1CRYPTO-POLICIES(7) CRYPTO-POLICIES(7)
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6 crypto-policies - system-wide crypto policies overview
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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.
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16 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.
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21 The individual policy levels (DEFAULT, LEGACY, FUTURE, and FIPS) are
22 included in the crypto-policies(7) package. In the future, there will
23 be also a mechanism for easy creation and deployment of policies
24 defined by the system administrator or a third party vendor.
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26 For rationale, see RFC 7457 for a list of attacks taking advantage of
27 legacy crypto algorithms.
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30 Crypto-policies apply to the configuration of the core cryptographic
31 subsystems, covering TLS, IKE, IPSec, DNSSec, and Kerberos protocols;
32 i.e., the supported secure communications protocols on the base
33 operating system.
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35 Once an application runs in the operating system, it follows the
36 default or selected policy and refuses to fall back to algorithms and
37 protocols not within the policy, unless the user has explicitly
38 requested the application to do so. That is, the policy applies to the
39 default behavior of applications when running with the system-provided
40 configuration but the user can override it on an application-specific
41 basis.
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43 The policies currently provide settings for these applications and
44 libraries:
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46 · BIND DNS name server daemon
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48 · GnuTLS TLS library
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50 · OpenJDK runtime environment
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52 · Kerberos 5 library
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54 · Libreswan IPsec and IKE protocol implementation
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56 · NSS TLS library
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58 · OpenSSH SSH2 protocol implementation
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60 · OpenSSL TLS library
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62 · libssh SSH2 protocol implementation
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64 Applications using the above libraries and tools are covered by the
65 cryptographic policies unless they are explicitly configured not to be
66 so.
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69 LEGACY
70 This policy ensures maximum compatibility with legacy systems; it
71 is less secure and it includes support for TLS 1.0, TLS 1.1, and
72 SSH2 protocols or later. The algorithms DSA, 3DES, and RC4 are
73 allowed, while RSA and Diffie-Hellman parameters are accepted if
74 larger than 1023 bits. The level provides at least 64-bit security.
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76 · MACs: all HMAC with SHA-1 or better + all modern MACs (Poly1305
77 etc.)
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79 · Curves: all prime >= 255 bits (including Bernstein curves)
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81 · Signature algorithms: with SHA1 hash or better (DSA allowed)
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83 · TLS Ciphers: all available >= 112-bit key, >= 128-bit block
84 (including RC4 and 3DES)
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86 · Non-TLS Ciphers: same as TLS ciphers with added Camellia
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88 · Key exchange: ECDHE, RSA, DHE
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90 · DH params size: >= 1023
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92 · RSA keys size: >= 1023
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94 · DSA params size: >= 1023
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96 · TLS protocols: TLS >= 1.0, DTLS >= 1.0
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98 DEFAULT
99 The DEFAULT policy is a reasonable default policy for today’s
100 standards. It allows the TLS 1.0, TLS 1.1, TLS 1.2, and TLS 1.3
101 protocols, as well as IKEv2 and SSH2. The Diffie-Hellman parameters
102 are accepted if they are at least 1023 bits long. The level
103 provides at least 80-bit security.
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105 · MACs: all HMAC with SHA-1 or better + all modern MACs (Poly1305
106 etc.)
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108 · Curves: all prime >= 255 bits (including Bernstein curves)
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110 · Signature algorithms: with SHA-1 hash or better (no DSA)
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112 · TLS Ciphers: >= 128-bit key, >= 128-bit block (AES, ChaCha20,
113 including AES-CBC)
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115 · non-TLS Ciphers: as TLS Ciphers with added Camellia
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117 · key exchange: ECDHE, RSA, DHE (no DHE-DSS)
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119 · DH params size: >= 1023
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121 · RSA keys size: >= 2048
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123 · TLS protocols: TLS >= 1.0, DTLS >= 1.0
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125 NEXT
126 The NEXT policy is a policy prepared for the upcoming release of
127 the operating system so it can be easily tested. It allows the TLS
128 1.2 and TLS 1.3 protocols, as well as IKEv2 and SSH2. The RSA and
129 Diffie-Hellman parameters are accepted if larger than 2047 bits.
130 The level provides at least 112-bit security with the exception of
131 SHA-1 signatures needed for DNSSec and other still prevalent legacy
132 use of SHA-1 signatures.
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134 · MACs: all HMAC with SHA-1 or better + all modern MACs (Poly1305
135 etc.)
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137 · Curves: all prime >= 255 bits (including Bernstein curves)
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139 · Signature algorithms: with SHA-1 hash or better (no DSA)
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141 · TLS Ciphers: >= 128-bit key, >= 128-bit block (AES, ChaCha20,
142 including AES-CBC)
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144 · non-TLS Ciphers: as TLS Ciphers with added Camellia
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146 · key exchange: ECDHE, RSA, DHE (no DHE-DSS)
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148 · DH params size: >= 2048
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150 · RSA keys size: >= 2048
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152 · TLS protocols: TLS >= 1.2, DTLS >= 1.2
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154 FUTURE
155 A conservative security level that is believed to withstand any
156 near-term future attacks. This level does not allow the use of
157 SHA-1 in signature algorithms. The level also provides some (not
158 complete) preparation for post-quantum encryption support in form
159 of 256-bit symmetric encryption requirement. The RSA and
160 Diffie-Hellman parameters are accepted if larger than 3071 bits.
161 The level provides at least 128-bit security.
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163 · MACs: all HMAC with SHA-256 or better + all modern MACs
164 (Poly1305 etc.)
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166 · Curves: all prime >= 255 bits (including Bernstein curves)
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168 · Signature algorithms: with SHA-256 hash or better (no DSA)
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170 · TLS Ciphers: >= 256-bit key, >= 128-bit block, only
171 Authenticated Encryption (AE) ciphers
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173 · non-TLS Ciphers: same as TLS ciphers with added non AE ciphers
174 and Camellia
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176 · key exchange: ECDHE, DHE (no DHE-DSS, no RSA)
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178 · DH params size: >= 3072
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180 · RSA keys size: >= 3072
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182 · TLS protocols: TLS >= 1.2, DTLS >= 1.2
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184 FIPS
185 A level that conforms to the FIPS 140-2 requirements. This policy
186 is used internally by the fips-mode-setup(8) tool which can switch
187 the system into the FIPS 140-2 compliance mode. The level provides
188 at least 112-bit security.
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190 · MACs: all HMAC with SHA1 or better
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192 · Curves: all prime >= 256 bits
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194 · Signature algorithms: with SHA-256 hash or better (no DSA)
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196 · TLS Ciphers: >= 128-bit key, >= 128-bit block (AES, including
197 AES-CBC)
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199 · non-TLS Ciphers: same as TLS Ciphers
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201 · key exchange: ECDHE, DHE (no DHE-DSS, no RSA)
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203 · DH params size: >= 2048
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205 · RSA params size: >= 2048
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207 · TLS protocols: TLS >= 1.2, DTLS >= 1.2
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209 EMPTY
210 All cryptographic algorithms are disabled (used for debugging only,
211 do not use).
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214 The crypto policy definiton files have a simple syntax following an INI
215 file key = value syntax with these particular features:
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217 · Comments are indicated by # character. Everything on the line
218 following the character is ignored.
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220 · Backslash \ character followed immediately with the end-of-line
221 character indicates line continuation. The following line is
222 concatenated to the current line after the backslash and
223 end-of-line characters are removed.
224
225 · Value types can be either decimal integers, arbitrary strings, or
226 lists of strings without whitespace characters separated by any
227 number of whitespaces.
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229 The allowed keys are:
230
231 · mac: List of allowed MAC algorithms
232
233 · ssh_group: Optional; list of allowed groups or elliptic curves for
234 key exchanges for use with the SSH protocol. If absent, the value
235 is derived from group.
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237 · group: List of allowed groups or elliptic curves for key exchanges
238 for use with other protocols
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240 · hash: List of allowed cryptographic hash (message digest)
241 algorithms
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243 · sign: List of allowed signature algorithms
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245 · tls_cipher: Optional; list of allowed symmetric encryption
246 algorithms (including the modes) for use with the TLS protocol. If
247 absent, the value is derived from cipher.
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249 · ssh_cipher: Optional; list of allowed symmetric encryption
250 algorithms (including the modes) for use with the SSH protocol. If
251 absent, the value is derived from cipher.
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253 · cipher: List of allowed symmetric encryption algorithms (including
254 the modes) for use with other protocols
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256 · key_exchange: List of allowed key exchange algorithms
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258 · protocol: List of allowed TLS and DTLS protocol versions (ignored
259 by OpenSSL and NSS back ends)
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261 · ike_protocol: List of allowed IKE protocol versions
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263 · min_tls_version: Lowest allowed TLS protocol version (used only by
264 OpenSSL a and NSS back ends)
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266 · min_dtls_version: Lowest allowed DTLS protocol version (used only
267 by NSS back end)
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269 · min_dh_size: Integer value of minimum number of bits of parameters
270 for DH key exchange
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272 · min_dsa_size: Integer value of minimum number of bits for DSA keys
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274 · min_rsa_size: Integer value of minimum number of bits for RSA keys
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276 · sha1_in_certs: Value of 1 if SHA1 allowed in certificate
277 signatures, 0 otherwise (Applies to GnuTLS back end only.)
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279 · arbitrary_dh_groups: Value of 1 if arbitrary group in
280 Diffie-Hellman is allowed, 0 otherwise
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282 · ssh_certs: Value of 1 if OpenSSH certificate authentication is
283 allowed, 0 otherwise
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285 · ssh_etm: Value of 1 if OpenSSH EtM (encrypt-then-mac) extension is
286 allowed, 0 otherwise
287
288 The full policy definition files have suffix .pol, the policy module
289 definition files have suffix .pmod. The policy module files do not have
290 to have values set for all the keys listed above.
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292 The lists as set in the base (full policy) are modified by the lists
293 specified in the module files in following way:
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295 · -list-item: The list-item is removed from the list specified in the
296 base policy.
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298 · +list-item: The list-item is inserted at the beginning of the list
299 specified in the base policy. The inserts are done in the order of
300 appearance in the policy module file so the actual order in the
301 final list will be reversed.
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303 · list-item or list-item+: The list-item is appended to the end of
304 the list specified in the base policy.
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306 Non-list key values in the policy module files are simply overriden.
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308 The keys marked as Optional can be omitted in the policy definition
309 files. In that case, the values will be derived from the base keys.
310 Note that, this value propagation only applies to the policy definition
311 files. In the policy module files, each key that needs modification
312 must be explicitly specified.
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315 update-crypto-policies(8)
316 This command manages the policies available to the various
317 cryptographic back ends and allows the system administrator to
318 change the active cryptographic policy level.
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320 fips-mode-setup(8)
321 This command allows the system administrator to enable, or disable
322 the system FIPS mode and also apply the FIPS cryptographic policy
323 level which limits the allowed algorithms and protocols to these
324 allowed by the FIPS 140-2 requirements.
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327 Exceptions:
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329 · Go-language applications do not yet follow the system-wide policy.
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331 · GnuPG-2 application does not follow the system-wide policy.
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333 In general only the data-in-transit is currently covered by the
334 system-wide policy.
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336 If the system administrator changes the system-wide policy level with
337 the update-crypto-policies(8) command it is advisable to restart the
338 system as the individual back-end libraries read the configuration
339 files usually during their initialization. The changes in the policy
340 level thus take place in most cases only when the applications using
341 the back-end libraries are restarted.
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343 Removed cipher suites and protocols
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345 The following cipher suites and protocols are completely removed from
346 the core cryptographic libraries listed above:
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348 · DES
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350 · All export grade cipher suites
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352 · MD5 in signatures
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354 · SSLv2
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356 · SSLv3
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358 · All ECC curves smaller than 224 bits
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360 · All binary field ECC curves
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362 Cipher suites and protocols disabled in all policy levels
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364 The following ciphersuites and protocols are available but disabled in
365 all crypto policy levels. They can be enabled only by explicit
366 configuration of individual applications:
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368 · DH with parameters < 1024 bits
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370 · RSA with key size < 1024 bits
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372 · Camellia
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374 · ARIA
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376 · SEED
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378 · IDEA
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380 · Integrity only ciphersuites
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382 · TLS CBC mode ciphersuites using SHA-384 HMAC
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384 · AES-CCM8
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386 · all ECC curves incompatible with TLS 1.3, including secp256k1
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388 · IKEv1
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391 /etc/crypto-policies/back-ends
392 The individual cryptographical back-end configuration files.
393 Usually linked to the configuration shipped in the crypto-policies
394 package unless a configuration from local.d is added.
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396 /etc/crypto-policies/config
397 The active crypto-policies level set on the system.
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399 /etc/crypto-policies/local.d
400 Additional configuration shipped by other packages or created by
401 the system administrator. The contents of the
402 <back-end>-file.config is appended to the configuration from the
403 policy back end as shipped in the crypto-policies package.
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406 update-crypto-policies(8), fips-mode-setup(8)
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409 Written by Tomáš Mráz.
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413crypto-policies 12/16/2019 CRYPTO-POLICIES(7)