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

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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 This patch should not make problems except for very outdated OpenSSH clients (older than 6.x) or PuTTY versions.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@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@openssh.

com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192- ctr,aes128-ctr\

• 	MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-et
  

m@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@ openssh.com\

• 	KexAlgorithms curve25519-sha256@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@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192- ctr,aes128-ctr\

• 	MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-et
  

m@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@ openssh.com\

• 	KexAlgorithms curve25519-sha256@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