crypto-slides-20-secret-sharing.1x1

crypto-slides-20-secret-sharing.1x1 - Secret Sharing See:...

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Unformatted text preview: Secret Sharing See: Shamir, How to Share a Secret , CACM, Vol. 22, No. 11, November 1979, pp. 612–613 c circlecopyrt Eli Biham - August 18, 2010 584 Secret Sharing (20) How to Keep a Secret Key Securely Information can be secured by encryption under a secret key. The ciphertext can be replicated. Even if one replicated copy is lost, or stolen, the information remains available and secure. Therefore, the problem of securing information reduces to the problem of se- curing the secret key. • Encrypting the key does not help - need to secure another key • Replicating the key itself is insecure Goal : Distribute the key to a group, without revealing the key to any subgroups c circlecopyrt Eli Biham - August 18, 2010 585 Secret Sharing (20) Application • An employee looses a key ⇒ The company looses the encrypted informa- tion • In particular: Quits his job, dies • If a copy of the key (or information) is given to others to protect against lost, they can use the key (or information) • In general, we need a way to share a secret in a group, without revealing the secret to any party (or small subgroup), and without allowing any party to inhibit reconstruction c circlecopyrt Eli Biham - August 18, 2010 586 Secret Sharing (20) • Secret Sharing Definition : Secret Sharing schemes ( ñóúù ) • Sharing a secret between n parties • Each party receives a share • Cooperation of predefined subgroups enables to reconstruct the secret • Smaller subgroups cannot reconstruct the secret, nor any information on the secret c circlecopyrt Eli Biham - August 18, 2010 587 Secret Sharing (20) ( k,n )-Threshold Schemes Definition : ( k,n )-Threshold Schemes ((k,n) óñúîëñ ) satisfy • Sharing a secret between n parties • Each party receives a share • Cooperation of any k parties enables to reconstruct the secret • Single parties, or subgroups of up to k − 1 parties, cannot reconstruct the secret, nor any information on the secret c circlecopyrt Eli Biham - August 18, 2010 588 Secret Sharing (20) Example Let S be a 56-bit DES key.be a 56-bit DES key....
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This note was uploaded on 04/14/2011 for the course CS 236506 taught by Professor Yanivcarmeli during the Spring '11 term at Technion.

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crypto-slides-20-secret-sharing.1x1 - Secret Sharing See:...

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