Mailing List Archive

[Bug 1550] Move from 3DES to AES-256 for private key encryption
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #1 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:52:35 ---
Date: Tue, 20 Jan 2009 20:42:38 -0500
From: Jim Knoble <jmknoble@pobox.com>
To: OpenSSH Devel <openssh-unix-dev@mindrot.org>
Subject: Re: OpenSSH private key encryption: time for AES?
Message-ID: <20090121014237.GD29074@crawfish.ais.com>
Mail-Followup-To: OpenSSH Devel <openssh-unix-dev@mindrot.org>
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
In-Reply-To: <alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>

Circa 2009-01-20 02:30 dixit Damien Miller:

: On Tue, 20 Jan 2009, Jim Knoble wrote:
:
: > [...]how can i encrypt my 4096-bit SSH RSA keypair with
: > something like AES-128, AES-256, or Twofish instead of 3DES and
still
: > use it with OpenSSH? Can ssh-add read (unencrypted) key data from
stdin?

Experimentation has shown that the following will add a key to a
running
ssh-agent (OpenSSH_4.6p1, Ubuntu 7.10):

$ cat id_rsa-unencrypted |ssh-add /dev/stdin
$ ssh-add -l |fgrep /dev/stdin
2048 xx:xx:xx:...:xx:xx:xx /dev/stdin (RSA)
$

However, the following will not remove the key from the agent:

$ cat id_rsa-unencrypted |ssh-add -d /dev/stdin
Bad key file /dev/stdin
$

If both operations worked, then one could use an external
encryption/decryption facility with one's private keys, e.g.:

openssl enc -d -in ~/.ssh/id_rsa -aes-256-cbc |ssh-add /dev/stdin

(although it would take a passphrase to remove a key from ssh-agent).

: If you want to change it then you can do something like [a one-liner
: change to authfile.c]. It probably wouldn't hurt to change - new
: installations will still be able to read old keys

It would be nice for newer OpenSSH to be able to produce private keys
usable by older OpenSSH as well.

Any chance of an option in ssh-keygen to specify the cipher? E.g.:

# Use '-E' with any of: 3des-cbc, aes128-cbc, aes192-cbc,
aes256-cbc
ssh-keygen -t rsa -E aes256-cbc

Alternatively:

# Encrypt with AES-256:
ssh-keygen -t rsa -A

# Encrypt with 3DES:
ssh-keygen -t rsa -3

# Use default encryption:
ssh-keygen -t rsa

Finally:

# Encrypt with AES-256:
ssh-keygen -t rsa

# Encrypt with 3DES ('-O' for "old"):
ssh-keygen -t rsa -O:1

Cheers,
jim

--
jim knoble | jmknoble@pobox.com | http://www.pobox.com/~jmknoble/

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[Bug 1550] Move from 3DES to AES-256 for private key encryption [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #2 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:54:11 ---
Date: Wed, 21 Jan 2009 15:16:31 +1100 (EST)
From: Damien Miller <djm@mindrot.org>
To: Jim Knoble <jmknoble@pobox.com>
Subject: Re: OpenSSH private key encryption: time for AES?
In-Reply-To: <20090121014237.GD29074@crawfish.ais.com>
Message-ID: <alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
<20090121014237.GD29074@crawfish.ais.com>
Cc: OpenSSH Devel <openssh-unix-dev@mindrot.org>

On Tue, 20 Jan 2009, Jim Knoble wrote:

> Circa 2009-01-20 02:30 dixit Damien Miller:
>
> : On Tue, 20 Jan 2009, Jim Knoble wrote:
> :
> : > [...]how can i encrypt my 4096-bit SSH RSA keypair with
> : > something like AES-128, AES-256, or Twofish instead of 3DES and still
> : > use it with OpenSSH? Can ssh-add read (unencrypted) key data from stdin?
>
> Experimentation has shown that the following will add a key to a running
> ssh-agent (OpenSSH_4.6p1, Ubuntu 7.10):
>
> $ cat id_rsa-unencrypted |ssh-add /dev/stdin
> $ ssh-add -l |fgrep /dev/stdin
> 2048 xx:xx:xx:...:xx:xx:xx /dev/stdin (RSA)
> $
>
> However, the following will not remove the key from the agent:
>
> $ cat id_rsa-unencrypted |ssh-add -d /dev/stdin
> Bad key file /dev/stdin
> $

Does that work without the patch? I don't think it would even with
the current cipher because it needs to reread the file IIRC.

> If both operations worked, then one could use an external
> encryption/decryption facility with one's private keys, e.g.:
>
> openssl enc -d -in ~/.ssh/id_rsa -aes-256-cbc |ssh-add /dev/stdin
>
> (although it would take a passphrase to remove a key from ssh-agent).

Wouldn't this just require the former to work? You'd be passing keys
to ssh-agent in unencrypted form always, no?

> : If you want to change it then you can do something like [a one-liner
> : change to authfile.c]. It probably wouldn't hurt to change - new
> : installations will still be able to read old keys
>
> It would be nice for newer OpenSSH to be able to produce private keys
> usable by older OpenSSH as well.

The key encryption for SSH protocol 2 keys is done by OpenSSL's PEM
functions, so AES should be supported by any OpenSSL version that
supports
AES in PEM. IIRC this has been supported for a number of years.

> Any chance of an option in ssh-keygen to specify the cipher? E.g.:

No, I think that would be a microknob that add little value, and
ssh-add
has waaaay to many buttons already.

If we change then it should be to the best encryption that is supported
by
widely deployed SSL/OpenSSH versions.

-d

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[Bug 1550] Move from 3DES to AES-256 for private key encryption [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #3 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:54:39 ---
Message-ID: <4976A70C.2020305@zip.com.au>
Date: Wed, 21 Jan 2009 15:39:40 +1100
From: Darren Tucker <dtucker@zip.com.au>
To: Damien Miller <djm@mindrot.org>
Subject: Re: OpenSSH private key encryption: time for AES?
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
<20090121014237.GD29074@crawfish.ais.com>
<alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
In-Reply-To: <alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
Cc: Jim Knoble <jmknoble@pobox.com>, OpenSSH Devel
<openssh-unix-dev@mindrot.org>

Damien Miller wrote:
[...]
> If we change then it should be to the best encryption that is supported by
> widely deployed SSL/OpenSSH versions.

Don't forget some versions of the Solaris 10 OpenSSL package cripple
all
ciphers with a key length >128 bits. We work around that for the SSH
ciphers but that's not going to help for the OpenSSL PEM functions.

--
Darren Tucker (dtucker at zip.com.au)

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[Bug 1550] Move from 3DES to AES-256 for private key encryption [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #4 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:55:03 ---
Message-ID: <4976A70C.2020305@zip.com.au>
Date: Wed, 21 Jan 2009 15:39:40 +1100
From: Darren Tucker <dtucker@zip.com.au>
To: Damien Miller <djm@mindrot.org>
Subject: Re: OpenSSH private key encryption: time for AES?
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
<20090121014237.GD29074@crawfish.ais.com>
<alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
In-Reply-To: <alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
Cc: Jim Knoble <jmknoble@pobox.com>, OpenSSH Devel
<openssh-unix-dev@mindrot.org>

Damien Miller wrote:
[...]
> If we change then it should be to the best encryption that is supported by
> widely deployed SSL/OpenSSH versions.

Don't forget some versions of the Solaris 10 OpenSSL package cripple
all
ciphers with a key length >128 bits. We work around that for the SSH
ciphers but that's not going to help for the OpenSSL PEM functions.

--
Darren Tucker (dtucker at zip.com.au)

--
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[Bug 1550] Move from 3DES to AES-256 for private key encryption [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #5 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:56:07 ---
Date: Wed, 21 Jan 2009 16:01:35 +1100 (EST)
From: Damien Miller <djm@mindrot.org>
To: Darren Tucker <dtucker@zip.com.au>
Subject: Re: OpenSSH private key encryption: time for AES?
In-Reply-To: <4976A70C.2020305@zip.com.au>
Message-ID: <alpine.BSO.1.10.0901211556540.5581@fuyu.mindrot.org>
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
<20090121014237.GD29074@crawfish.ais.com>
<alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
<4976A70C.2020305@zip.com.au>
Cc: Jim Knoble <jmknoble@pobox.com>, OpenSSH Devel
<openssh-unix-dev@mindrot.org>

On Wed, 21 Jan 2009, Darren Tucker wrote:

> Damien Miller wrote:
> [...]
> > If we change then it should be to the best encryption that is supported by
> > widely deployed SSL/OpenSSH versions.
>
> Don't forget some versions of the Solaris 10 OpenSSL package cripple all
> ciphers with a key length >128 bits. We work around that for the SSH
> ciphers but that's not going to help for the OpenSSL PEM functions.

Shouldn't this Just Work with our replacement EVP_aes_256_cbc in
cipher-aes.c? We already switch it on for the OPENSSL_LOBOTOMISED_AES
case (Obviously it would need to be tested...)

-d

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[Bug 1550] Move from 3DES to AES-256 for private key encryption [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=1550





--- Comment #6 from Jim Knoble <jmknoble@pobox.com> 2009-01-23 07:56:39 ---
Date: Thu, 22 Jan 2009 14:49:01 -0500
From: Jim Knoble <jmknoble@pobox.com>
To: OpenSSH Devel <openssh-unix-dev@mindrot.org>
Subject: Re: OpenSSH private key encryption: time for AES?
Message-ID: <20090122194901.GB22282@crawfish.ais.com>
Mail-Followup-To: OpenSSH Devel <openssh-unix-dev@mindrot.org>
References: <20090120060635.GA29074@crawfish.ais.com>
<alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
<20090121014237.GD29074@crawfish.ais.com>
<alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>
In-Reply-To: <alpine.BSO.1.10.0901211509560.5581@fuyu.mindrot.org>

Circa 2009-01-20 23:16 dixit Damien Miller:

: On Tue, 20 Jan 2009, Jim Knoble wrote:
:
: > $ cat id_rsa-unencrypted |ssh-add /dev/stdin
: > $ ssh-add -l |fgrep /dev/stdin
: > 2048 xx:xx:xx:...:xx:xx:xx /dev/stdin (RSA)
: > $
:
: Does that work without the patch? I don't think it would even with
: the current cipher because it needs to reread the file IIRC.

It's an unpatched ssh-keygen (OpenSSH_4.6p1 Debian-5ubuntu0.6, OpenSSL
0.9.8e 23 Feb 2007).

: > If both operations worked, then one could use an external
: > encryption/decryption facility with one's private keys, e.g.:
: >
: > openssl enc -d -in ~/.ssh/id_rsa -aes-256-cbc |ssh-add
/dev/stdin
: >
: > (although it would take a passphrase to remove a key from
ssh-agent).
:
: Wouldn't this just require the former to work? You'd be passing keys
: to ssh-agent in unencrypted form always, no?

Not sure i understand. The only decryption would happen in the
'openssl | ssh-add' pipeline. In order to know which key to remove,
ssh-add would need to read the unencrypted key, which would only be
available by decrypting it in the pipeline, supplying a passphrase to
the 'openssl' command. Currently, 'ssh-add -d' doesn't require a
passphrase for an OpenSSH-encrypted private key.

I like the flexibility of being able to use stdin with ssh-add (and i
would prefer 'ssh-add -' rather than 'ssh-add /dev/stdin', but
whatever). However, all the above may be moot in light of the
discussion further below.

: The key encryption for SSH protocol 2 keys is done by OpenSSL's PEM
: functions, so AES should be supported by any OpenSSL version that
supports
: AES in PEM. IIRC this has been supported for a number of years.

If older OpenSSH (to a point) would "just work" reading private keys
encrypted with AES-256, then that's fantastic, and no need for any
further options to ssh-keygen.

: If we change then it should be to the best encryption that is
supported by
: widely deployed SSL/OpenSSH versions.

Agreed. Private keys are short, and even if decryption happens
frequently, it takes much longer to enter a passphrase than to decrypt
the key (and both decryption and passphrase can be mitigated via
ssh-agent).

--
jim knoble | jmknoble@pobox.com | http://www.pobox.com/~jmknoble/

--
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