An improved ppt2003 file deciphering method and device

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...

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

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