How to Break Password Protected Excel File
What’s the advantage of expensive Excel password recovery applications over their cheaper analogs, and when this advantage doesn’t matter? When you need only a web browser to recover an Excel password? Which tool to use to recover an Excel password? This little summary with useful tips and video examples will provide answers to these questions and help you make a better choice.
Password protection in Excel
Microsoft Excel uses three types of password protection:
- Simple protection, which can be removed instantly
- Strong protection with a secret, which can be removed in several minutes
- Strong protection without any secrets, which is hard to remove
Simple password protection in Excel
In case of simple protection, the password can be removed instantly: Just select the Excel file and retrieve (or remove) the password. Both cheap and expensive applications are equally effective in removing simple protection in all Excel versions.
Simple protection is used in Excel in the following cases:
- Password to Modify
- Workbook password
- Sheet protection
- Excel VBA password
- Password to open for Excel 6–95
If you’ve forgotten an Excel password, even the cheapest app will instantly remove such protection. You will not see any difference.
Strong protection with a secret in Excel
Strong protection in Excel is a Password to Open a document.
Starting from Microsoft Excel 97, such a password cannot be recovered instantly. Instead, you have to use the brute-force approach (that is, to check all possible passwords).
But in case of Excel 97–2003, there is a secret...
These Excel versions use a 40-bit encryption key for strong password protection. Such a short key can be brute-forced fairly quickly. When you get that key, you can easily decrypt the document — and extract all the data contained! You don’t even need to obtain the password!
Expensive applications can recover the encryption key.
Very expensive applications and online services use so-called “rainbow tables” for that purpose and can reliably decrypt any password-protected Excel 97–2003 file in minutes!
Strong protection without a secret in Excel
There are no secrets that let you easily open a password-protected Excel 2007–2013 file.
Instead, you have to painstakingly recover the password by checking all possible passwords one by one, until you find the real one.
And there are other obstacles too!
Password-to-open checking in Excel is artificially slowed down to make it harder to brute-force passwords. For example, password checking in Excel 2010 is about twice as slow as that in Excel 2007.
The above factors define the requirements to applications for Microsoft Excel 2007–2013 password recovery:
- Flexible tuning of the range of values to be checked
- Maximum password-checking speed
Expensive applications provide all you need to fine-tune a password search (position masking for password generation, combination and mutation of passwords from dictionaries, etc.) and can use AMD/NVIDIA video cards to speed-up the search by tens of times (so-called “GPU acceleration”).
Expensive applications are faster and more universal, but that doesn’t matter if you only need to remove simple protection (applies to all Microsoft Excel versions). A web browser and an online service with rainbow tables will let you easily remove any Excel 97–2003 password-to-open. In other cases, you will need a password-recovery application that can use AMD/NVIDIA video cards (GPU acceleration).