[ptxdist] [PATCH v2 1/3] openssh: replace dsa with ed25519 host keys

[Clemens Gruber <clemens.gruber@pqgruber.com>]

Changes from v1:
- Rebased after generic -> projectroot rename
- Better explanation in commit message

It is very likely that weak DSA keys are created on embedded
systems due to entropy problems.

I suggest replacing DSA with Ed25519 as second host signature scheme.
Ed25519 performs better, is not as vulnerable to weak random numbers
and the keys can be much smaller, e.g. 256-bit public keys.
DSA and ECDSA fall completely apart when the system has a bad random
number generator, Ed25519 does not.
It is also one of the few elliptic curve cryptography schemes without
magical parameters from NIST or NSA.

Security of 256-bit Ed25519 keys is comparable to 3000-bit RSA keys
and it is immune to most known side-channel / timing attacks.

As the RSA host key is still generated by default, I do not expect
backwards compatibility issues.
It leads to noticeably better performance and higher security, because
the default size of RSA keys is 2048-bit and only 1024-bit for DSA,
whereas Ed25519 is as secure as a 3000-bit RSA key.

For more details, here is the paper:
http://ed25519.cr.yp.to/ed25519-20110926.pdf

Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>

---
 projectroot/etc/rc.once.d/openssh | 8 ++++----
 projectroot/etc/ssh/sshd_config   | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/projectroot/etc/rc.once.d/openssh b/projectroot/etc/rc.once.d/openssh
index 83e6e37..0a63433 100644
--- a/projectroot/etc/rc.once.d/openssh
+++ b/projectroot/etc/rc.once.d/openssh
@@ -3,12 +3,12 @@
 PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
 
 OPENSSH_RSAKEY_DEFAULT="/etc/ssh/ssh_host_rsa_key"
-OPENSSH_DSAKEY_DEFAULT="/etc/ssh/ssh_host_dsa_key"
+OPENSSH_ED25519KEY_DEFAULT="/etc/ssh/ssh_host_ed25519_key"
 
 test -n "$OPENSSH_RSAKEY" || \
 	OPENSSH_RSAKEY=$OPENSSH_RSAKEY_DEFAULT
-test -n "$OPENSSH_DSAKEY" || \
-	OPENSSH_DSAKEY=$OPENSSH_DSAKEY_DEFAULT
+test -n "$OPENSSH_ED25519KEY" || \
+	OPENSSH_ED25519KEY=$OPENSSH_ED25519KEY_DEFAULT
 
 gen_key() {
 
@@ -29,5 +29,5 @@ gen_key() {
 }
 
 gen_key rsa "$OPENSSH_RSAKEY"
-gen_key dsa "$OPENSSH_DSAKEY"
+gen_key ed25519 "$OPENSSH_ED25519KEY"
 
diff --git a/projectroot/etc/ssh/sshd_config b/projectroot/etc/ssh/sshd_config
index 7cd7897..f529fc4 100644
--- a/projectroot/etc/ssh/sshd_config
+++ b/projectroot/etc/ssh/sshd_config
@@ -20,7 +20,7 @@ Protocol 2
 #HostKey /etc/ssh/ssh_host_key
 # HostKeys for protocol version 2
 HostKey /etc/ssh/ssh_host_rsa_key
-HostKey /etc/ssh/ssh_host_dsa_key
+HostKey /etc/ssh/ssh_host_ed25519_key
 
 # Lifetime and size of ephemeral version 1 server key
 #KeyRegenerationInterval 1h
-- 
2.4.4


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