Unable to load public key when encrypting data with openssl

Written by - 1 comments

Published on - Listed in Linux


For an inhouse application I needed to add a monitoring of the login process. Usually that's pretty simple as most systems just use a form with username and password and send a POST of the values. 

But not in this case. I figured that the login procedure was much more complicated:

1) Make a POST request to a URL to retrieve server tokens

2) With the received tokens make yet another POST request and retrieve the string of a public RSA key

3) Encrypt the real password with the received public key and send it with yet another POST request

So far all my steps were working until I needed to encrypt the password with the public key with openssl.
The received public key was saved in a file tmpkey.pub:

$ cat tmpkey.pub
-----BEGIN PUBLIC KEY-----
MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBALdjFsLLaCgRkWaOMLrUPQgGAPM4DXHnq9bAkd1VFwdSIgNkTxY0Bcvr1PxUkNHlYwFjAx/lGEqish6yCgeLURsCAwEAAQ==
-----END PUBLIC KEY-----

I then tried to encrypt the password with this key but it failed:

$ echo "myPassword" | openssl rsautl -encrypt -pubin -inkey tmpkey.pub
unable to load Public Key

Huh? Where did I make the mistake? I came across a blog post (Fun with public keys) by Peter Williams where the author had not the same but a similar problem.
His advice, to verify the public key was a big help though:

$ openssl rsa -text -pubin < tmpkey.pub
unable to load Public Key
139783763789472:error:0906D064:PEM routines:PEM_read_bio:bad base64 decode:pem_lib.c:812:

bad base64 decode! This error message helps!

I found another article from a different blog which had some information how to debug this error. In my case, the number of characters per line exceeded 64 which is a must for openssl - d'uh!

With the command "fold" the output of a file can be cut to a certain number of lines (-w N):

$ fold -w 64 tmpkey.pub
-----BEGIN RSA PUBLIC KEY-----
MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBALdjFsLLaCgRkWaOMLrUPQgGAPM4DXHn
q9bAkd1VFwdSIgNkTxY0Bcvr1PxUkNHlYwFjAx/lGEqish6yCgeLURsCAwEAAQ==
-----END RSA PUBLIC KEY-----

Nice! Now I saved this output in my tmpkey.pub and tried the validation again:

$ openssl rsa -text -pubin < tmpkey.pub
Public-Key: (512 bit)
Modulus:
    00:b7:63:16:c2:cb:68:28:11:91:66:8e:30:ba:d4:
    3d:08:06:00:f3:38:0d:71:e7:ab:d6:c0:91:dd:55:
    17:07:52:22:03:64:4f:16:34:05:cb:eb:d4:fc:54:
    90:d1:e5:63:01:63:03:1f:e5:18:4a:a2:b2:1e:b2:
    0a:07:8b:51:1b
Exponent: 65537 (0x10001)
writing RSA key
-----BEGIN PUBLIC KEY-----
MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBALdjFsLLaCgRkWaOMLrUPQgGAPM4DXHn
q9bAkd1VFwdSIgNkTxY0Bcvr1PxUkNHlYwFjAx/lGEqish6yCgeLURsCAwEAAQ==
-----END PUBLIC KEY-----

Gotcha!

Now I could get back to encrypt the password with the public key:

$ echo "myPassword" | openssl rsautl -encrypt -pubin -inkey tmpkey.pub | base64
WRoZqrXGmcF5/6xTkB437nv+BCqF4XlkEhS6Gx8RIje496tMn/38WOt5QxE8EympP8NsFtVLJxJm
r1/UHkySvw==

 


Add a comment

Show form to leave a comment

Comments (newest first)

Timothy Van Heest from wrote on Sep 14th, 2020:

The `fold` was the trick for me. This seemed to change between openssl versions since I was using a command that worked fine before with the exact same key. Thanks!


RSS feed

Blog Tags:

  AWS   Android   Ansible   Apache   Apple   Atlassian   BSD   Backup   Bash   Bluecoat   CMS   Chef   Cloud   Coding   Consul   Containers   CouchDB   DB   DNS   Database   Databases   Docker   ELK   Elasticsearch   Filebeat   FreeBSD   Galera   Git   GlusterFS   Grafana   Graphics   HAProxy   HTML   Hacks   Hardware   Icinga   Icingaweb   Icingaweb2   Influx   Internet   Java   KVM   Kibana   Kodi   Kubernetes   LVM   LXC   Linux   Logstash   Mac   Macintosh   Mail   MariaDB   Minio   MongoDB   Monitoring   Multimedia   MySQL   NFS   Nagios   Network   Nginx   OSSEC   OTRS   Office   PGSQL   PHP   Perl   Personal   PostgreSQL   Postgres   PowerDNS   Proxmox   Proxy   Python   Rancher   Rant   Redis   Roundcube   SSL   Samba   Seafile   Security   Shell   SmartOS   Solaris   Surveillance   Systemd   TLS   Tomcat   Ubuntu   Unix   VMWare   VMware   Varnish   Virtualization   Windows   Wireless   Wordpress   Wyse   ZFS   Zoneminder   


Update cookies preferences