[RESOLVED] Avoiding Duplicates in Random Passwords
I need to generate a pattern of random string for each file name in a specific directory.
but i don't know why i have a duplicate result!
Code:
Option Explicit
Private Const C_EKEY As Double = 1.123
Public Function sRandomString(iLength As Integer, ByVal strSeed As String) As String
Dim i As Integer
Dim j As Integer
Dim s As String
Static b As Boolean
Dim lngX As Long
Dim lngI As Long
Dim strMap As String
Dim strPWD As String
For lngX = 1 To Len(strSeed)
lngI = lngI + Asc(Mid$(strSeed, lngX, 1))
Next lngX
Rnd -1
Randomize CInt(lngI * C_EKEY)
Do Until j = iLength
i = Int(100 * Rnd + 36)
s = s + Chr$(i)
j = j + 1
Loop
sRandomString = s
End Function
Re: Avoiding Duplicates in Random Passwords
You're calling Randomize with a non-random seed, so you're guaranteed to get duplicates when you provide the same seed. On top of that, a ton of your "seeds" are equivalent to each other with that weird Asc(Mid$ calculation. VB6's random functions aren't great, but just calling Randomize with no parameters would be vastly better than what you're doing. Or just use FileSystemObject.GetTempName... Are all of the strings you are generating even valid filenames?
Edit: Oh, I got your question backwards. But you don't really want a random string, you want a one-way hash, right? At a minimum you'll want to do a CRC32 on the file name instead of just adding up the ASCII values.
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
ahenry
You're calling Randomize with a non-random seed, so you're guaranteed to get duplicates when you provide the same seed. On top of that, a ton of your "seeds" are equivalent to each other with that weird Asc(Mid$ calculation. VB6's random functions aren't great, but just calling Randomize with no parameters would be vastly better than what you're doing. Or just use FileSystemObject.GetTempName... Are all of the strings you are generating even valid filenames?
Edit: Oh, I got your question backwards. But you don't really want a random string, you want a one-way hash, right? At a minimum you'll want to do a CRC32 on the file name instead of just adding up the ASCII values.
Yes exactly i want (somehow) to get hash for each file name but with more possibilities of characters, more than CRC32 or MD, MD2, MD4, MD5 or SHA, and i don't want to use any of these hashes.
All i want is to use the same function above but without duplicates.
Re: Avoiding Duplicates in Random Passwords
Well if you are dead-set on using the function you posted, then take a crc32 of the initial string, convert the crc to a long, and use that for the Randomize value. It won't be secure, or free of duplicates unless your file names are really short, but you won't produce duplicates all the time like the current code does.
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
ahenry
Well if you are dead-set on using the function you posted, then take a crc32 of the initial string, convert the crc to a long, and use that for the Randomize value. It won't be secure, or free of duplicates unless your file names are really short, but you won't produce duplicates all the time like the current code does.
I'll try that, Thank you ahenry.
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
BD48
Yes exactly i want (somehow) to get hash for each file name
but with more possibilities of characters...
In case you mean the hex-representation of the binary Hash-Results is too long for you -
you can always switch from Base16 (Hex, having 16Chars in the alphabet) to another alphabet with "more chars" (e.g. Base64).
But you will still have to hash first.
Here's a little function, how you could reduce the amount of chars from an MD5-Hash, by using Base64-encoding of the resulting Hash-Bytes:
Code:
Function GetBase64Hash(S As String, Optional ByVal CaseSensitive As Boolean) As String
Dim B() As Byte
With New_c.Crypt ' vbRichClient5-cCrypt is used here, but any crypto-class usually offers the two methods below
B = .MD5(IIf(CaseSensitive, S, LCase(S)), False)
'ReDim Preserve B(0 To 8) 'that way one could reduce the 128Bit-Hash to 72Bit
GetBase64Hash = Replace(.Base64Enc(B), "/", "#")
End With
End Function
the above will print for:
Debug.Print GetBase64Hash("MyFile.txt")
a Base64 result-string of:
djdqbHiM+V8x#uwk9R7igQ
and in case you want a shorter String back, you could activate the Redim Preserve line in the above code
(which will increase the collision-probability of the MD5-HashValue - but those 72Bit are still better than a Crc32 or Crc64 value).
The result for the above input ("MyFile.txt") would then come out shortened as:
djdqbHiM+V8x
Olaf
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
Schmidt
In case you mean the hex-representation of the binary Hash-Results is too long for you -
you can always switch from Base16 (Hex, having 16Chars in the alphabet) to another alphabet with "more chars" (e.g. Base64).
But you will still have to hash first.
Here's a little function, how you could reduce the amount of chars from an MD5-Hash, by using Base64-encoding of the resulting Hash-Bytes:
Code:
Function GetBase64Hash(S As String, Optional ByVal CaseSensitive As Boolean) As String
Dim B() As Byte
With New_c.Crypt ' vbRichClient5-cCrypt is used here, but any crypto-class usually offers the two methods below
B = .MD5(IIf(CaseSensitive, S, LCase(S)), False)
'ReDim Preserve B(0 To 8) 'that way one could reduce the 128Bit-Hash to 72Bit
GetBase64Hash = Replace(.Base64Enc(B), "/", "#")
End With
End Function
the above will print for:
Debug.Print GetBase64Hash("MyFile.txt")
a Base64 result-string of:
djdqbHiM+V8x#uwk9R7igQ
and in case you want a shorter String back, you could activate the Redim Preserve line in the above code
(which will increase the collision-probability of the MD5-HashValue - but those 72Bit are still better than a Crc32 or Crc64 value).
The result for the above input ("MyFile.txt") would then come out shortened as:
djdqbHiM+V8x
Olaf
Thank Schmidt, that was a very good idea but i want the result to have more characters like this:
e=g9¿c\.4&)G>?}'NF\c\[¿V7u,woW&#_
sY1%!^5mFu(X,A4%16;98mk#7O:1v:SMJ
my code do that but with duplicates...
Thank You Schmidt for help
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
BD48
Thank Schmidt, that was a very good idea but i want the result to have more characters like this:
e=g9¿c\.4&)G>?}'NF\c\[¿V7u,woW&#_
sY1%!^5mFu(X,A4%16;98mk#7O:1v:SMJ
my code do that but with duplicates...
Thank You Schmidt for help
Out of interest... Why? Is there a reason something like a SHA256 wouldn't be good enough? Do you want this random filename to be truly random or somehow derived from the filename? If derived from the filename why wouldn't a hash be good enough? If it really is a completely random name then would a GUID be any use? Also you example filename contains characters that are illegal in file names so you might want to filter out the reserved characters mentioned here
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
PlausiblyDamp
Out of interest... Why? Is there a reason something like a SHA256 wouldn't be good enough? Do you want this random filename to be truly random or somehow derived from the filename? If derived from the filename why wouldn't a hash be good enough? If it really is a completely random name then would a GUID be any use? Also you example filename contains characters that are illegal in file names so you might want to filter out the reserved characters mentioned
here
PlausiblyDamp, i want to generate a string with combination of every possible characters depending on the file name like you said (derived from the file name), the SHA hash (E1744A525099D9A53C0460EF9CB7AB0E4C4FC939) generate a limited characters and GUID do the same.
but maybe converting the SHA hash to string could help!.
Thank you PlausiblyDamp for help
Re: Avoiding Duplicates in Random Passwords
Quote:
Originally Posted by
BD48
...but maybe converting the SHA hash to string could help!.
Sure ... since any Hash-Function will return a sequence of bytes (as a ByteArray):
- Crc32 = 4Bytes
- MD5 = 16Bytes
- SHA1 = 20Bytes
- SHA256 = 32Bytes
- SHA512 = 64Bytes
...one can then of course use e.g.
StrConv(ByteArray(), vbUnicode, 1033)
to convert those HashByte-Sequences to a String-representation directly (any 8Bit-Value of the ByteArray represented by a Single-Char-Mapping, according to the used CodePage,
which differs from locale to locale though - but could be forced to a specific one, as done above with the magenta-colored "en-US" LCID 1033.
But that introduces problems with "readability" (e.g. when the ByteArray contained Zeroes or Tabs, Linefeeds or other Chars after the CodePage-mapping).
And not only is it readability which suffers - it could also affect "transportability" and your ability to use such a string in a serializing-scenario directly.
That's why most hashes are given in their Hex-representation (with two Hex-Digits-Per-Byte, where even lowercase-uppercase-switchery is tolerated).
The Base64-encoding I've recommended is a compromise, which is not using "a full ANSI-codepage with mappings in the full byte-range of [0 to 255]",
but it maps to only "64 always readable Chars in the low ASCII-range" (at the cost of increasing the length of the mapped HashByte-String by 33%).
Your "fully mapped 8Bit String-representation" could never be concatenated as a Parameter into a Browser-URL for example -
whereas this is no problem with the Hex-representation (as well as the Base64-representation) of a HashBytes-sequence.
Olaf
Re: Avoiding Duplicates in Random Passwords
Olaf, You Helped me very well.
Thank You
