Re: How is .net generating extra bits in MD5?
From: Valery Pryamikov (Valery_at_nospam.harper.no)
Date: 01/26/05
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Date: Wed, 26 Jan 2005 23:54:54 +0100
Thanks Shawn for picking up the thread!
I didn't note that Pete was talking about GetBytes() :-(. Next time I should
be reading original poster's question more carefully before answering it
:-).
Pete, sorry for keeping silence for almost a week - I was not able to check
newsgroup earlier...
-Valery.
http://www.harper.no/valery
""Shawn Farkas [MS]"" <shawnfa@online.microsoft.com> wrote in message
news:dJc8TvyAFHA.2504@cpmsftngxa10.phx.gbl...
> Hi Valery,
>
> PasswordDeriveBytes::CryptDeriveKey() uses the CAPI CryptDeriveKey under
> the cover, however Pete is using PasswordDeriveBytes::GetBytes() which
> actually uses PBKDF1 to do its work.
>
> -Shawn
> http://blogs.msdn.com/shawnfa
> --
> This posting is provided "AS IS" with no warranties, and confers no
> rights.
>
>
> Note:
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> --------------------
>> From: "Valery Pryamikov" <Valery@nospam.harper.no>
>> References: <1106337228.327388.91720@z14g2000cwz.googlegroups.com>
>> Subject: Re: How is .net generating extra bits in MD5?
>> Date: Fri, 21 Jan 2005 23:25:58 +0100
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>>
>> Hi,
>> PasswordDeriveBytes does the same thing as CryptDeriveKey and actually
>> involves 3 hashes:
>>
>> K' = H(password)
>> K = H(K' XOR {0x36}) || H(K' XOR {0x5C})
>> where H is hash algorithm, || - concatenation and K' is intermediate key.
>>
>> -Valery.
>> http://www.harper.no/valery
>>
>> "Pete" <jpeteb@hotmail.com> wrote in message
>> news:1106337228.327388.91720@z14g2000cwz.googlegroups.com...
>> > Hi,
>> >
>> > I have a piece of .net code I am trying to understand. It creates a MD5
>> > hash then requests 256 bits from the hash, where MD5 only generates 128
>> > bits. I've looked at the hash with another non-.net piece of code and
>> > the first 128 bits match up correctly. How is Microsoft creating the
>> > second 128 bits? I cannot seem to figure that out. Here is a code
>> > fragment in C#:
>> >
>> > string passPhrase; // password string
>> > string saltValue; // salt string
>> > string hashAlgorithm; // set to "MD5"
>> > int passwordIterations; // set to 2
>> > int keySize; // set to 256
>> >
>> > byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
>> > byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);
>> >
>> > PasswordDeriveBytes password = new PasswordDeriveBytes(
>> > passPhrase,
>> > saltValueBytes,
>> > hashAlgorithm,
>> > passwordIterations);
>> > byte[] keyBytes = password.GetBytes(keySize / 8);
>> >
>> >
>> > TIA for any help.
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