method of claim 12 wherein said method further comprises the steps of utilizing an electronic processor comprising part of said user terminal to generate a plain text message m which includes i and c i where i is an identification number of said user terminal and c i is a certificate of said user terminal, encrypting said plain text message m at said user terminal utilizing an encipherment function f to obtain an encrypted message e 2 =f(x,m), transmitting said encrypted message e 2 via said communication channel from said user terminal to said network access unit, and authenticating that the user terminal is a legitimate user of said communication system by decrypting said message e 2 and determining if c i 2 mod N u equals g(i), where N u is a certification modulus and g(i) is a one way function which expands its argument to the size of the modulus N .

Claim 16

Dependent Claim 107 words

The method of claim 12 wherein said method includes authenticating said network access unit to said user terminal by the steps of at the start of said communication session, transmitting from said network access unit to said user terminal, in addition to said modulus N j , a certificate c j of said network access unit and the identification number j of the network access unit, and authenticating said network access unit at said user terminal by utilizing an electronic processor comprising part of said user terminal to determine if h(j,N j ) equals c j 2 mod N u , where h is a hashing function.

Claim 17

Dependent Claim 32 words

The method of claim 12 wherein y(x) mod N j equals x 2 mod N j and y -1 (e 1 ) mod N j equal √e 1 mod N j .

Claim 18

Dependent Claim 29 words

The method of claim 15 wherein said number x is utilized by said user terminal and said network access unit to determine a session key for said communication system.

Claim 19

Dependent Claim 38 words

The method of claim 12 wherein said communication system is a portable communication system, said user terminal is a portable telephone, said communication channel is a radio link, and said network access unit is a port control unit.

Claim 20

Independent Claim 160 words

A method for enabling a user terminal and a network access unit in a communication system to choose a session key for a communication session comprising the steps of: at the start of a communication session, transmitting via a communication channel from the network access unit to the user terminal a public key of said network access unit, at said user terminal, utilizing an electronic processor to select a number x and to generate a quantity e 1 =y(x) where y(x) is a function that is evaluated utilizing said public key and that is hard to invert without knowledge of a secret key known only to said network access unit, transmitting via said communication channel said quantity e 1 from said user terminal to said network access unit, and at said network access unit, determining x=y -1 (e 1 ) utilizing said secret key, whereby said number x is now known to said user terminal and said network access unit.

Claim 21

Independent Claim 160 words

A method for enabling a user terminal and a network access unit in a communication system to choose a session key for a communication session comprising the steps of: at the start of a communication session, transmitting via a communication channel from the network access unit to the user terminal a public key of said network access unit, at said user terminal, utilizing an electronic processor to select a number x and to generate a quantity e 1 =y(x) where y(x) is a function that is evaluated utilizing said public key and that is hard to invert without knowledge of a secret key known only to said network access unit, transmitting via said communication channel said quantity e 1 from said user terminal to said network access unit, and at said network access unit, determining x=y -1 (e 1 ) utilizing said secret key, whereby said number x is now known to said user terminal and said network access unit.

Claim 22

Dependent Claim 24 words

The method of claim 18 wherein said number x is utilized as a session key by said user terminal and said network access unit.

Claim 23

Dependent Claim 24 words

The method of claim 18 wherein said method includes the step of authenticating the identity of said user terminal to said network access unit.

Claim 24

Dependent Claim 24 words

The method of claim 18 wherein said method includes the step of authenticating the identity of said network access unit to said user terminal.

Claim 25

Dependent Claim 32 words

The method of claim 18 wherein y(x) equals x 2 mod N, N=p.q, where N is said public key, and p and q are large prime numbers which form said secret key.

Claim 26

Dependent Claim 38 words

The method of claim 18 wherein said communication system is a portable communication system, said communication channel is a radio link, said network access unit is a port control unit and a user terminal is a portable telephone.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1996-06-21	1996-12-21	1997-06-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2000-06-21	2000-12-21	2001-06-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2004-06-21	2004-12-21	2005-06-22	$7700.00	Window Closed / Lapsed

Cryptographic method for key agreement and user authentication

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