1TANG(8) TANG(8)
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6 tang - Network-Based Cryptographic Binding Server
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9 Tang is a service for binding cryptographic keys to network presence.
10 It offers a secure, stateless, anonymous alternative to key escrow ser‐
11 vices.
12 The Tang project arose as a tool to help the automation of decryption.
14 Existing mechanisms predominantly use key escrow systems where a client
15 encrypts some data with a symmetric key and stores the symmetric key in
16 a remote server for later retrieval. The desired goal of this setup is
17 that the client can automatically decrypt the data when it is able to
18 contact the escrow server and fetch the key.
19 However, escrow servers have many additional requirements, including
21 authentication (so that clients can´t get keys they aren´t suppossed to
22 have) and transport encryption (so that attackers listening on the net‐
23 work can´t eavesdrop on the keys in transit).
24 Tang avoids this complexity. Instead of storing a symmetric key
26 remotely, the client performs an asymmetric key exchange with the Tang
27 server. Since the Tang server doesn´t store or transport symmetric
28 keys, neither authentication nor encryption are required. Thus, Tang is
29 completely stateless and zero-configuration. Further, clients can be
30 completely anonymous.
31 Tang does not provide a client. But it does export a simple REST API
33 and it transfers only standards compliant JSON Object Signing and
34 Encryption (JOSE) objects, allowing you to create your own clients
35 using off the shelf components. For an off-the-shelf automated encryp‐
36 tion framework with support for Tang, see the Clevis project. For the
37 full technical details of the Tang protocol, see the Tang project´s
38 homepage.
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41 Getting a Tang server up and running is simple:
42 $ sudo systemctl enable tangd.socket --now
46 That´s it. The server is now running with a fresh set of cryptographic
50 keys and will automatically start on the next reboot.
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53 Tang intends to be a minimal network service and therefore does not
54 have any configuration. To adjust the network settings, you can over‐
55 ride the tangd.socket unit file using the standard systemd mechanisms.
56 See systemd.unit(5) and systemd.socket(5) for more information.
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59 In order to preserve the security of the system over the long run, you
60 need to periodically rotate your keys. The precise interval at which
61 you should rotate depends upon your application, key sizes and institu‐
62 tional policy. For some common recommendations, see:
63 https://www.keylength.com.
64 To rotate keys, first we need to generate new keys in the key database
66 directory. This is typically /var/db/tang. For example, you can create
67 new signature and exchange keys with the following commands:
68 # DB=/var/db/tang
72 # jose jwk gen -i ´{"alg":"ES512"}´ -o $DB/new_sig.jwk
73 # jose jwk gen -i ´{"alg":"ECMR"}´ -o $DB/new_exc.jwk
74 Next, rename the old keys to have a leading . in order to hide them
78 from advertisement:
79 # mv $DB/old_sig.jwk $DB/.old_sig.jwk
83 # mv $DB/old_exc.jwk $DB/.old_exc.jwk
84 Tang will immediately pick up all changes. No restart is required.
88 At this point, new client bindings will pick up the new keys and old
90 clients can continue to utilize the old keys. Once you are sure that
91 all the old clients have been migrated to use the new keys, you can
92 remove the old keys. Be aware that removing the old keys while clients
93 are still using them can result in data loss. You have been warned.
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96 The Tang protocol is extremely fast. However, in the default setup we
97 use systemd socket activiation to start one process per connection.
98 This imposes a performance overhead. For most deployments, this is
99 still probably quick enough, given that Tang is extremely lightweight.
100 But for larger deployments, greater performance can be achieved.
101 Our recommendation for achieving higher throughput is to proxy traffic
103 to Tang through your existing web services using a connection pool.
104 Since there is one process per connection, keeping a number of connec‐
105 tions open in this setup will enable effective parallelism since there
106 are no internal locks in Tang.
107 For Apache, this is possible using the ProxyPass directive of the
109 mod_proxy module.
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112 Tang provides two methods for building a high availability deployment.
113 1. Client redundency (recommended)
115 2. Key sharing with DNS round-robin
117 While it may be tempting to share keys between Tang servers, this
121 method should be avoided. Sharing keys increases the risk of key com‐
122 promise and requires additional automation infrastructure.
123 Instead, clients should be coded with the ability to bind to multiple
125 Tang servers. In this setup, each Tang server will have its own keys
126 and clients will be able to decrypt by contacting a subset of these
127 servers.
128 Clevis already supports this workflow through its sss plugin.
130 However, if you still feel that key sharing is the right deployment
132 strategy, Tang will do nothing to stop you. Just (securely!) transfer
133 all the contents of the database directory to all your servers. Make
134 sure you don´t forget the unadvertised keys! Then set up DNS
135 round-robin so that clients will be load balanced across your servers.
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138 The Tang server provides no public commands.
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141 Nathaniel McCallum <npmccallum@redhat.com>
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144 systemd.unit(5), systemd.socket(5), jose-jwk-gen(1)
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147 · Clevis : https://github.com/latchset/clevis
148 · Tang : https://github.com/latchset/tang
150 · JOSE : https://datatracker.ietf.org/wg/jose/charter/
152 · mod_proxy : https://httpd.apache.org/docs/2.4/mod/mod_proxy.html
154 June 2017 TANG(8)