Debian Bug report logs - #661152
puttygen 2048 bit rsa keys have 2047 bit fingerprints

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: "Karl O. Pinc" <kop@meme.com>

To: Debian Bug Tracking System <submit@bugs.debian.org>

Subject: puttygen 2048 bit rsa keys have 2047 bit fingerprints

Date: Fri, 24 Feb 2012 09:34:31 -0600

Package: putty
Version: 0.60+2010-02-20-1
Severity: normal
Tags: upstream

Hi,

When making 2048 bit rsa keys with puttygen about half the time
puttygen reports the key to be 2047 bits in the fingerprint.

I tried this with the putty snapshot putty-0.62-2012-02-24.tar.gz
as well (from 
http://tartarus.org/~simon/putty-snapshots/putty.tar.gz
)

To reproduce do something like:

 for i in 1 2 3 4 5 6 7 8 9 10 ; do
   ../putty-0.62-2012-02-24/puttygen -o foo$i.ppk -C 'some comment' \
                                     -t rsa -b 2048 
   ../putty-0.62-2012-02-24/puttygen foo$i.ppk -l
 done


-- System Information:
Debian Release: 6.0.4
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: i386 (i686)

Kernel: Linux 2.6.32-5-686 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages putty depends on:
ii  libatk1.0-0           1.30.0-1           The ATK accessibility toolkit
ii  libc6                 2.11.3-2           Embedded GNU C Library: Shared lib
ii  libcairo2             1.8.10-6           The Cairo 2D vector graphics libra
ii  libfontconfig1        2.8.0-2.1          generic font configuration library
ii  libfreetype6          2.4.2-2.1+squeeze3 FreeType 2 font engine, shared lib
ii  libglib2.0-0          2.24.2-1           The GLib library of C routines
ii  libgtk2.0-0           2.20.1-2           The GTK+ graphical user interface 
ii  libpango1.0-0         1.28.3-1+squeeze2  Layout and rendering of internatio
ii  libx11-6              2:1.3.3-4          X11 client-side library
ii  putty-tools           0.60+2010-02-20-1  command-line tools for SSH, SCP, a

putty recommends no packages.

Versions of packages putty suggests:
pn  putty-doc                     <none>     (no description available)

-- no debconf information

Message #10 received at 661152@bugs.debian.org (full text, mbox, reply):

From: "Karl O. Pinc" <kop@meme.com>

To: 661152@bugs.debian.org

Subject: IT seems the key itself is 2047 bits

Date: Fri, 24 Feb 2012 09:41:42 -0600

Hi,

Looking at the keys with openssl (after
converting to openssh-private with puttygen)
it seems some of the keys themselves are 2047 bits.

for f in $(ls) ; do 
  puttygen $f -O private-openssh -o /dev/stdout \
    | openssl rsa -text
done


Karl <kop@meme.com>
Free Software:  "You don't pay back, you pay forward."
                 -- Robert A. Heinlein

Message #15 received at 661152@bugs.debian.org (full text, mbox, reply):

From: Colin Watson <cjwatson@debian.org>

To: "Karl O. Pinc" <kop@meme.com>, 661152@bugs.debian.org

Subject: Re: Bug#661152: puttygen 2048 bit rsa keys have 2047 bit fingerprints

Date: Sun, 4 Mar 2012 16:01:29 +0000

On Fri, Feb 24, 2012 at 09:34:31AM -0600, Karl O. Pinc wrote:
> When making 2048 bit rsa keys with puttygen about half the time
> puttygen reports the key to be 2047 bits in the fingerprint.

  http://the.earth.li/~sgtatham/putty/0.62/htmldoc/Chapter8.html#puttygen-strength

"Note that an RSA key is generated by finding two primes of half the
length requested, and then multiplying them together.  For example, if
you ask PuTTYgen for a 1024-bit RSA key, it will create two 512-bit
primes and multiply them.  The result of this multiplication might be
1024 bits long, or it might be only 1023; so you may not get the exact
length of key you asked for.  This is perfectly normal, and you do not
need to worry.  The lengths should only ever differ by one, and there is
no perceptible drop in security as a result."

That said, since this frequently confuses users, I might backport the
recent upstream change to ensure that some of the top bits are always
set.

-- 
Colin Watson                                       [cjwatson@debian.org]

Message #20 received at 661152-close@bugs.debian.org (full text, mbox, reply):

From: Colin Watson <cjwatson@debian.org>

To: 661152-close@bugs.debian.org

Subject: Bug#661152: fixed in putty 0.62-6

Date: Sun, 04 Mar 2012 17:08:03 +0000

Source: putty
Source-Version: 0.62-6

We believe that the bug you reported is fixed in the latest version of
putty, which is due to be installed in the Debian FTP archive:

pterm_0.62-6_i386.deb
  to main/p/putty/pterm_0.62-6_i386.deb
putty-doc_0.62-6_all.deb
  to main/p/putty/putty-doc_0.62-6_all.deb
putty-tools_0.62-6_i386.deb
  to main/p/putty/putty-tools_0.62-6_i386.deb
putty_0.62-6.debian.tar.gz
  to main/p/putty/putty_0.62-6.debian.tar.gz
putty_0.62-6.dsc
  to main/p/putty/putty_0.62-6.dsc
putty_0.62-6_i386.deb
  to main/p/putty/putty_0.62-6_i386.deb



A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 661152@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Colin Watson <cjwatson@debian.org> (supplier of updated putty package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@debian.org)


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Format: 1.8
Date: Sun, 04 Mar 2012 16:09:28 +0000
Source: putty
Binary: pterm putty putty-tools putty-doc
Architecture: source i386 all
Version: 0.62-6
Distribution: unstable
Urgency: low
Maintainer: Colin Watson <cjwatson@debian.org>
Changed-By: Colin Watson <cjwatson@debian.org>
Description: 
 pterm      - PuTTY terminal emulator
 putty      - Telnet/SSH client for X
 putty-doc  - PuTTY HTML documentation
 putty-tools - command-line tools for SSH, SCP, and SFTP
Closes: 661152
Changes: 
 putty (0.62-6) unstable; urgency=low
 .
   * Backport from upstream (Simon Tatham, Jacob Nevins):
     - Generate keys more carefully, so that when the user asks for an n-bit
       key they always get an n-bit number instead of n-1.  The latter was
       perfectly harmless but kept confusing users (closes: #661152).
Checksums-Sha1: 
 3ec8353697a8ec1d196ac8bdaf3b8174a7ffd988 2017 putty_0.62-6.dsc
 4bb841603f516daa528d2f10ac963167ef6e1d17 15693 putty_0.62-6.debian.tar.gz
 e41df5dbc2e40f485104f52d1379a3cd472bfbd3 197482 pterm_0.62-6_i386.deb
 aab213cc18642beb0eabda45c657fb4a003bd0f4 337346 putty_0.62-6_i386.deb
 f4a4763e659f429efbc1feeda4d116c5a9deaac5 689800 putty-tools_0.62-6_i386.deb
 855f36bcd14aa004ff4876f9b16425b31d98b4c5 173602 putty-doc_0.62-6_all.deb
Checksums-Sha256: 
 237e2cc2cb15d4f51b187ed850cd64720b83ac2bb9a63093bfd29fecd12919e4 2017 putty_0.62-6.dsc
 7e38d0885225a7b395ab1cc16c7624b04da07aecc979b3584ea73defb006e5aa 15693 putty_0.62-6.debian.tar.gz
 9c22af03c61c685ad8c825ebb8bb651e5653d01483e9772b6bf8595d8c67a67a 197482 pterm_0.62-6_i386.deb
 2c5253d243c1f1ba4cf3cc71d4ef33119f6d0887908438ec0b2bc4d8e13aaba3 337346 putty_0.62-6_i386.deb
 3b684f1bb4e0251ae2d8ce2dbb1d6ee3e27244e2dbe22d8e5e414e52a31a0c93 689800 putty-tools_0.62-6_i386.deb
 d8dc723e817cbb667119e2d82561cf11e517d9e825322a4c1f9e738e9309f83e 173602 putty-doc_0.62-6_all.deb
Files: 
 992ed4fd259300ac8306386adbfc1b7a 2017 net optional putty_0.62-6.dsc
 99828b748f55ee635e4077d7105fbce3 15693 net optional putty_0.62-6.debian.tar.gz
 3c4eb95eca221bf2f51da2bc9f551aeb 197482 x11 optional pterm_0.62-6_i386.deb
 69c926449312fc5f942014ad5e9ab30f 337346 net optional putty_0.62-6_i386.deb
 aae0545934709482748f5c4dcaa1dc5b 689800 net optional putty-tools_0.62-6_i386.deb
 b593940e4edce5617a35f0639a400de5 173602 doc optional putty-doc_0.62-6_all.deb

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