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I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except...

In order to allow users to login and maintain compatibility with the existing software installation, we need to figure out what encryption/hashing method the previous vendor was using without access to their source code.

I have a file with an ID and Password column. The password column appears to contains only 16 characters per record, all binary.

Part of the previous vendor system was written in native green screen on the 400, and part of it was written in Microsoft ASP.Net.

What type of encryption or hash would be:

  1. Used by an AS/400 or iSeries Green Screen app, and
  2. Used by a Microsoft .NET app, and
  3. Output a consistent 16 binary bytes, regardless of input length

Pointers much appreciated. Thanks!

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    $\begingroup$ I suppose this is the kind of questions that would better be on Stackoverflow.com $\endgroup$
    – ir01
    Aug 3, 2011 at 20:15
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    $\begingroup$ Let's start narrowing it down. You can create password hashes at will, right? If you hash the same password twice, do you get the same hash? (No, I'm not assuming they did anything right.) If you get the same hash, is it the MD5 of the password? $\endgroup$
    – Gilles 'SO- stop being evil'
    Aug 3, 2011 at 21:19
  • $\begingroup$ I'm closing this question for two reasons: (1) it is a cross-post of this SO question and (2) because it does not appear to be about cryptography within the scope defined in the help center. Somewhat along the lines of Requests for analyzing ciphertext or reviewing full cryptographic designs are off-topic, as the results are rarely useful to anyone else and/or would be too long for this site. $\endgroup$
    – e-sushi
    Jun 30, 2016 at 8:47

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Wikipedia has a list of cryptographic hash functions, together with their output size. 16 bytes are 128 bits. From the list, the following ones could be candidates:

  • MD2, MD4, MD5
  • RIPEMD / RIPEMD-128
  • HAVAL-128

The most probable one would be MD5, so start with this.

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  • $\begingroup$ Thank you for the pointers. I've determined it is not a salt-free MD5, continuing to look at the other options. $\endgroup$
    – gahooa
    Aug 10, 2011 at 19:27

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