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Old 02-03-2010, 12:21 PM   #1 (permalink)
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Default Removing Internal XL passwords

McGimpsey & Associates : Excel : Remove internal XL passwords

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Removing Internal XL passwords
Note: For a discussion of File or VBA Project password protection, see here.

Internal XL passwords are about as useful for security as tissue paper. The reason is that the passwords you enter (i.e., with Tools/Protect/Protect Worksheet or /Protect Workbook) are not used directly in protection. Instead they are hashed (mathematically transformed) into a much less secure code. Effectively, any password of any length is transformed into a string of 12 characters, the first 11 of which have one of only two possible values. The remaining character can have up to 95 possible values, leading to only

2^11 * 95 = 194,560potential passwords. This may seem like a lot, but it only takes a few seconds for a modern computer to try them all. As a comparison, a 4-character password containing just the 26 lower case alphabet characters has 456,976 combinations, and a 3-character password consisting of lower case, upper case and the digits 0-9 will have 238,328 combinations.

Again, it doesn't matter what your original password is, one of those 194K strings will unlock your sheet or workbook.
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Old 02-03-2010, 02:48 PM   #2 (permalink)
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Default Re: Removing Internal XL passwords

Nice, so it is much better to use 7Zip to protect such a files, right?
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