Re: [PATCH 3/3] OpenSSH: use safer cryptography defaults

[Michael Tremer <michael.tremer@ipfire.org>]

[-- Attachment #1: Type: text/plain, Size: 5459 bytes --]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

On Wed, 2018-05-16 at 17:39 +0200, Peter Müller wrote:
> Hello *,
> 
> could somebody have a look at this sometimes?
> 
> If possible, I'd like to add this to the upcoming Core 121, too
> - in case we are not becoming too big with the new kernel already.

I don't think that this will find space in C121.

> Thanks, and best regards,
> Peter Müller
> 
> 
> > By default, OpenSSH uses crypto algorithms such as SHA1, which are
> > considered insecure and should not be used anymore. This patch
> > updates the used ciphers, message-digest algorithms and key exchange
> > algorithms according https://stribika.github.io/2015/01/04/secure-secure-she
> > ll.html .
> > 
> > For the kex algo "diffie-hellman-group-exchange-sha256", an intact
> > SSH moduli file is required. To make sure we are not falling back
> > to insecure crypto here, its presence is checked at SSH startup.
> > 
> > On my machines, this file was already there, but it makes sense to
> > me to double-check this. This patch should not make problems except
> > for very outdated OpenSSH clients (older than 6.x) or PuTTY versions.
> > 
> > This partially addresses #11538 and requires patch 2/3.
> > 
> > Signed-off-by: Peter Müller <peter.mueller(a)link38.eu>
> > ---
> >  config/rootfiles/core/121/update.sh |  6 +++++-
> >  lfs/openssh                         |  4 ++++
> >  src/initscripts/system/sshd         | 12 ++++++++++++
> >  3 files changed, 21 insertions(+), 1 deletion(-)
> > 
> > diff --git a/config/rootfiles/core/121/update.sh
> > b/config/rootfiles/core/121/update.sh
> > index 3ec251292..99c174156 100644
> > --- a/config/rootfiles/core/121/update.sh
> > +++ b/config/rootfiles/core/121/update.sh
> > @@ -60,7 +60,11 @@ rm -rvf \
> >  sed -i /etc/ssh/sshd_config \
> >  	-e 's/^#SyslogFacility AUTH$/SyslogFacility AUTH/' \
> >  	-e 's/^#LogLevel INFO$/LogLevel INFO/' \
> > -	-e 's/^#StrictModes .*$/StrictModes yes/'
> > +	-e 's/^#StrictModes .*$/StrictModes yes/' \
> > +	-e 's/^#RekeyLimit default none$/Ciphers chacha20-poly1305(a)openssh.
> > com,aes256-gcm(a)openssh.com,aes128-gcm(a)openssh.com,aes256-ctr,aes192-
> > ctr,aes128-ctr\
> > +			MACs hmac-sha2-512-etm(a)openssh.com,hmac-sha2-256-et
> > m(a)openssh.com,umac-128-etm(a)openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@
> > openssh.com\
> > +			KexAlgorithms curve25519-sha256(a)libssh.org,diffie-
> > hellman-group-exchange-sha256\
> > +			#RekeyLimit default none/'
> >  
> >  # Start services
> >  /etc/init.d/sshd restart
> > diff --git a/lfs/openssh b/lfs/openssh
> > index 7e8468ac9..3043501a2 100644
> > --- a/lfs/openssh
> > +++ b/lfs/openssh
> > @@ -96,6 +96,10 @@ $(TARGET) : $(patsubst %,$(DIR_DL)/%,$(objects))
> >  		-e 's/^#\?AllowTcpForwarding .*$$/AllowTcpForwarding no/' \
> >  		-e 's/^#\?PermitRootLogin .*$$/PermitRootLogin yes/' \
> >  		-e 's/^#StrictModes .*$/StrictModes yes/' \
> > +		-e 's/^#RekeyLimit default none$/Ciphers chacha20-poly1305@
> > openssh.com,aes256-gcm(a)openssh.com,aes128-gcm(a)openssh.com,aes256-ctr,aes192-
> > ctr,aes128-ctr\
> > +			MACs hmac-sha2-512-etm(a)openssh.com,hmac-sha2-256-et
> > m(a)openssh.com,umac-128-etm(a)openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@
> > openssh.com\
> > +			KexAlgorithms curve25519-sha256(a)libssh.org,diffie-
> > hellman-group-exchange-sha256\
> > +			#RekeyLimit default none/' \
> >  		-e 's|^#\?HostKey /etc/ssh/ssh_host_dsa_key$$||' \
> >  		-e 's|^#\?HostKey /etc/ssh/ssh_host_ecdsa_key$$||' \
> >  		-e 's|^#\?HostKey /etc/ssh/ssh_host_ed25519_key$$||' \
> > diff --git a/src/initscripts/system/sshd b/src/initscripts/system/sshd
> > index 7b4092d38..d7958e800 100644
> > --- a/src/initscripts/system/sshd
> > +++ b/src/initscripts/system/sshd
> > @@ -23,6 +23,18 @@ case "$1" in
> >  		evaluate_retval
> >  	done
> >  
> > +	# Make sure moduli file is properly present
> > +	# (https://stribika.github.io/2015/01/04/secure-secure-shell.html)
> > +	modulifile="/etc/ssh/moduli"
> > +	if [ ! -e "${modulifile}" ]; then
> > +		boot_mesg "Generating SSH moduli file (this may take a
> > while)..."
> > +
> > +		ssh-keygen -G /etc/ssh/moduli.all -b 4096
> > +		ssh-keygen -T /etc/ssh/moduli.safe -f /etc/ssh/moduli.all
> > +		mv /etc/ssh/moduli.safe /etc/ssh/moduli
> > +		rm -f /etc/ssh/moduli.all
> > +	fi
> > +
> >          [ -e "/var/ipfire/remote/enablessh" ] || exit 0 # SSH is not
> > enabled
> >          boot_mesg "Starting SSH Server..."
> >          loadproc /usr/sbin/sshd 
> > 
> 
> 
-----BEGIN PGP SIGNATURE-----
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=WzL5
-----END PGP SIGNATURE-----