Method for providing cryptographical key pairs

1. A method for generating a second asymmetric cryptographical key pair, wherein a first private key (G 0 ) forms a first asymmetric cryptographical key pair (K 0 ) together with a first public key (O 0 ), wherein the method comprises the following steps:

receiving a user identifier,

calculating a second private key (G 1 ), wherein a random value (z) and the user identifier are used in the calculation,

calculating a second public key (O 1 ) from the second private key using an asymmetric cryptographical key generation method, wherein the second private key and the second public key form the second asymmetric cryptographical key pair (K 1 ),

performing an admissibility check on the second private key using a check condition, wherein the check condition comprises the usability of the second private key for generating the second public key from the second private key using an asymmetric cryptographical key generation method,

calculating the second public key from the second private key if the check condition is satisfied,

calculating the second private key with a new random value and repeating the step of performing an admissibility check if the check condition is not satisfied,

generating a first cipher (C_G 0 — O 1 ) by encrypting the first private key (G 0 ) with the second public key (O 1 ),

storing the first cipher (C_G 0 — O 1 ),

storing the random value in a database.

2. The method as claimed in claim 1 , wherein the step of calculating the second private key comprises the application of a one-way function f to the random value and of a function g, wherein the function g is applied to the user identifier.

3. The method as claimed in claim 2 , wherein the function g is a further one-way function.

4. The method as claimed in claim 3 , wherein the function f and/or the function g is/are a cryptographical hash function.

5. The method as claimed in claim 1 , wherein the asymmetric cryptographical key generation method for calculating the second public key is a method on elliptic curves, wherein the second public key is calculated by multiplying the second private key by a curve point on an elliptic curve.

6. The method as claimed in claim 1 , wherein the asymmetric cryptographical key generation method for calculating the second public key is a method on elliptic curves, wherein the second public key is calculated by multiplying the second private key by a curve point on an elliptic curve, wherein the check condition is the condition that the second private key is greater than 1 and less than the order of the elliptic curve.

7. The method as claimed in claim 6 , wherein the check condition is the condition that the bit length of the random value is greater than or equal to the bit length of the order of the elliptic curve.

8. The method as claimed in claim 6 , wherein the check condition is the condition that the random value is chosen such that the value of the generated second private key is less than the order of the elliptic curve.

9. The method as claimed in claim 1 , wherein the asymmetric cryptographical key generation method for calculating the second public key is an RSA method.

10. The method as claimed in claim 1 , wherein the asymmetric cryptographical key generation method for calculating the second public key is an RSA method, wherein the check condition is the condition that Euler's φ function for the modulus n that is used for the RSA key generation method and the second private key do not have a common denominator.

11. The method as claimed in claim 10 , wherein the check condition is also the condition that the second private key has a value between 2 and the value of the φ function of the modulus n used for the RSA key generation method minus 1.

12. The method as claimed in claim 1 , wherein the method is produced by an applet or a browser plug-in or is an independent application which runs on a computer at a trustworthy station or is an embedded application which runs in a protected hardware module.

13. The method as claimed in claim 1 , wherein the method also comprises:

receiving a third private key (G 2 ), wherein the third private key forms a third asymmetric cryptographical key pair (K 2 ) together with a third public key (O 2 ),

receiving a second cipher (C_G 0 — O 2 ), wherein the second cipher comprises the first private key (G 0 ) following encryption with the third public key (O 2 ),

decrypting the second cipher with the third private key (G 2 ) to obtain a first private key (G 0 ).

14. The method as claimed in claim 13 , wherein receiving the third private key comprises the following steps:

receiving a further user identifier,

receiving a further random value, wherein the further random value is associated with the further user identifier,

calculating the third private key (G 2 ), wherein the further random value and the further user identifier are used in the calculation.

15. The method as claimed in claim 13 , wherein the third private key is received from a tangible portable data storage medium.

16. The method as claimed in claim 13 , also having the step of authentication to the database, wherein the second cipher is received from the database following successful authentication.

17. The method as claimed in claim 1 , also having the step of generation of a fourth asymmetric cryptographical key pair, wherein a fourth private key (G 3 ) forms the fourth asymmetric cryptographical key pair (K 3 ) together with a fourth public key (O 3 ), wherein the method comprises the following steps:

receiving the fourth public key (G 3 ),

generating a fourth cipher (C_G 0 — O 3 ) by encrypting the first private key (G 0 ) with the fourth public key (O 3 ),

storing the fourth cipher.

18. The method as claimed in claim 1 , wherein the method is performed on a tangible portable data storage medium.

19. The method of claim 1 , comprising a tangible computer readable medium having instructions which can be executed by a processor for the purpose of performing the method steps.