Hiya, vor kurzem fragte hier mal jemand nach dem Format von MD5 Passwörtern. In beigefügter E-Mail ist das Format erläutert. -- Ingo Luetkebohle / 21st Century Digital Boy dev/consulting Gesellschaft fuer Netzwerkentwicklung und -beratung mbH url: http://www.devconsult.de/ - fon: 0521-1365800 - fax: 0521-1365803 ---------- Forwarded message ---------- Date: Thu, 21 Oct 1999 09:24:28 -0400 From: Randy_Labaza@tivoli.com Reply-To: pam-list@redhat.com To: pam-list@redhat.com Subject: Re: Why is the hashed pw so long? Resent-Date: 21 Oct 1999 13:24:37 -0000 Resent-From: pam-list@redhat.com Resent-cc: recipient list not shown: ; Stephen or anyone, Can you give me a pointer (website, book, etc.) to more of the gory details of the MD5 password hash? Such as the encoding of the result, and exactly how the salt is used in the hash, etc. Your description below is the most detail I have found on this. But, I am looking for a few more specifics. Your help is most appreciated. Regards. Randy Labaza rlabaza@tivoli.com stephen langasek <vorlo-@netexpress.net> wrote: original article:http://www.egroups.com/group/pam-list/?start=1903

On Tue, 14 Sep 1999, gg&ht forever wrote:

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This is really not a PAM question per se - it relates to PAM, though. But feel free to point me to another list. Thanks.

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I'm running RH6.0 using md5 and shadow. My understanding is that when MD5 hashes anything it produces a 128-bit output. 128 bits= 16 bytes. So, how come the hashed pw is 34 characters in /etc/shadow?

The first three characters are the magic string $1$, used to distinguish between md5 and crypt. The next 8 characters are the salt, the 12th character is a delimiter character ('$' again), and the remaining 22 characters are the MD5 hash.

128 / 8 = 16, but this assumes you're using all 8 bits of a character. The MD5 hashes in a password file are stored in a human-readable form by convention. I believe they're encoded in base-64: there's a pool of 64 characters to choose from, which means each character only really encodes 6 bits of data (2^6 == 64). 128 / 6 = 21 1/3, which rounded up gives you the 22 you see in /etc/shadow.

(The salt is encoded in a similar fashion--it's stored as 8 bytes in the file, but it's really only a 48-bit salt, not 64.)

-Steve Langasek postmodern programmer

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