Method for enabling users of a cryptosystem to generate and use a private pair key for enciphering communications between the users
First Claim
1. A method for enabling users of a cryptosystem to generate and use a private pair key for enciphering communications between the users, comprising the steps of:
- for each user and each trustee of a group of at least two trustees, having at least one user individual key;
for each user, storing at least some of the user'"'"'s individual user keys in a physically-secure device;
having each of the users compute the private pair key in a physically-secure device from information that includes information stored in the user'"'"'s physically-secure device and identifying information of the other user, wherein the private pair key cannot be computed by a subset of of trustees containing less than a given number of trustees;
having one of the users generate a ciphertext using the private pair key; and
transmitting the ciphertext from the user to another user of the cryptosystem.
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Abstract
The present invention describes a method for enabling users of a cryptosystem to agree on secret keys. In one embodiment, a trusted agent chooses at least one individual key for each user, with at least a portion of such individual key being secret. At least some of the individual keys are then stored in physically secure devices, and the pair of users i and j use their individual keys to compute a common secret key. In another embodiment, each trustee of a group of trustees choose at least one individual key for each user, with at least some portion of such individual key being secret. The keys chosen by a sufficiently small number of such trustees, however, are insufficient for computing the common secret key of the users. Other hardware and software key exchange protocols based on these two techniques are also disclosed.
314 Citations
25 Claims
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1. A method for enabling users of a cryptosystem to generate and use a private pair key for enciphering communications between the users, comprising the steps of:
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for each user and each trustee of a group of at least two trustees, having at least one user individual key; for each user, storing at least some of the user'"'"'s individual user keys in a physically-secure device; having each of the users compute the private pair key in a physically-secure device from information that includes information stored in the user'"'"'s physically-secure device and identifying information of the other user, wherein the private pair key cannot be computed by a subset of of trustees containing less than a given number of trustees; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to another user of the cryptosystem. - View Dependent Claims (2, 3)
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4. A method for enabling users of a cryptosystem to generate and use a private pair key for enciphering communications between the users, comprising the steps of:
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generating at least one public key for each user by iterating at least a conventional one-way function on at least one private value stored in a physically-secure device; using the physically-secure device of each of a pair of users to compute the private pair key for the pair of users, wherein the private pair key is computed based on information that includes one user'"'"'s private information and the other user'"'"'s public key; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (5)
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7. A method for enabling users of a cryptosystem to generate and use a private pair key enciphering communications between the users, comprising the steps of:
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for each user and each trustee of a group of trustee of a group of trustees, generating at least one public key by iterating at least a conventional one-way function on at least one private value stored in a physically-secure device; having at least one of the two users use a physically-secure device to compute the private pair key from information that includes private information of the user and the other user'"'"'s public key, wherein a subset of trustees containing less than a given number of trustees does not possess any useful information for reconstructing the private pair key; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (8)
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9. A method for enabling two users of a cryptosystem to generate and use a private pair key to encipher communications between the two users, comprising the steps of:
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for each user and each trustee of a group of trustees, having at least one individual user key; having at least one of the two users receive and store in a physical device at least a public pair key for the two users; having at least one of two users use the physical device to compute the private pair key from information that includes the user'"'"'s individual user key and the public pair key stored by one of the users, wherein a subset of trustees containing less than a given number of trustees does not possess any useful information for reconstructing the private pair key; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (6, 10, 11, 12, 13, 14)
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15. A method for enabling two users of a cryptosystem to generate and use a private pair key to encipher communications between the two users, comprising the steps of:
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for each user and each trustee of a group of trustees, having at least one individual user key; having at least one of the two users receive at least a public pair key for the two users, wherein at least one public pair key is computed by an entity that cannot compute all individual user keys; having at least one of the two users use a physical device to compute the private pair key from information that includes the user'"'"'s individual user key and at least one public pair key, wherein a subset of trustees containing less than a given number of trustees does not possess any useful information for reconstructing the private pair key; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (16, 17)
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18. A method for enabling two users of a cryptosystem to generate and use a private pair key to encipher communications between the two users, comprising the steps of:
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for each user and each trustee of a group of trustees, having at least one individual user key; having at least one of the two users receive at least a public pair key for the two users; having at least one of two users use a physical device to compute the private pair key from information that includes the user'"'"'s individual user key and the public pair key received by one of the users, wherein a subset of trustees containing less than a given number of trustees does not possess any useful information for reconstructing the private pair key, and wherein a subset of trustees containing more than a given number of trustees can reconstruct individual user keys of a given user for the purpose of enabling monitoring of communications relative to that user while preserving privacy of the communications of other users; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (19, 20)
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21. A method for enabling two users of a cryptosystem to generate and use a private pair key to encipher communications between the two users, comprising the steps of:
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for each user and each trustee of a group of trustees, having at least one individual key; having at least one of the two users receive from a trustee information for the two users from which the user derives and stores, in a physical device, key information; having at least one of two users use the physical device to compute the private pair key from information that includes the user'"'"'s individual user key and the stored key information, wherein a subset of trustees containing less that a given number of trustees does not possess any useful information for reconstructing the private key; a subset of trustees containing less than a given number of trustees does not possess any useful information for reconstructing the private pair key; having one of the users generate a ciphertext using the private pair key; and transmitting the ciphertext from the user to other user of the cryptosystem. - View Dependent Claims (22, 23, 24)
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25. The method as described in claim 29 wherein the entity is prevented from computing individual keys because such individual keys are stored in physically-secure devices.
Specification