Cryptography – Communication system using cryptography – Time segment interchange
Reexamination Certificate
2006-04-17
2009-10-06
Chai, Longbit (Department: 2431)
Cryptography
Communication system using cryptography
Time segment interchange
C713S189000, C713S190000, C713S191000, C713S192000, C713S193000, C726S027000, C726S028000, C726S029000, C726S030000
Reexamination Certificate
active
07599492
ABSTRACT:
A system, method and computer program product for recovering a key used to produce a ciphertext document from a plaintext document, including, in the ciphertext document encrypted using an N-bit key, identifying location of an M-bit control value; converting the control value to an M-bit portion of a gamma that corresponds to (a) the ciphertext document and (b) the N-bit key; accessing a file that corresponds to the M-bit portion of the gamma, wherein the file includes approximately 2N-Mkeys that correspond to the M-bit portion of the gamma out of the 2Nkeys; testing the 2N-Mkeys using a cryptographic key validity function, until a valid key is found; and decrypting the ciphertext document using the valid key to produce the plaintext document. The keys in the file can be tested sequentially. The file can be requested from a server prior to accessing it, or can be local. The name of the file can include the M-bit portion of the gamma. The ciphertext document can be encrypted, for example, using a symmetric stream cipher. In one example, N=40 and M=16. More generally, usually M<N.
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patent: 2002/0159598 (2002-10-01), Rubinstein et al.
patent: 2003/0115477 (2003-06-01), Baldwin et al.
Phillipe (“Making a Faster Cryptanalytic Time-memory Trade-Off”, 2003).
Philip Oechslin, Making a Faster Cryptanalytic Time-Memory Trade-Off, 2003.
Clark, Beginning To See The Light, http://www.beginningtoseethelight.org
tsecurity/index.php, Apr. 2005.
Golubev Ivan V.
Katalov Vladimir Y.
Malyshev Andrey E.
Sklyarov Dmitry V.
Bardmesser Law Group
Chai Longbit
Elcomsoft Co. Ltd.
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