Fast cryptographic key recovery system and method

A system for recovering a key used to produce a ciphertext document from a plaintext document, the system comprising:

• a plurality of 2M files, each file containing to a subset of approximately 2N-M keys out of a total of 2N keys, wherein the keys in each file correspond to an M-bit portion of a gamma;
• means for identifying, in the ciphertext document encrypted using an N-bit key, location of an M-bit control value;
• means for converting the control value to the M-bit portion of the gamma that uniquely corresponds to (a) the ciphertext document and (b) the N-bit key;
• means for accessing a file, out of the plurality of M files, that corresponds to the M-bit portion of the gamma of the cipher text document which serves as an index to select the file, wherein the file includes approximately 2N-M keys that correspond to the M-bit portion of the gamma out of the 2N keys;
• means for testing the 2N-M keys in the file using a cryptographic key validity function until a valid key is found and recovered;
• and
• means for decrypting the ciphertext document using the valid recovered key to produce the plaintext document.

A computer program product for recovering a key used to produce a ciphertext document from a plaintext document, the computer program product embedded on a computer readable storage medium having computer program logic stored thereon for executing on a processor, the computer program logic comprising:

• computer program code means for identifying location of an M-bit control value in the ciphertext document encrypted using an N-bit key;
• computer program code means for converting the control value to an M-bit portion of a gamma that uniquely corresponds to (a) the ciphertext document and (b) the N-bit key;
• computer program code means for accessing a file that corresponds to the M-bit portion of the gamma of the cipher text document which serves as an index to select the file, wherein the file includes approximately 2N-M keys that correspond to the M-bit portion of the gamma out of the 2N keys;
• computer program code means for testing the 2N-M keys using a cryptographic key validity function, until a valid key is found and recovered;
• and
• computer program code means for decrypting the ciphertext document using the valid recovered key to produce the plaintext document.

A system for recovering a key used to produce a ciphertext document from a plaintext document, the system comprising:

• generating a plurality of 2M files, each file containing to a subset of approximately 2N-M keys out of a total of 2N keys, wherein the keys in each file correspond to an M-bit portion of a gamma;
• means for identifying, in the ciphertext document encrypted using an N-bit key, location of an M-bit control value;
• means for converting a control value to the M-bit portion of the gamma that uniquely corresponds to (a) the ciphertext document and (b) the N-bit key;
• means for identifying a file, out of the plurality of M files, that corresponds to the M-bit portion of the gamma of the ciphertext document which serves as an index to select the file;
• means for accessing the file, wherein the file includes approximately 2N-M keys that correspond to the M-bit portion of the gamma out of the 2N keys;
• means for testing the 2N-M keys in the file using a cryptographic key validity function until a valid key is found and recovered;
• and
• means for providing, to a user, one of (a) the valid recovered key, and (b) a plaintext document from the ciphertext document decrypted with the valid recovered key.