The Microsoft Excel File Format - OpenOffice.org

4.18 Worksheet/Workbook Protection
4.18.3 Workbook Protection (BIFF5-BIFF8)
Definition: Workbook Protection Block
The Workbook Protection Block in the Workbook Globals Substream determines the protected items in the entire
workbook.
The PROTECT record protects the workbook contents and the WINDOWPROTECT record protects the window
settings. The PASSWORD record contains the hash value of the password used to protect the workbook (➜4.18.4). All
the mentioned records occur always, if the file was written by Excel, but may be omitted.
If a protection password is set in the PASSWORD record, the read/write file protection (➜4.19) will be enabled, which
causes encryption of the file (➜4.19.1) in every case. If this protection is not enabled manually while saving the file, the
built-in password “VelvetSweatshop” is used, not the password set for workbook protection.
Structure of the Workbook Protection Block:
○ WINDOWPROTECT Window settings: 1 = protected (➜5.111)
○ PROTECT Workbook contents: 1 = protected (➜5.82)
○ PASSWORD Hash value of the password; 0 = no password (➜5.76)
○ PROT4REV Shared workbook: 1 = protected
○ PROT4REVPASS Hash value of the shared password; 0 = no password
4.18.4 Password Hash Value
In several records the hash value of a password is stored, used for later verification of an entered password. The length of
the password is restricted to 15 characters.
The following pseudo-code algorithm shows how to create such a hash value from a given byte-string password:
ALGORITHM Get_Password_Hash( password )
1) hash ← 0 ; char_index ← char_count ← character count of password
2) char_index ← char_index - 1
3) char ← character from password with index char_index {0 is leftmost character}
4) hash ← hash XOR char
5) rotate the lower 15 bits of hash left by 1 bit
6) IF char_index > 0 THEN JUMP 2)
7) RETURN hash XOR char_count XOR CE4B H
115