Elliptic Curve host key and -R argument bug
Bruno Thomsen
bth at kamstrup.dk
Tue Jan 28 22:18:44 WST 2014
Hi,
I have observed some strange dropbear behavior with the -R argument (Create hostkeys as required) and Elliptic Curve host keys.
The result is an extremely large temporary host key file (multiple megabytes).
SSH client: Google Chrome extension: Secure Shell 0.8.25
1) Connect to dropbear running without arguments and a single host key (ecdsa-sha2-nistp521) in /etc/dropbear/dropbear_ecdsa_host_key
2) Stop dropbear
3) Remove old host key and generate a single new host key (ecdsa-sha2-nistp256) in /etc/dropbear/dropbear_ecdsa_host_key
4) Start dropbear with -R argument
5) Reconnect to dropbear and it generate an extremely large host key (process never ends).
Result:
root at target:~ ll /etc/dropbear/
total 54508
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 55593054 Jan 28 13:39 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 66001
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 67316589 Jan 28 13:40 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 70657
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 72064080 Jan 28 13:40 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 84631
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 86317002 Jan 28 13:40 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 129200
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 131778657 Jan 28 13:41 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 130372
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 132973731 Jan 28 13:41 dropbear_ecdsa_host_key.tmp377
root at target:~ ll /etc/dropbear/
total 131219
dr-------- 2 root root 1024 Jan 28 13:38 .
drwxrwxr-x 19 root root 1024 Jan 28 12:09 ..
-r-------- 1 root root 140 Jan 28 13:35 dropbear_ecdsa_host_key
-rw------- 1 root root 133837839 Jan 28 13:41 dropbear_ecdsa_host_key.tmp377
root at target:~ top
Mem: 121580K used, 3376K free, 0K shrd, 10172K buff, 91900K cached
CPU: 20.0% usr 80.0% sys 0.0% nic 0.0% idle 0.0% io 0.0% irq 0.0% sirq
Load average: 2.30 1.04 0.52 2/55 1416
PID PPID USER STAT VSZ %MEM CPU %CPU COMMAND
377 31162 root R 2292 1.8 0 66.5 dropbear -R
Maybe it's a collision in /etc/dropbear/dropbear_ecdsa_host_key that holds an ecdsa-sha2-nistp256 and when dropbear tries to generate a new ecdsa-sha2-nistp521.
Venlig hilsen / Best regards
Kamstrup A/S <http://www.kamstrup.dk>
Bruno Thomsen
Development engineer
Technology
Kamstrup A/S
Industrivej 28
DK-8660 Skanderborg
Tel: +45 89 93 10 00
Fax: +45 89 93 10 01
Dir: +45 89 93 13 94
E-mail: bth at kamstrup.dk
Web: www.kamstrup.dk
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