Method and system for protection of digital information

• US 6,038,316 A
• Filed: 09/24/1997
• Issued: 03/14/2000
• Est. Priority Date: 08/21/1995
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Dwork, Cynthia, Halpern, Joseph Y., Lotspiech, Jeffrey Bruce
• Primary Examiner(s): Hayes, Gail O.
• Assistant Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US08/936,207
• Time in Patent Office: 902 Days
• Field of Search: 380/23, 380/25, 380/44, 380/49
• US Class Current: 705/51
• CPC Class Codes: G06F 21/10 Protecting distributed programs or content, e.g. vending or licensing of copyrighted material protection in video systems or pay television H04N7/16 ; Digital rights management [DRM]
• CPC Class Codes: G06F 2211/007 Encryption, En-/decode, En-/decipher, En-/decypher, Scramble, (De-)compress
• CPC Class Codes: G11B 20/00086 Circuits for prevention of unauthorised reproduction or copying, e.g. piracy indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
• CPC Class Codes: G11B 20/00137 involving measures which result in a restriction to contents recorded on or reproduced from a record carrier to authorised users
• CPC Class Codes: G11B 20/00144 involving a user identifier, e.g. a unique customer ID
• CPC Class Codes: G11B 20/00188 involving measures which result in a restriction to authorised devices recording or reproducing contents to/from a record carrier
• CPC Class Codes: G11B 20/00195 using a device identifier associated with the player or recorder, e.g. serial numbers of playback apparatuses or MAC addresses
• CPC Class Codes: G11B 20/0021 involving encryption or decryption of contents recorded on or reproduced from a record carrier
• CPC Class Codes: G11B 20/0071 involving a purchase action
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 9/302 involving the integer factorization problem, e.g. RSA or quadratic sieve [QS] schemes

Abstract

An information processing system including an encryption processing logic module and a decryption processing logic module for enabling the encryption of digital information to be decrypted with a decryption key K. The encryption processing module includes logic for encrypting the digital information, distributing the digital information and authorizing a user to decrypt the information. The decryption processing module includes logic for the user to communicate a user number n_i to receive an authorization number a_i from the authorization logic in the encryption processing module and extrication logic for extricating the decryption key. The user number n_i uniquely identifies, and is valuable to, the user, so valuable in fact that the user would be unwilling to publically dislcose it. The extrication logic operates on a digital signet pair (a_i, n_i) consisting of the authorization number and user number, to extract K. The decryption logic then uses K to make the content available to the user. The extrication function is fully available to the user as a publicly-computable function in which it is computationally infeasible to use the extrication function to determine other valid digital signet pairs which can be used to extract K.

Claims

1. A method for operating a digital information processing system that distributes encryption information from an authorization processor to a plurality of user processors, the method comprising processor executed steps of:

at the authorization processor;

selecting a resilience threshold t, and a number N;

selecting a generator g of a multiplicative subgroup R of Z_N^*, wherein Z_N^* is a set of numbers less than and relatively prime to N and R consists of powers of g mod N;

selecting random numbers k and b₁, . . . , b_t in the range [2;

|R|], where |R| denotes the size of R and where the random numbers are relatively prime to |R|;

generating g_j =g^b.sbsp.j mod N for 1≦

j≦

t;

distributing to the user processors encrypted information with g_j ; and

receiving a value n from a user processor, and returning to the user processor a signet a, wherein;

space="preserve" listing-type="equation">a=k-b.sub.1 n- . . . -b.sub.t n.sup.t mod |R|;

whereby the signet a is for enabling the user processor to generate a decryption key K to decrypt the encrypted information.

2. The method of claim 1, also including:

at the user processor;

receiving the encrypted information with g_i ;

sending n to the authorization processor;

receiving the signet a;

generating K using;

space="preserve" listing-type="equation">K=g.sup.a g.sub.1.sup.n . . . g.sub.t.sup.n.spsp.t mod N;

and, decrypting the encrypted information using K.

3. A method for operating a digital information processing system that distributes encryption information from an authorization processor to a plurality of user processors, the method comprising processor executed steps of:

at the authorization processor;

selecting a resilience threshold t, a security parameter s, and a number N;

selecting a generator g of a multiplicative subgroup R of Z_N^*, wherein Z_N^* is a set of numbers less than and relatively prime to N, and R consists of powers of g mod N;

selecting random numbers k and b₁, . . . , b_2t in the range [2;

|R|], where |R| denotes the size of R and where the random numbers are relatively prime to |R|;

generating additional generators g_j, wherein g_j =g^b.sbsp.j, and 1≦

j≦

2t;

distributing to the user processors encrypted information with g₁, . . . g_2t ;

receiving a value n from a user processor;

in response to n;

randomly selecting an ordered list of s indices i₁, . . . , i_s, where 1≦

i_j ≦

m and m=2t; and

returning to the user processor a signet a, wherein;

space="preserve" listing-type="equation">a=(k-b.sub.i.sbsb.1 n-. . . -b.sub.i.sbsb.s n.sup.s) mod |R|, together with the ordered list

whereby, the signet a is for enabling the user processor to generate a decryption key k to decrypt the encrypted information.

4. The method of claim 3, also including:

at the user processor;

receiving the encrypted information with g₁, . . . , g_2t ;

sending n to the authorization processor;

receiving the signet a and the ordered list;

generating K using;

space="preserve" listing-type="equation">K=g.sup.a g.sub.i.sbsb.1.sup.n . . . g.sub.i.sbsb.s.sup.n.spsp.s mod N

and, decrypting the encrypted information using K.

5. A method for operating a digital information processing system that distributes encryption information from an authorization processor to a plurality of user processors, the method comprising processor executed steps of:

at the authorization processor;

selecting a resilience threshold t, a security parameter s, a number N, and a number m, where m=2t and is evenly divisible by s;

selecting a generator g of a multiplicative subgroup of R of Z_N^*, wherein Z_N^* is a set of numbers less than and relatively prime to N, and R consists of the powers of g mod N;

selecting random numbers k and b₁, . . . , b_2t in the range [2;

|R|], where |R| denotes the size of R and where the random numbers are relatively prime to |R|;

generating additional generators g₁, . . . , g_m, where g_i =g^b.sbsp.i and 1≦

i≦

2t;

partitioning the generators g₁, . . . , g_m into m/s pairwise disjoint sets S₁, . . . , S_m/s ;

receiving a value n from a user processor;

in response to n;

randomly selecting an index j in the range [1;

m/s];

using the set S_j containing generators g_j1, . . . , g_js and the random numbers b_j1, . . . , b_js that define those generators, returning to the user processor a signet a, wherein;

space="preserve" listing-type="equation">a=k-b.sub.j1 n- . . . -b.sub.js n.sup.s, together with the index j

whereby the signet a is for enabling the user processor to generate a decryption key K to decrypt the encrypted information.

6. The method of claim 5, also including:

at the user processor;

receiving the encrypted information with g, g₁, . . . , g_m ;

sending n to the authorization processor;

receiving the signet a and the index j;

generating K using;

space="preserve" listing-type="equation">K=g.sup.a g.sub.j1.sup.n . . . g.sub.j1.sup.n mod N;

and, decrypting the encrypted information using K.