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
11 services.
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 supposed to
22 have) and transport encryption (so that attackers listening on the
23 network 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
36 encryption framework with support for Tang, see the Clevis project. For
37 the full technical details of the Tang protocol, see the Tang project’s
38 homepage.
39
41 Getting a Tang server up and running is simple:
42 $ sudo systemctl enable tangd.socket --now
44 That’s it. The server is now running with a fresh set of cryptographic
46 keys and will automatically start on the next reboot.
47
49 Tang intends to be a minimal network service and therefore does not
50 have any configuration. To adjust the network settings, you can
51 override the tangd.socket unit file using the standard systemd
52 mechanisms. See systemd.unit(5) and systemd.socket(5) for more
53 information.
54
56 In order to preserve the security of the system over the long run, you
57 need to periodically rotate your keys. The precise interval at which
58 you should rotate depends upon your application, key sizes and
59 institutional policy. For some common recommendations, see:
60 https://www.keylength.com.
61 There is a convenience script to deal with this. See
63 tangd-rotate-keys(1) for more information. This can also be performed
64 manually as described below.
65 To rotate keys, first we need to generate new keys in the key database
67 directory. This is typically /var/db/tang. For example, you can create
68 new signature and exchange keys with the following commands:
69 # DB=/var/db/tang
71 # jose jwk gen -i '{"alg":"ES512"}' -o $DB/new_sig.jwk
72 # jose jwk gen -i '{"alg":"ECMR"}' -o $DB/new_exc.jwk
73 Next, rename the old keys to have a leading . in order to hide them
75 from advertisement:
76 # mv $DB/old_sig.jwk $DB/.old_sig.jwk
78 # mv $DB/old_exc.jwk $DB/.old_exc.jwk
79 Tang will immediately pick up all changes. No restart is required.
81 At this point, new client bindings will pick up the new keys and old
83 clients can continue to utilize the old keys. Once you are sure that
84 all the old clients have been migrated to use the new keys, you can
85 remove the old keys. Be aware that removing the old keys while clients
86 are still using them can result in data loss. You have been warned.
87
89 The Tang protocol is extremely fast. However, in the default setup we
90 use systemd socket activation to start one process per connection. This
91 imposes a performance overhead. For most deployments, this is still
92 probably quick enough, given that Tang is extremely lightweight. But
93 for larger deployments, greater performance can be achieved.
94 Our recommendation for achieving higher throughput is to proxy traffic
96 to Tang through your existing web services using a connection pool.
97 Since there is one process per connection, keeping a number of
98 connections open in this setup will enable effective parallelism since
99 there are no internal locks in Tang.
100 For Apache, this is possible using the ProxyPass directive of the
102 mod_proxy module.
103
105 Tang provides two methods for building a high availability deployment.
106 1. Client redundancy (recommended)
108 2. Key sharing with DNS round-robin
110 While it may be tempting to share keys between Tang servers, this
112 method should be avoided. Sharing keys increases the risk of key
113 compromise and requires additional automation infrastructure.
114 Instead, clients should be coded with the ability to bind to multiple
116 Tang servers. In this setup, each Tang server will have its own keys
117 and clients will be able to decrypt by contacting a subset of these
118 servers.
119 Clevis already supports this workflow through its sss plugin.
121 However, if you still feel that key sharing is the right deployment
123 strategy, Tang will do nothing to stop you. Just (securely!) transfer
124 all the contents of the database directory to all your servers. Make
125 sure you don’t forget the unadvertised keys! Then set up DNS
126 round-robin so that clients will be load balanced across your servers.
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129 The Tang server provides no public commands.
130
132 Nathaniel McCallum <npmccallum@redhat.com>
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135 systemd.unit(5), systemd.socket(5), jose-jwk-gen(1), tang-show-keys(1),
136 tangd-rotate-keys(1)
137
139 • Clevis : https://github.com/latchset/clevis
140 • Tang : https://github.com/latchset/tang
142 • JOSE : https://datatracker.ietf.org/wg/jose/charter/
144 • mod_proxy : https://httpd.apache.org/docs/2.4/mod/mod_proxy.html
146 12/07/2022 TANG(8)