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1 <?xml version='1.0' encoding="UTF-8"?>
2 <?xml-stylesheet href="/xsl/guide.xsl" type="text/xsl"?>
3 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
4
5 <guide disclaimer="obsolete" redirect="http://wiki.gentoo.org/wiki/Project:Infrastructure/SSH_Key_Guide">
6 <title>SSH access to cvs.gentoo.org</title>
7
8 <author title="Author">
9 <mail link="swift"/>
10 </author>
11 <author title="Author">
12 <mail link="robbat2"/>
13 </author>
14 <author title="Author">
15 <mail link="antarus"/>
16 </author>
17 <author title="Editor">
18 <mail link="nightmorph"/>
19 </author>
20
21 <abstract>
22 This mini-guide explains on how to create and use ssh-keys, especially
23 for use on cvs.gentoo.org.
24 </abstract>
25
26 <version>1.4</version>
27 <date>2012-05-28</date>
28
29 <chapter>
30 <title>SSH keys</title>
31 <section>
32 <title>Key Handling</title>
33 <body>
34 <p>
35 Your SSH keypair authenticates you to Gentoo Infrastructure. Properly
36 handling these keys is vital to keeping our machines safe. Please try to
37 follow these guidelines:
38 </p>
39
40 <ul>
41 <li>Place your private keys <b>only</b> on machines you trust. This means only you have root
42 on these machines and they are not shared with other users.
43 </li>
44 <li>Do not trust Gentoo Infrastructure. Do not place copies of your keys
45 on Gentoo machines (like dev.gentoo.org.) You may forward your SSH agent
46 through Gentoo managed machines if they are configured to allow users to
47 agent forward (more on forwarding later.)
48 </li>
49 <li>Encrypt your keys with a strong passphrase. If you have trouble making
50 a passphrase try emerge pwgen; pwgen -sB 25
51 </li>
52 <li>Do not access Gentoo infrastructure from untrusted machines such as business
53 kiosks at hotels, internet cafes, or machines at computer conferences. Many of these machines
54 are infected with malware.</li>
55 <li>If you believe your keys were compromised, contact infrastructure immediately.
56 You can do this via #gentoo-infra on irc.freenode.net or by emailing incidents@gentoo.org.
57 </li>
58 <li>Official hostkey fingerprints for Gentoo Infrastructure servers are
59 available on the <uri link="/proj/en/infrastructure/server-specs"> server
60 specifications </uri> page.
61 </li>
62 </ul>
63 </body>
64 </section>
65 <section>
66 <title>Creating the SSH keys</title>
67 <body>
68
69 <p>
70 First of all, be physically logged on to your own computer. Make sure
71 that no-one will see you typing stuff in, since we are going to type in
72 passphrases and such. So get your pepperspray and fight all untrusted
73 entities until you are home alone.
74 </p>
75
76 <p>
77 Now we are going to create our ssh keys, RSA keys to be exact. The key should
78 be at least 2048 bits in length, but 4096 bits is recommended. Log onto
79 your computer as the user that you are going to be using when you want
80 to access cvs.gentoo.org. Then issue <c>ssh-keygen -t rsa -b 4096</c>:
81 </p>
82
83 <pre caption="Creating SSH keys">
84 $ <i>ssh-keygen -t rsa -b 4096</i>
85 Generating public/private rsa key pair.
86 Enter file in which to save the key (/home/temp/.ssh/id_rsa): <comment>(Press enter)</comment>
87 Created directory '/home/temp/.ssh'.
88 Enter passphrase (empty for no passphrase): <comment>(Enter your passphrase)</comment>
89 Enter same passphrase again: <comment>(Enter your passphrase again)</comment>
90 Your identification has been saved in /home/temp/.ssh/id_rsa.
91 Your public key has been saved in /home/temp/.ssh/id_rsa.pub.
92 The key fingerprint is:
93 85:35:81:a0:87:56:78:a2:da:53:6c:63:32:d1:34:48 user@examplehost <comment>This is the fingerprint of your new key</comment>
94 </pre>
95
96 <note>
97 Please be sure to set a strong passphrase on your private key. Ideally,
98 this passphrase should be at least eight characters and contain a mixture of
99 letters, numbers and symbols.
100 </note>
101
102 <warn>
103 Do not set an empty passphrase on your ssh key. If infra finds out this is the
104 case; your account will be suspended.
105 </warn>
106
107 <pre caption="Created files">
108 # <i>ls ~/.ssh</i>
109 id_rsa id_rsa.pub
110 </pre>
111
112 <p>
113 You may have more files than this, but the two files listed above
114 are the ones that are really important.
115 </p>
116
117 <p>
118 The first file, <path>id_rsa</path>, is your <e>private</e> key. Don't
119 give this to anyone; never decrypt it on an untrusted machine. Gentoo Staff
120 will never ask you for a copy of your private key.
121 </p>
122
123 <warn>
124 Be very careful which machines you put your private key on. If you have
125 several (<e>trusted!</e>) hosts from which you want to connect to
126 cvs.gentoo.org, you should copy <path>id_rsa</path> to the
127 <path>~/.ssh</path> directories on those hosts. Trusted machines are machines
128 that only you have root on; these machines are not shared with other users.
129 </warn>
130
131 <p>
132 The second file, <path>id_rsa.pub</path>, is your <e>public</e> key.
133 Distribute this file amongst all hosts that you want to be able to
134 access through SSH pubkey authentification. This file should be appended
135 to <path>~/.ssh/authorized_keys</path> on those remote hosts. Also add it
136 to your local host so you can connect to that one too if you have several
137 boxes.
138 </p>
139
140 <pre caption="Adding the SSH key to the box">
141 $ <i>cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys</i>
142 </pre>
143
144 </body>
145 </section>
146 <section>
147 <title>
148 Installing your public key on a machine using LDAP authentication for SSH
149 </title>
150 <body>
151
152 <note>
153 If you are a new developer, your recruiter will put your first SSH key into
154 LDAP, so that you can login. You can then add any additional SSH keys yourself
155 using the following procedure.
156 </note>
157
158 <note>
159 For most of the Gentoo infrastructure, we use LDAP to distribute user
160 information including SSH public keys. On these machines,
161 <path>~/.ssh/authorized_keys</path> should generally not contain your key.
162 </note>
163
164 <p>
165 You should place your public key into LDAP, using
166 <path>perl_ldap</path>, or <path>ldapmodify</path> directly.
167 The Infrastructure <uri link="/proj/en/infrastructure/ldap.xml">LDAP
168 guide</uri> describes this in more detail.
169 </p>
170
171 <pre caption="Adding the SSH key with perl_ldap on dev.gentoo.org">
172 $ <i>perl_ldap -b user -C sshPublicKey "$(cat ~/.ssh/id_rsa.pub)" &lt;username&gt;</i>
173 </pre>
174
175 <warn>
176 Each <path>sshPublicKey</path> attribute must contain exactly one public key. If you have multiple public keys, you must have multiple attributes!
177 </warn>
178
179 </body>
180 </section>
181 <section>
182 <title>Using keychain</title>
183 <body>
184
185 <p>
186 Every time you want to log on to a remote host using SSH public key
187 authentification, you will be asked to enter your passphrase. As much as
188 everybody likes typing, too much is sometimes too much. Luckily, there is
189 <c>keychain</c> to the rescue. There is an document on this one <uri
190 link="/doc/en/keychain-guide.xml">here</uri>, but I'll give you a quick
191 introduction.
192 </p>
193
194 <p>
195 First, install <c>keychain</c>:
196 </p>
197
198 <pre caption="Installing keychain">
199 # <i>emerge keychain</i>
200 </pre>
201
202 <p>
203 Now have keychain load up your private ssh key when you log on to your local
204 box. To do so, add the following to <path>~/.bash_profile</path>. Again, this
205 should be done on your <e>local</e> machine where you work at the Gentoo CVS.
206 </p>
207
208 <warn>
209 <b>NEVER</b> run keychain or decrypt your private key on an untrusted host.
210 </warn>
211
212 <pre caption="Add this to .bash_profile">
213 keychain ~/.ssh/id_rsa
214 . .keychain/<comment>hostname</comment>-sh
215 </pre>
216
217 <p>
218 Be sure to substitute <c>hostname</c> with your hostname.
219 </p>
220
221 </body>
222 </section>
223 </chapter>
224 </guide>

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