Method for generating/regenerating an encryption key for a cryptographic method

• US 7,162,037 B1
• Filed: 07/06/2000
• Issued: 01/09/2007
• Est. Priority Date: 07/27/1999
• Status: Expired due to Term

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Schwenk, Joerg
• Primary Examiner(s): Zand; Kambiz
• Assistant Examiner(s): Ho; Thomas
• Application Number:
  US10/049,258
• Time in Patent Office: 2,378 Days
• Field of Search: 380/44, 380/286, 380/278, 380/279, 380/262, 713/171
• US Class Current: 380/286
• CPC Class Codes: H04L 9/0841 involving Diffie-Hellman or related key agreement protocols
• CPC Class Codes: H04L 9/0869 involving random numbers or seeds

Abstract

A method for generating/regenerating an encryption key for a cryptographic method including the encryption key as well as a public key being generated using a predefined deterministic method from a large random number (seed), where the seed is only generated on the user side, and for which quantities available only to the user are consulted. Regeneration information (R), which is suitable for regenerating the seed and from which the seed is able to be derived deterministically by the trust center by linking only to information known to it, may be generated on the user side and stored so as to be secured against lost. In the event of loss of the encryption key, the seed may be reconstructed by the trust center by linking the regeneration information to the secret information.

Claims

1. A method for at least one of generating and regenerating an encryption key for a cryptographic method, comprising:

generating a seed S, the seed S being a large random number, only on a side of a user by consulting at least one quantity u known only to the user, the encryption key C and a public key U being generated from the seed S by using at least one predefined deterministic method;

generating a regeneration information R on the side of the user to regenerate the seed S and from which the seed S may be derived deterministically by a trust center by linking only to a secret information v known to the trust center;

storing the regeneration information R so that the regeneration information R is secured against loss,

wherein if the encryption key C is unavailable then the seed S is reconstructable by the trust center by linking the regeneration information to the secret information v.

2. The method of claim 1, further comprising providing a key agreement mapping k():

k(a value x, a value y)=a value z, and wherein;

a) k(k(u,v),w)=k(k(u,w),v) for all u,v,w;

b) from the knowledge of u and k(u,v), v cannot be inferred;

c) from the knowledge of u, k(u,v) and k(u,w), k(k(u,w),v) cannot be inferred;

wherein a public parameter g known to the trust center and a secret key v available at the trust center are linked to a public key V where V equals k(g,v), of the trust center;

wherein the public key V and the at least one quantity u selected on the user side are linked on the user side to the seed S, where S equals k(V,u);

wherein a key pair made up of an encryption key C and a public user key U is derived from seed S on the user side using the at least one predefined deterministic method; and

wherein to reconstruct the key pair of the encryption key C and the public user key U, the regeneration information R, where R equals k(g,u), is generated on the user side and is stored so as to be protected against loss.

3. The method of claim 1, further comprising providing a key agreement mapping k which is a discrete exponential function modulo a large prime number p:

k(x,y);

=x^y modulo p, and providing that a public parameter g is an element of a mathematical field GF(p) of a high multiplicative power.

4. The method of claim 1, further comprising providing a key agreement mapping k which is a multiplication on an elliptic curve.

5. The method of claim 1, wherein the trust center calculates the seed S, where S equals (R,v), from the regeneration information R so as to reconstruct the encryption key C.

6. The method of claim 1, further comprising deriving a new public key U and a new encryption key C when the seed S is calculated, due to loss of at least one of the encryption key C and the public key U;

and

verifying by the trust center whether the new public key U is identical to the prior public key U,

wherein when verified that the new public key U is identical to the prior public key U then providing a reconstructed encryption key C to the user.

7. The method of claim 2, further comprising providing a plurality of trust centers which employ the key agreement mapping k and the public parameter g;

selecting at least one of the plurality of trust centers, so that each of the selected trust centers assist in generating a partial seed Sv of the seed S being generated on the side of the user and the partial seed Sv being linked on the side of the user to the seed S, in generating the encryption key C;

calculating by the selected trust centers their respective partial seed Sv of the seed S using the regeneration information R, to regenerate the encryption key C in the case of loss;

reconstructing the encryption key C by linking in combination with each other the respective reconstructed partial seed Sv of each respective selected trust center.

8. The method of claim 7, wherein the trust center and the plurality of trust centers each use at least one of a respective different function kv and a respective different public parameter gv to create a separate regeneration information Rv for each of the trust centers selected.