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Date: Sun, 22 Mar 2015 23:08:57 -0400 (EDT)
From: "David A. Wheeler" <dwheeler@...eeler.com>
To: "oss-security" <oss-security@...ts.openwall.com>
Subject: Re: CVE for Kali Linux

On Sun, 22 Mar 2015 17:34:29 -0700, Russ Allbery <eagle@...ie.org> wrote:
> Debian signs the entire repository state, not each individual package.
> This has its pluses and minuses....
> Basically, the signing algorithm for a Debian repository rolls up all the
> hashes for each individual package in the archive and signs the whole thing...

Cygwin takes the same approach.  It distributes a file listing packages
(including their names, cryptographic hashes, and lengths), and this file list is signed.
The Cygwin package manager downloads actual packages from untrusted locations,
but before installing it, it checks if the package hash and length match the digitally-signed values
(using a public key embedded in the package manager's executable).

Currently Cygwin uses MD5 as its cryptographic hash algorithm, which has been totally
busted as a crypto hash algorithm. Yes, Cygwin also checks the length,
but I think using MD5 in 2015 is absurd.  Thankfully, the Cygwin folks are
already in the process of moving to SHA-512; once that move completes,
they should be much stronger against MITM attacks.

--- David A. Wheeler

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