![]() Klein derives a subset of the input passwords that cover all of the possible hashes.īased on this description of Excel's hashing function, the following code generates the same hash as Excel which you can use to test Klein's function. 32768 is a tiny number of things to try when computing power is applied.Because the hashing algorithm generates such small hashes, 15 bits, the number of possible hashes is 2^15 = 32768 hashes.The Excel hash function maps the large space of possible passwords to the small space of possible hashes.The best description by far I've encountered of how brute forcing the Excel hashing algorithm works is on the page links to, posted by Torben Klein. This (usually) makes it more secure than simply storing the password as a string to compare against. Because of the loss of data, it is impossible to reverse a hash to get the original password, but in the future if someone types in a password it can be hashed and compared against the stored hash. A hash is a one-way algorithm that crunches up the bits, losing some information along the way, but generating a fingerprint of the original data. The Excel worksheet password protection works by converting the input password to a hash and stores it. In other words, how come this generated string of A's and B's can be used as the password to a sheet inside a particular workbook ? My question is: What kind of exploit does it use to work? If ActiveSheet.ProtectContents = False Then This option is sometimes used by servers that only allow unencrypted connections.I found this VBA code to unlock sheets without knowing the password: Sub PasswordBreaker()ĭim i As Integer, j As Integer, k As Integerĭim l As Integer, m As Integer, n As Integerĭim i1 As Integer, i2 As Integer, i3 As Integerĭim i4 As Integer, i5 As Integer, i6 As Integerįor i = 65 To 66: For j = 65 To 66: For k = 65 To 66įor l = 65 To 66: For m = 65 To 66: For i1 = 65 To 66įor i2 = 65 To 66: For i3 = 65 To 66: For i4 = 65 To 66įor i5 = 65 To 66: For i6 = 65 To 66: For n = 32 To 126ĪctiveSheet.Unprotect Chr(i) & Chr(j) & Chr(k) & _Ĭhr(l) & Chr(m) & Chr(i1) & Chr(i2) & Chr(i3) & _ CRAM-MD5: Username and password are encrypted.LOGIN and PLAIN: Username and password are not encrypted, but this is still secure if the connection is encrypted. ![]() If the connection type is unencrypted it will try only CRAM-MD5
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