ssh-add from bash script and automate passphrase entry

Question

I am trying to do ssh-add from script (don't care about about security at the moment).

Now ssh prompts for passphrase, which needs to be automated, so i read couple of things like this and found expect.

And now i do following:

eval `ssh-agent -s`

script tmp.sh defined as :

#!/usr/bin/expect
spawn ssh-add /root/.ssh/id_rsa
expect "Enter passphrase for /root/.ssh/id_rsa:"
send "my_pass"
interact

./tmp.sh

ssh-add -l

If ssh-add would have worked it shows something like

4096 SHA256:wlfP/nhVSWXLcljBOen5GSYZXJGgfi/XJWfZeBwqRsM id_rsa (RSA)

But instead i get The agent has no identities. Seems like ssh-agent looses it's context.

Am open to other solutions to do this.

Answer 1

Personally, I find the use of expect a bit cumbersome. The following approach found how to make ssh-add read passphrase from a file rather informative.

So if your version of ssh-add allows the -p argument and you are not worried about security then this should work:

#!/bin/bash
# store a file somewheres with your passphrase. For example's sake
# I'll just use $HOME/.myscrt

<$HOME/.myscrt ssh-add -p ~/.ssh/id_rsa

Now if -p is not an option for you, I found the second method mildly ingenious:

#!/bin/bash
# Same passfile and some minor enhancements from the OP of the linked
# solution
PASS="$(<$HOME/.myscrt)"

# the following is just a one-liner method of making an executable
# one-line script echoing the password to STDOUT
install -vm700 <(echo "echo $PASS") "$PWD/ps.sh"

# then the magic happens. NOTE: your DISPLAY variable should be set
# for this method to work (see ssh-add(1))
[[ -z "$DISPLAY" ]] && export DISPLAY=:0
< id_rsa SSH_ASKPASS="$PWD/ps.sh" ssh-add - && shred -n3 -uz  $PWD/ps.sh    

When I tested the script I called "j", see below:

$ cd /tmp
$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/me/.ssh/id_rsa): /tmp/id_rsa
Enter passphrase (empty for no passphrase): asdfasdf
Enter same passphrase again: asdfasdf
Your identification has been saved in /tmp/id_rsa.
Your public key has been saved in /tmp/id_rsa.pub.
The key fingerprint is:
ed:1a:ae:c7:ac:47:5e:31:98:8e:18:8f:1c:67:94:6d jimconn@redapt-240
The key's randomart image is:
+--[ RSA 2048]----+
|       o         |
|      o E        |
|     . . o       |
|    o o o.o      |
|   . O oS .o     |
|    + o o..      |
|       =...      |
|       .*o       |
|      o=o        |
+-----------------+
$ echo 'asdfasdf' > ~/.myscrt
$ chmod 0600 ~/.myscrt
$ ls -altr ~/.myscrt
-rw------- 1 me me 9 Feb 16 19:00 /home/me/.myscrt
$ cat ~/.myscrt
asdfasdf
$ ls -ltr
total 12
-rw-r--r-- 1 me me  400 Feb 16 18:59 id_rsa.pub
-rw------- 1 me me 1766 Feb 16 18:59 id_rsa
-rwx------ 1 me me  151 Feb 16 19:04 j
$ cat j
#!/bin/bash
PASS="$(<$HOME/.myscrt)"
install -vm700 <(echo "echo $PASS") "$PWD/ps.sh"
cat id_rsa | SSH_ASKPASS="$PWD/ps.sh" ssh-add - && shred -n3 -uz     $PWD/ps.sh
$ ./j
‘/dev/fd/63’ -> ‘/tmp/so/ps.sh’
Identity added: (stdin) ((stdin))
$ ls
id_rsa  id_rsa.pub  j

So, one thing to quickly note about this method is that listing the identities loaded into ssh-agent will only show that stdin was loaded:

$ ssh-add -D
All identities removed.
$ ssh-add -l
2048 ed:1a:ae:c7:ac:47:5e:31:98:8e:18:8f:1c:67:94:6d (stdin) (RSA)
$ ./j
‘/dev/fd/63’ -> ‘/tmp/so/ps.sh’
Identity added: (stdin) ((stdin))
$ ssh-add -l
2048 ed:1a:ae:c7:ac:47:5e:31:98:8e:18:8f:1c:67:94:6d (stdin) (RSA)