1CRYPTO-POLICIES(7) CRYPTO-POLICIES(7)
2
6 crypto-policies - system-wide crypto policies overview
7
9 The security of cryptographic components of the operating system does
10 not remain constant over time. Algorithms, such as cryptographic
11 hashing and encryption, typically have a lifetime, after which they are
12 considered either too risky to use or plain insecure. That means, we
13 need to phase out such algorithms from the default settings or
14 completely disable them if they could cause an irreparable problem.
15 While in the past the algorithms were not disabled in a consistent way
17 and different applications applied different policies, the system-wide
18 crypto-policies followed by the crypto core components allow
19 consistently deprecating and disabling algorithms system-wide.
20 Several preconfigured policies (DEFAULT, LEGACY, FUTURE, and FIPS) and
22 subpolicies are included in the crypto-policies(7) package. System
23 administrators or third-party vendors can define custom policies and
24 subpolicies.
25 The recommended way to modify the effective configuration is to apply a
27 custom subpolicy on top of a predefined policy. This allows
28 configuration to evolve with future updates of the predefined policies
29 keeping desired modification in place. Modifying effective
30 configuration by defining a fully custom policy prevents the
31 configuration from evolving with future updates of the predefined
32 policies. The syntax to define custom policies and subpolicies is
33 described in the CRYPTO POLICY DEFINITION FORMAT section below.
34 For rationale, see RFC 7457 for a list of attacks taking advantage of
36 legacy crypto algorithms.
37
39 Crypto-policies apply to the configuration of the core cryptographic
40 subsystems, covering TLS, IKE, IPSec, DNSSec, and Kerberos protocols;
41 i.e., the supported secure communications protocols on the base
42 operating system.
43 Once an application runs in the operating system, it follows the
45 default or selected policy and refuses to fall back to algorithms and
46 protocols not within the policy, unless the user has explicitly
47 requested the application to do so. That is, the policy applies to the
48 default behavior of applications when running with the system-provided
49 configuration but the user can override it on an application-specific
50 basis.
51 The policies currently provide settings for these applications and
53 libraries:
54 • BIND DNS name server daemon (scopes: BIND, DNSSec)
56 • GnuTLS TLS library (scopes: GnuTLS, SSL, TLS)
58 • OpenJDK runtime environment (scopes: java-tls, SSL, TLS)
60 • Kerberos 5 library (scopes: krb5, Kerberos)
62 • Libreswan IPsec and IKE protocol implementation (scopes: libreswan,
64 IPSec, IKE)
65 • NSS TLS library (scopes: NSS, SSL, TLS)
67 • OpenSSH SSH2 protocol implementation (scopes: OpenSSH, SSH)
69 • OpenSSL TLS library (scopes: OpenSSL, SSL, TLS)
71 • libssh SSH2 protocol implementation (scopes: libssh, SSH)
73 Applications using the above libraries and tools are covered by the
75 cryptographic policies unless they are explicitly configured otherwise.
76
78 LEGACY
79 This policy ensures maximum compatibility with legacy systems; it
80 is less secure and it includes support for TLS 1.0, TLS 1.1, and
81 SSH2 protocols or later. The algorithms DSA and 3DES are allowed,
82 while RSA and Diffie-Hellman parameters are accepted if larger than
83 1024 bits. This policy provides at least 64-bit security.
84 • MACs: all HMAC with SHA-1 or better + all modern MACs (Poly1305
86 etc.)
87 • Curves: all prime >= 255 bits (including Bernstein curves)
89 • Signature algorithms: with SHA1 hash or better (DSA allowed)
91 • TLS Ciphers: all available >= 112-bit key, >= 128-bit block
93 (including 3DES, excluding RC4)
94 • Non-TLS Ciphers: same as TLS ciphers with added Camellia
96 • Key exchange: ECDHE, RSA, DHE
98 • DH params size: >= 1024
100 • RSA keys size: >= 1024
102 • DSA params size: >= 1024
104 • TLS protocols: TLS >= 1.0, DTLS >= 1.0
106 DEFAULT
108 The DEFAULT policy is a reasonable default policy for today’s
109 standards. It allows the TLS 1.2, and TLS 1.3 protocols, as well as
110 IKEv2 and SSH2. The Diffie-Hellman parameters are accepted if they
111 are at least 2048 bits long. This policy provides at least 112-bit
112 security with the exception of allowing SHA-1 signatures in DNSSec
113 where they are still prevalent.
114 • MACs: all HMAC with SHA-1 or better + all modern MACs (Poly1305
116 etc.)
117 • Curves: all prime >= 255 bits (including Bernstein curves)
119 • Signature algorithms: with SHA-224 hash or better (no DSA)
121 • TLS Ciphers: >= 128-bit key, >= 128-bit block (AES, ChaCha20,
123 including AES-CBC)
124 • non-TLS Ciphers: as TLS Ciphers with added Camellia
126 • key exchange: ECDHE, RSA, DHE (no DHE-DSS)
128 • DH params size: >= 2048
130 • RSA keys size: >= 2048
132 • TLS protocols: TLS >= 1.2, DTLS >= 1.2
134 NEXT
136 The NEXT policy is just an alias to the DEFAULT policy.
137 FUTURE
139 A conservative security policy that is believed to withstand any
140 near-term future attacks. This policy does not allow the use of
141 SHA-1 in signature algorithms. The policy also provides some (not
142 complete) preparation for post-quantum encryption support in form
143 of 256-bit symmetric encryption requirement. The RSA and
144 Diffie-Hellman parameters are accepted if larger than 3071 bits.
145 This policy provides at least 128-bit security.
146 • MACs: all HMAC with SHA-256 or better + all modern MACs
148 (Poly1305 etc.)
149 • Curves: all prime >= 255 bits (including Bernstein curves)
151 • Signature algorithms: with SHA-256 hash or better (no DSA)
153 • TLS Ciphers: >= 256-bit key, >= 128-bit block, only
155 Authenticated Encryption (AE) ciphers
156 • non-TLS Ciphers: same as TLS ciphers with added non AE ciphers
158 and Camellia
159 • key exchange: ECDHE, DHE (no DHE-DSS, no RSA)
161 • DH params size: >= 3072
163 • RSA keys size: >= 3072
165 • TLS protocols: TLS >= 1.2, DTLS >= 1.2
167 FIPS
169 A policy to aid conformance to the FIPS 140-2 requirements. This
170 policy is used internally by the fips-mode-setup(8) tool which can
171 switch the system into the FIPS 140-2 mode. This policy provides at
172 least 112-bit security.
173 • MACs: all HMAC with SHA1 or better
175 • Curves: all prime >= 256 bits
177 • Signature algorithms: with SHA-256 hash or better (no DSA)
179 • TLS Ciphers: >= 128-bit key, >= 128-bit block (AES, including
181 AES-CBC)
182 • non-TLS Ciphers: same as TLS Ciphers
184 • key exchange: ECDHE, DHE (no DHE-DSS, no RSA)
186 • DH params size: >= 2048
188 • RSA params size: >= 2048
190 • TLS protocols: TLS >= 1.2, DTLS >= 1.2
192 EMPTY
194 All cryptographic algorithms are disabled (used for debugging only,
195 do not use).
196
198 The crypto policy definition files have a simple syntax following an
199 INI file key = value syntax with these particular features:
200 • Comments are indicated by # character. Everything on the line
202 following the character is ignored.
203 • Backslash \ character followed immediately with the end-of-line
205 character indicates line continuation. The following line is
206 concatenated to the current line after the backslash and
207 end-of-line characters are removed.
208 • Value types for integer options can be decimal integers (option =
210 1).
211 • Multiple-choice options can be specified by setting them to a list
213 of values (option = value1 value2). This list can further be
214 altered by prepending/omitting/appending values (option = prepended
215 -omitted appended). A follow-up reassignment will reset the list.
216 The latter syntax cannot be combined with the former one in the
217 same directive. Setting an option to an empty list is possible with
218 option =.
219 • Asterisk sign can be used for wildcard matching as a shortcut for
221 specifying multiple values when setting multiple-choice options.
222 Note that wildcard matching can lead to future updates implicitly
223 enabling algorithms not yet available in the current version. If
224 this is a concern, do not use wildcard-matching outside of
225 algorithm-omitting directives.
226 • In order to limit the scope of the directive and make it affect
228 just some of the backends, the following extended syntax can be
229 used: option@scope = ..., option@{scope1,scope2,...} = ....
230 Negation of scopes is possible with option@!scope /
231 'option@{scope1,scope2,...}. Scope selectors are case-insensitive.
232 The available options are:
234 • mac: List of allowed MAC algorithms
236 • group: List of allowed groups or elliptic curves for key exchanges
238 for use with other protocols
239 • hash: List of allowed cryptographic hash (message digest)
241 algorithms
242 • sign: List of allowed signature algorithms
244 • cipher: List of allowed symmetric encryption algorithms (including
246 the modes) for use with other protocols
247 • key_exchange: List of allowed key exchange algorithms
249 • protocol: List of allowed TLS, DTLS and IKE protocol versions; mind
251 that some backends do not allow selectively disabling protocols
252 versions and only use the oldest version as the lower boundary.
253 • min_dh_size: Integer value of minimum number of bits of parameters
255 for DH key exchange
256 • min_dsa_size: Integer value of minimum number of bits for DSA keys
258 • min_rsa_size: Integer value of minimum number of bits for RSA keys
260 • sha1_in_certs: Value of 1 if SHA1 allowed in certificate
262 signatures, 0 otherwise (Applies to GnuTLS back end only.)
263 • arbitrary_dh_groups: Value of 1 if arbitrary group in
265 Diffie-Hellman is allowed, 0 otherwise
266 • ssh_certs: Value of 1 if OpenSSH certificate authentication is
268 allowed, 0 otherwise
269 • ssh_etm: Value of 1 if OpenSSH EtM (encrypt-then-mac) extension is
271 allowed, 0 otherwise
272 Full policy definition files have suffix .pol, subpolicy files have
274 suffix .pmod. Subpolicies do not have to have values set for all the
275 keys listed above.
276 The effective configuration of a policy with subpolicies applied is the
278 same as a configuration from a single policy obtained by concatenating
279 the policy and the subpolicies in question.
280 Policy file placement and naming:
282 The policy files shipped in packages are placed in
284 /usr/share/crypto-policies/policies and the subpolicies in
285 /usr/share/crypto-policies/policies/modules.
286 Locally configured policy files should be placed in
288 /etc/crypto-policies/policies and subpolicies in
289 /etc/crypto-policies/policies/modules.
290 The policy and subpolicy files must have names in upper-case except for
292 the .pol and .pmod suffix as the update-crypto-policies command always
293 converts the policy name to upper-case before searching for the policy
294 on the filesystem.
295
297 update-crypto-policies(8)
298 This command manages the policies available to the various
299 cryptographic back ends and allows the system administrator to
300 change the active cryptographic policy.
301 fips-mode-setup(8)
303 This command allows the system administrator to enable, or disable
304 the system FIPS mode and also apply the FIPS cryptographic policy
305 which limits the allowed algorithms and protocols to these allowed
306 by the FIPS 140-2 requirements.
307
309 Known notable exceptions
310 • Go-language applications do not yet follow the system-wide policy.
312 • GnuPG-2 application does not follow the system-wide policy.
314 In general only the data-in-transit is currently covered by the
316 system-wide policy.
317 If the system administrator changes the system-wide policy with the
319 update-crypto-policies(8) command it is advisable to restart the system
320 as the individual back-end libraries read the configuration files
321 usually during their initialization. The changes in the policy thus
322 take place in most cases only when the applications using the back-end
323 libraries are restarted.
324 Removed cipher suites and protocols
326 The following cipher suites and protocols are completely removed from
328 the core cryptographic libraries listed above:
329 • DES
331 • All export grade cipher suites
333 • MD5 in signatures
335 • SSLv2
337 • SSLv3
339 • All ECC curves smaller than 224 bits
341 • All binary field ECC curves
343 Cipher suites and protocols disabled in all predefined policies
345 The following ciphersuites and protocols are available but disabled in
347 all predefined crypto policies:
348 • DH with parameters < 1024 bits
350 • RSA with key size < 1024 bits
352 • Camellia
354 • RC4
356 • ARIA
358 • SEED
360 • IDEA
362 • Integrity only ciphersuites
364 • TLS CBC mode ciphersuites using SHA-384 HMAC
366 • AES-CCM8
368 • all ECC curves incompatible with TLS 1.3, including secp256k1
370 • IKEv1
372 Notable irregularities in the individual configuration generators
374 • OpenSSL and NSS: Disabling all TLS and/or all DTLS versions isn’t
376 actually possible. Trying to do so will result in the library
377 defaults being applied instead.
378 • OpenSSL: The minimum length of the keys and some other parameters
380 are enforced by the @SECLEVEL value which does not provide a fine
381 granularity. The list of TLS ciphers is not generated as an exact
382 list but by subtracting from all the supported ciphers for the
383 enabled key exchange methods. For that reason there is no way to
384 disable a random cipher. In particular all AES-128 ciphers are
385 disabled if the AES-128-GCM is not present in the list; all AES-256
386 ciphers are disabled if the AES-256-GCM is not present. The CBC
387 ciphers are disabled if there isn’t HMAC-SHA1 in the hmac list and
388 AES-256-CBC in the cipher list. To disable the CCM ciphers both
389 AES-128-CCM and AES-256-CCM must not be present in the cipher list.
390 • GnuTLS: The minimum length of the keys and some other parameters
392 are enforced by min-verification-profile setting in the GnuTLS
393 configuration file which does not provide fine granularity.
394 • GnuTLS: PSK key exchanges have to be explicitly enabled by the
396 applications using them.
397 • GnuTLS: HMAC-SHA2-256 and HMAC-SHA2-384 MACs are disabled due to
399 concerns over the constant-timedness of the implementation.
400 • OpenSSH: DH group 1 is always disabled on server even if the policy
402 allows 1024 bit DH groups in general. The OpenSSH configuration
403 option HostKeyAlgorithms is set only for the SSH server as
404 otherwise the handling of the existing known hosts entries would be
405 broken on client.
406 • Libreswan: The key_exchange parameter does not affect the generated
408 configuration. The use of regular DH or ECDH can be limited with
409 appropriate setting of the group parameter.
410
412 The ECDHE-GSS and DHE-GSS algorithms are newly introduced and must be
413 specified in the base policy for the SSH GSSAPI key exchange methods to
414 be enabled. Previously the legacy SSH GSSAPI key exchange methods were
415 automatically enabled when the SHA1 hash and DH parameters of at least
416 2048 bits were enabled.
417 Before the introduction of the custom crypto policies support it was
419 possible to have an completely arbitrary crypto policy created as a set
420 of arbitrary back-end config files in
421 /usr/share/crypto-policies/<POLICYNAME> directory. With the
422 introduction of the custom crypto policies it is still possible but
423 there must be an empty (possibly with any comment lines)
424 <POLICYNAME>.pol file in /usr/share/crypto-policies/policies so the
425 update-crypto-policies command can recognize the arbitrary custom
426 policy. No subpolicies must be used with such an arbitrary custom
427 policy. Modifications from local.d will be appended to the files
428 provided by the policy.
429 The use of the following historaically available options is
431 discouraged:
432 • min_tls_version: Lowest allowed TLS protocol version (recommended
434 replacement: protocol@TLS)
435 • min_dtls_version: Lowest allowed DTLS protocol version (recommended
437 replacement: protocol@TLS)
438 The following options are deprecated, please rewrite your policies:
440 • ike_protocol: List of allowed IKE protocol versions (recommended
442 replacement: protocol@IKE, mind the relative position to other
443 protocol directives).
444 • tls_cipher: list of allowed symmetric encryption algorithms for use
446 with the TLS protocol (recommended replacement: cipher@TLS, mind
447 the relative position to other cipher directives).
448 • ssh_cipher: list of allowed symmetric encryption algorithms for use
450 with the SSH protocol (recommended replacement: cipher@SSH, mind
451 the relative position to other cipher directives).
452 • ssh_group: list of allowed groups or elliptic curves for key
454 exchanges for use with the SSH protocol (recommended replacement:
455 group@SSH, mind the relative position to other group directives).
456 • sha1_in_dnssec: Allow SHA1 usage in DNSSec protocol even if it is
458 not present in the hash and sign lists (recommended replacements:
459 hash@DNSSec, sign@DNSSec).
460
462 /etc/crypto-policies/back-ends
463 The individual cryptographical back-end configuration files.
464 Usually linked to the configuration shipped in the crypto-policies
465 package unless a configuration from local.d is added.
466 /etc/crypto-policies/config
468 A file containing the name of the active crypto-policy set on the
469 system.
470 /etc/crypto-policies/local.d
472 Additional configuration shipped by other packages or created by
473 the system administrator. The contents of the
474 <back-end>-file.config is appended to the configuration from the
475 policy back end as shipped in the crypto-policies package.
476 /usr/share/crypto-policies/policies
478 System policy definition files.
479 /usr/share/crypto-policies/policies/modules
481 System subpolicy definition files.
482 /etc/crypto-policies/policies
484 Custom policy definition files as configured by the system
485 administrator.
486 /etc/crypto-policies/policies/modules
488 Custom subpolicy definition files as configured by the system
489 administrator.
490 /usr/share/crypto-policies/<'POLICYNAME'>
492 Pre-generated back-end configurations for policy POLICYNAME.
493
495 update-crypto-policies(8), fips-mode-setup(8)
496
498 Written by Tomáš Mráz.
499crypto-policies 08/15/2022 CRYPTO-POLICIES(7)