Arvutiklassi vanad arvutid

2023-08-15T12:31:15Z

Marek:

__TOC__

=== Vanad ICT-501 klassi arvutid ===

33 komplekti: arvuti + monitor + klaviatuur + hiir.

Järgi on: 33 arvutit 31 monitori

==== Arvuti ====
'HP EliteDesk 800 G3 SFF'
* i5-7500 CPU
* 16GB RAM
* NVIDIA GT720 GPU
* 512GB SSD, suht surnud (kulunud)
* 1TB 5200RPM 'green' HDD, super aeglane
==== Monitor ====
'Monitor AOC U2879VF 28" 4K'
* 28" ekraani diameeter
* 3840x2160 resolutsioon
* HDMI input
* DP input
* VGA input
* DVI input

=== Soovijad ===

* Katrin Tõemets : 1 komplekt. Käes: 1 monitor, arvuti on ootel.
* Mohammad Hasan Ahmadilivani : 1 monitor. Käes: 1 monitor.

2020-09-10T16:11:00Z

Marek:

__TOC__

=RRDTOOL=

==ERROR: could not lock RRD==

Appears due to broken NFS locks

Usually after abnormal network outage between NFS storage server and client system where RRDTOOL works

===Fix===
<code>
mv dbase.rrd dbase.rrd.old

cp dbase.rrd.old dbase.rrd

rm dbase.rrd.old

</code>

===Another fix===
restart both systems

RRDTool

2020-09-10T16:10:44Z

Marek:

2019-12-04T15:17:11Z

Marek:

__TOC__

Tutorial on how to encrypt and decrypt small messages using Secure Shell keys

== Why? ==
For example,<br>
when You have to send someone a password and sending it over internet in plaintext is out of the question.

== How to send Yourself a secret message (tutorial) ==

=== The keys ===

Everyone who uses Secure Shell (SSH) has an easy access to accompanying Secure Shell keys. When You do not have them, then You generate them.

All it takes is Linux, MacOS command line or Cygwin shell in Windows. A minute or two of Your time and few sips of tea. Done.

One can make simple passwordless RSA key-pair with <code>ssh-keygen</code> utility like this:
<pre>
linux:/home/user> ssh-keygen -t rsa -b 4096
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:seDs6vDo55WegAZnG/mr8S+sgz2kvJFCc1wAGsHyB2c user@linux
The key's randomart image is:
+---[RSA 4096]----+
|+o.. |
|oo. E |
|o. + .. . |
| o.oo . o |
|.o=+ o S |
|.+== . . |
|oB*.o + |
|+o=*+* . |
| o*OBo+ |
+----[SHA256]-----+
</pre>

The process above creates 2 files <code>id_rsa</code> <code>id_rsa.pub</code> and places them into subfolder <code>.ssh</code> relative to Your home directory.

The contents of the public key <code>id_rsa.pub</code> should be like this:
<pre>
ssh-rsa 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 user@linux
</pre>

And the contents of the private key <code>id_rsa</code> should be like this:
<div class="toccolours mw-collapsible mw-collapsed" style="width:540px; overflow:auto;">
<div style="font-weight:bold;line-height:1.6;">SSH private key, file <code>id_rsa</code> contents</div>
<div class="mw-collapsible-content">
<pre>
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
</pre>
</div></div>

=== To encrypt ===

Now You have Your pair of keys, the public one <code>id_rsa.pub</code> is used to encrypt and the private one <code>id_rsa</code> to decrypt a message.

==== Create the message ====

Take Your favorite text editor and create short text file <code>message.txt</code> with some content like:
<pre>
This is very serious short message.
That will be encrypted.
And decrypted.
</pre>

==== Prepare Your public key for encryption ====

One drawback or discouraging step for encryption is that Your public key is not usable '''''as is'''''.

To be usable with <code>openssl</code> utility it has to be in PKCS8 format.

Public key can be converted to PKCS8 format with <code>ssh-keygen</code> utility like this:
<pre>
linux:/home/user> ssh-keygen -f ~/.ssh/id_rsa.pub -e -m pkcs8 > id_rsa_pub.pkcs8
</pre>

The contents of such converted key should be like this:
<pre>
-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----
</pre>

==== Encrypt the message ====

Now You can encrypt Your super secret message with converted public key like this:
<pre>
linux:/home/user> cat message.txt | openssl rsautl -encrypt -pubin -inkey id_rsa_pub.pkcs8 > message.enc
</pre>
In above example we pipe the contents of <code>message.txt</code> file to <code>openssl</code> utility that uses converted public key <code>id_rsa_pub.pkcs8</code> and then we store the output in file <code>message.enc</code>

=== To decrypt ===

To decrypt the encrypted message file <code>message.enc</code> we use <code>openssl</code> utility like this:
<pre>
linux:/home/user> cat message.enc | openssl rsautl -decrypt -inkey ~/.ssh/id_rsa
This is very serious short message.
That will be encrypted.
And decrypted.
</pre>
In above example the contents of decrypted message are show in startard output.

To save decrypted contents one can modify the command like this:
<pre>
linux:/home/user> cat message.enc | openssl rsautl -decrypt -inkey ~/.ssh/id_rsa > message.txt
</pre>

== Real world ==

In real world, when You have to pass someone sensitive small message, like a password
# You ask that someone to send You their public key
#* If that public key is not already in PKCS8 format then You convert it
# You encrypt Your message with that someone's public key that is in PKCS8 format
# You send the encrypted message to that someone
# That someone decrypts Your message with their private key
Contrary to tutorial above Your SSH keys are not needed when You are sending an encrypted message. You only need the other persons public key.

<hr>
When someone sends You their public key, save it to a file <code>someone.pub</code>. Create Your secret message <code>message.txt</code>. Then do following, firstly to convert the key and secondly to encrypt Your message:
<pre>
linux:/home/user> ssh-keygen -f someone.pub -e -m pkcs8 > someone_pub.pkcs8
linux:/home/user> cat message.txt | openssl rsautl -encrypt -pubin -inkey someone_pub.pkcs8 > message.enc
</pre>
And send the output <code>message.enc</code> as a file to that someone.

That person then does following and reads the message content from standard output:
<pre>
linux:/home/someone> cat message.enc | openssl rsautl -decrypt -inkey ~/.ssh/id_rsa
This is very serious short message.
That will be encrypted.
And decrypted.
</pre>
<hr>

== Notes ==

=== Message size ===

This encryption / decryption method is suitable for small messages, messages whose bitlength is smaller than used RSA key length.

If You want to encrypt longer messages or some big file(s) then the above method can be used for passing on encrypted passwords that are used for file encryption/decryption.

One should use CBC (Cipher Block Chaining) continuous block cipher like AES256 for big file encryption / decryption. <code>openssl</code> utility is able to do that too.
<pre>
openssl enc -aes256 -kfile message.txt -in file -out file.enc
</pre>

=== What the path? ===

<code>~</code> denotes users home directory, in essence its a shortcut for <code>/home/user</code>

Then <code>~/.ssh</code> means subfolder <code>.ssh</code> that resides in users home directory <code>/home/user</code>

When using full path the above would be <code>/home/user/.ssh</code>

=== Private stuff ===

Your key pair that You generated is Your sensitive security information.

Your public key can be passed on to persons/organizations You know, to authenticate You as a sign-on method (go see Gitlab), or it can be used as in above tutorial to encrypt messages. Being "public" does not mean You should openly advertise the contents of that key. It is theoretically possible to re-create private key based on public key, that process takes massive amounts of supercomputer time and is exponentially difficult based on key length. The longer the key the better. There is a tradeoff - longer keys work slower. In above tutorial we used 4096 bit keys that are quite okay by todays (2019) standards.

Your private key should never be shown or given out to anyone. The best practice is to encrypt Your private key with a password.
<code>ssh-keygen</code> utility is able to do that like this:<pre>
linux:/home/user> ssh-keygen -p -f ~/.ssh/id_rsa
Enter new passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved with the new passphrase.
</pre>

When You lose your private key, then all is lost. Unless You work for NSA and have supercomputer farm at hand. So keep it safe and secure.

=== Martian messages ===

Obviously encrypted messages are not human readable. If You made a mistake of looking the contents and Your command line went gibberish, issue following command by blindly typing: <code>reset</code>. This resets the terminal and You should see normal command line again.