Fast cryptographic key recovery system and method
US7599492B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Apr 17, 2006 |
| Grant date | Oct 6, 2009 |
| Priority date | — |
| Expiry date | Jun 13, 2028 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L9/0894
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
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-M keys that correspond to the M-bit portion of the gamma out of the 2N keys; testing the 2N-M keys 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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.