An improved ppt2003 file deciphering method and device

A file and header file technology, applied in the field of information security, can solve problems such as password error, inability to decrypt each object, inability to open encrypted files correctly, etc., to ensure correctness, speed up cracking, and reduce the amount of calculation.

Active Publication Date: 2021-01-19
GUANGZHOU HUIRUI SITONG INFORMATION SCI & TECH CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, when PPT2003 files are encrypted, the encryption key consists of 16 bytes, the first 5 bytes are consistent with the first 5 bytes of the initial key, and the last 11 bytes are all 0 by default, that is, only the first 5 bytes are valid. In this way, there is a problem in attacking according to the above method. If the first 5 bytes of the initial key generated by the two passwords are consistent, the two passwords can be verified, but each object in the PPT2003 file uses the block number plus the initial key. Further generate the key used for its own encryption, so if the initial key generated by the password to be verified is not equal to the initial key generated by the correct password, even if the above verification can be passed, each object in the file cannot be decrypted, that is, it cannot Open encrypted files correctly
[0005] Therefore, there are loopholes in the above method, and the deciphered password may be wrong

Method used

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  • An improved ppt2003 file deciphering method and device
  • An improved ppt2003 file deciphering method and device

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Embodiment 1

[0032] as attached figure 1 As shown, this embodiment discloses a process of an improved PPT2003 file deciphering method, which deciphering method includes:

[0033] S1, deciphering parameter analysis step, from the encrypted file to be deciphered, extract the parameters and ciphertext required for deciphering, wherein, the parameters required for deciphering include salt value, encrypted fresh number and its corresponding hash value, encrypted documentAtom header file data;

[0034] S2. The initial encryption key calculation step is to calculate the initial encryption key key according to the input password password and salt value;

[0035] S3, the symmetric encryption algorithm key calculation step, according to the initial encryption key key, select the block number corresponding to the documentAtom header file data, and generate the symmetric encryption algorithm key key1 required for decrypting the documentAtom header file data according to the hash algorithm;

[0036] ...

Embodiment 2

[0041] In this embodiment, the file header of documentAtom is used as fixed data, and the corresponding block number is 2. Assume that the newly added password verification of the present invention is the first password verification, and the original password verification is the second password verification. The specific deciphering method is as follows:

[0042] R1. Obtain the salt value, the encrypted fresh number and its corresponding hash value, and the encrypted documentAtom header file data from the encrypted PPT2003 file.

[0043] R2, according to the input password password and salt value, and then use the hash algorithm to generate the key key required for decryption.

[0044] R3. Using the key key and the block number 2 corresponding to the documentAtom, generate the key key1 required for decrypting the documentAtom header file.

[0045] R4. Use the key key1 to decrypt the encrypted documentAtom header file data, and then compare them. If they are not equal, it is ...

Embodiment 3

[0051] as attached figure 2 As shown, an improved PPT2003 file deciphering device, the deciphering device includes deciphering parameter analysis unit, initial encryption key calculation unit, symmetric encryption algorithm key calculation unit, decryption unit, first password verification unit connected in sequence and the second password verification unit, wherein,

[0052] The deciphering parameter parsing unit is used to extract the parameters and ciphertext required for deciphering from the encrypted file to be deciphered, wherein the parameters required for deciphering include salt value, encrypted fresh number and its corresponding hash value, Encrypted documentAtom header file data;

[0053] The initial encryption key calculation unit is used to calculate the initial encryption key key according to the input password password and salt value;

[0054] The symmetric encryption algorithm key calculation unit is used to select the block number corresponding to the docum...

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Abstract

The invention discloses an improved PPT2003 file decoding method and device. The method comprises the steps: S1, the decoding parameter analysis step: the parameters and the ciphertext required for decoding are extracted from the encrypted file to be decoded; S2, the initial encryption key calculation step: the initial encryption key is calculated; S3, the symmetric encryption algorithm key calculation step: the required symmetric encryption algorithm key1 is decrypted; S4, the decryption step: the encrypted documentAtom header file data are decrypted by using the symmetric encryption algorithm key1; S5, the first time of password verification step: the encrypted fixed data are decrypted by using the symmetric encryption algorithm key1 and compared with the known fixed data so as to determine whether the password to be verified is the possibly correct password; and S6, the second time of password verification step: the second time of verification is performed on the password passing the first time of password verification so as to determine whether the password is the correct password.

Description

technical field [0001] The invention relates to the technical field of information security, in particular to an improved PPT2003 file deciphering method and device. Background technique [0002] PPT2003 files are compound files, and a compound document (Compound Document) is a document that includes not only text but also graphics, spreadsheet data, sound, video images, and other information. Think of a compound document as an owner that holds text, graphics, and multimedia information such as sound and images. The current trend in creating compound documents is to use object-oriented techniques, where non-standard information such as images and sounds can be included in the document as independent, self-contained objects. Microsoft Windows uses this technology, called "OLE2storage file format" or "Microsoft Office compatible storage file format". [0003] PPT2003 file protection is now mainly based on password protection. An encryption key is generated according to the p...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H04L29/06H04L9/32
CPCH04L9/3226H04L9/3234H04L9/3236H04L63/0435H04L63/083
Inventor 黄晓光
Owner GUANGZHOU HUIRUI SITONG INFORMATION SCI & TECH CO LTD
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