Patent ID: 8345862
Filing Date: 2013-01-01
Classification: H04L

Abstract:
1. A method of sharing a strong secret F between two parties (A, B) who previously share a weak secret f, said method comprising the initial step of choosing a public exponent e of small size, and further comprising the following steps performed by the parties (A, B): for A: 1. randomly drawing two prime numbers p, q, and calculating a modulus n=p*q; 2. from the modulus n and from the exponent e, building a pair of keys of an asymmetric algorithm, namely a public key K 3. drawing a first random number for use as a salt S, and encrypting the modulus n using a symmetric algorithm by using a key KS derived from the weak secret f and from the salt S; and 4. concatenating the salt S and the resulting encrypted modulus n (C for B: 5. deriving the key KS from the weak secret f, and from the salt S extracted from the message M transmitted by A; 6. decrypting the modulus n as encrypted by A, by means of the symmetric algorithm and by using said key KS; 7. drawing a random number that constitutes the strong secret F; and 8. encrypting the strong secret F by means of the asymmetric algorithm and of the public key K for A: 9. decrypting the strong secret F as transmitted encrypted by B, by means of the asymmetric algorithm, by using the private key K