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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Nir 3 Internet-Draft Check Point 4 Obsoletes: 4307 (if approved) T. Kivinen 5 Updates: 7296 (if approved) INSIDE Secure 6 Intended status: Standards Track P. Wouters 7 Expires: November 12, 2016 Red Hat 8 D. Migault 9 Ericsson 10 May 11, 2016 12 Algorithm Implementation Requirements and Usage Guidance for IKEv2 13 draft-ietf-ipsecme-rfc4307bis-08 15 Abstract 17 The IPsec series of protocols makes use of various cryptographic 18 algorithms in order to provide security services. The Internet Key 19 Exchange (IKE) protocol is used to negotiate the IPsec Security 20 Association (IPsec SA) parameters, such as which algorithms should be 21 used. To ensure interoperability between different implementations, 22 it is necessary to specify a set of algorithm implementation 23 requirements and usage guidance to ensure that there is at least one 24 algorithm that all implementations support. This document defines 25 the current algorithm implementation requirements and usage guidance 26 for IKEv2. This document does not update the algorithms used for 27 packet encryption using IPsec Encapsulated Security Payload (ESP). 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on November 12, 2016. 46 Copyright Notice 48 Copyright (c) 2016 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 1.1. Updating Algorithm Implementation Requirements and Usage 65 Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 3 67 1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 4 68 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 69 3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5 70 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5 71 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 6 72 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 7 73 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 8 74 4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 10 75 4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 10 76 4.1.1. Recommendations for RSA key length . . . . . . . . . 11 77 4.2. Digital Signature Recommendations . . . . . . . . . . . . 11 78 5. Algorithms for Internet of Things . . . . . . . . . . . . . . 12 79 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 80 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 81 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 82 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 83 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 84 9.2. Informative References . . . . . . . . . . . . . . . . . 14 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 87 1. Introduction 89 The Internet Key Exchange (IKE) protocol [RFC7296] is used to 90 negotiate the parameters of the IPsec SA, such as the encryption and 91 authentication algorithms and the keys for the protected 92 communications between the two endpoints. The IKE protocol itself is 93 also protected by cryptographic algorithms which are negotiated 94 between the two endpoints using IKE. Different implementations of 95 IKE may negotiate different algorithms based on their individual 96 local policy. To ensure interoperability, a set of "mandatory-to- 97 implement" IKE cryptographic algorithms is defined. 99 This document describes the parameters of the IKE protocol and 100 updates the IKEv2 specification because it changes the mandatory to 101 implement authentication algorithms of the section 4 of the RFC7296 102 by saying RSA key lengths of less than 2048 are SHOULD NOT. It does 103 not describe the cryptographic parameters of the AH or ESP protocols. 105 1.1. Updating Algorithm Implementation Requirements and Usage Guidance 107 The field of cryptography evolves continuously. New stronger 108 algorithms appear and existing algorithms are found to be less secure 109 then originally thought. Therefore, algorithm implementation 110 requirements and usage guidance need to be updated from time to time 111 to reflect the new reality. The choices for algorithms must be 112 conservative to minimize the risk of algorithm compromise. 113 Algorithms need to be suitable for a wide variety of CPU 114 architectures and device deployments ranging from high end bulk 115 encryption devices to small low-power IoT devices. 117 The algorithm implementation requirements and usage guidance may need 118 to change over time to adapt to the changing world. For this reason, 119 the selection of mandatory-to-implement algorithms was removed from 120 the main IKEv2 specification and placed in a separate document. 122 1.2. Updating Algorithm Requirement Levels 124 The mandatory-to-implement algorithm of tomorrow should already be 125 available in most implementations of IKE by the time it is made 126 mandatory. This document attempts to identify and introduce those 127 algorithms for future mandatory-to-implement status. There is no 128 guarantee that the algorithms in use today may become mandatory in 129 the future. Published algorithms are continuously subjected to 130 cryptographic attack and may become too weak or could become 131 completely broken before this document is updated. 133 This document only provides recommendations for the mandatory-to- 134 implement algorithms or algorithms too weak that are recommended not 135 to be implemented. As a result, any algorithm listed at the IKEv2 136 IANA registry not mentioned in this document MAY be implemented. For 137 clarification and consistency with [RFC4307] an algorithm will be 138 denoted here as MAY only when it has been downgraded. 140 Although this document updates the algorithms to keep the IKEv2 141 communication secure over time, it also aims at providing 142 recommendations so that IKEv2 implementations remain interoperable. 143 IKEv2 interoperability is addressed by an incremental introduction or 144 deprecation of algorithms. In addition, this document also considers 145 the new use cases for IKEv2 deployment, such as Internet of Things 146 (IoT). 148 It is expected that deprecation of an algorithm is performed 149 gradually. This provides time for various implementations to update 150 their implemented algorithms while remaining interoperable. Unless 151 there are strong security reasons, an algorithm is expected to be 152 downgraded from MUST to MUST- or SHOULD, instead of MUST NOT. 153 Similarly, an algorithm that has not been mentioned as mandatory-to- 154 implement is expected to be introduced with a SHOULD instead of a 155 MUST. 157 The current trend toward Internet of Things and its adoption of IKEv2 158 requires this specific use case to be taken into account as well. 159 IoT devices are resource constrained devices and their choice of 160 algorithms are motivated by minimizing the footprint of the code, the 161 computation effort and the size of the messages to send. This 162 document indicates "[IoT]" when a specified algorithm is specifically 163 listed for IoT devices. Requirement levels that are marked as "IoT" 164 apply to IoT devices and to server-side implementations that might 165 presumably need to interoperate with them, including any general- 166 purpose VPN gateways. 168 1.3. Document Audience 170 The recommendations of this document mostly target IKEv2 implementers 171 as implementations need to meet both high security expectations as 172 well as high interoperability between various vendors and with 173 different versions. Interoperability requires a smooth move to more 174 secure cipher suites. This may differ from a user point of view that 175 may deploy and configure IKEv2 with only the safest cipher suite. On 176 the other hand, comments from this document are also expected to be 177 useful for such users. 179 IKEv1 is out of scope of this document. IKEv1 is deprecated and the 180 recommendations of this document must not be considered for IKEv1, as 181 most IKEv1 implementations have been "frozen" and will not be able to 182 update the list of mandatory-to-implement algorithms. 184 2. Conventions Used in This Document 186 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 187 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 188 document are to be interpreted as described in [RFC2119]. 190 We define some additional terms here: 192 SHOULD+ This term means the same as SHOULD. However, it is likely 193 that an algorithm marked as SHOULD+ will be promoted at 194 some future time to be a MUST. 195 SHOULD- This term means the same as SHOULD. However, an algorithm 196 marked as SHOULD- may be deprecated to a MAY in a future 197 version of this document. 198 MUST- This term means the same as MUST. However, we expect at 199 some point that this algorithm will no longer be a MUST in 200 a future document. Although its status will be determined 201 at a later time, it is reasonable to expect that if a 202 future revision of a document alters the status of a MUST- 203 algorithm, it will remain at least a SHOULD or a SHOULD- 204 level. 205 IoT stands for Internet of Things. 207 3. Algorithm Selection 209 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms 211 The algorithms in the below table are negotiated in the SA payload 212 and used for the Encrypted Payload. References to the specification 213 defining these algorithms and the ones in the following subsections 214 are in the IANA registry [IKEV2-IANA]. Some of these algorithms are 215 Authenticated Encryption with Associated Data (AEAD - [RFC5282]). 216 Algorithms that are not AEAD MUST be used in conjunction with an 217 integrity algorithms in Section 3.3. 219 +-----------------------------+----------+-------+----------+ 220 | Name | Status | AEAD? | Comment | 221 +-----------------------------+----------+-------+----------+ 222 | ENCR_AES_CBC | MUST- | No | [1] | 223 | ENCR_CHACHA20_POLY1305 | SHOULD | Yes | | 224 | AES-GCM with a 16 octet ICV | SHOULD | Yes | [1] | 225 | ENCR_AES_CCM_8 | SHOULD | Yes | [1][IoT] | 226 | ENCR_3DES | MAY | No | | 227 | ENCR_DES | MUST NOT | No | | 228 +-----------------------------+----------+-------+----------+ 230 [1] - This requirement level is for 128-bit keys. 256-bit keys are at 231 SHOULD. 192-bit keys can safely be ignored. [IoT] - This requirement 232 is for interoperability with IoT. 234 ENCR_AES_CBC is raised from SHOULD+ in [RFC4307] to MUST. It is the 235 only shared mandatory-to-implement algorithm with RFC4307 and as a 236 result it is necessary for interoperability with IKEv2 implementation 237 compatible with RFC4307. 239 ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of 240 RFC4307. It has been recommended by the CRFG and others as an 241 alternative to AES-CBC and AES-GCM. It is also being standardized 242 for IPsec for the same reasons. At the time of writing, there were 243 not enough IKEv2 implementations supporting ENCR_CHACHA20_POLY1305 to 244 be able to introduce it at the SHOULD+ level. 246 AES-GCM with a 16 octet ICV was not considered in RFC4307. At the 247 time RFC4307 was written, AES-GCM was not defined in an IETF 248 document. AES-GCM was defined for ESP in [RFC4106] and later for 249 IKEv2 in [RFC5282]. The main motivation for adopting AES-GCM for ESP 250 is encryption performance and key longevity compared to AES-CBC. 251 This resulted in AES-GCM being widely implemented for ESP. As the 252 computation load of IKEv2 is relatively small compared to ESP, many 253 IKEv2 implementations have not implemented AES-GCM. For this reason, 254 AES-GCM is not promoted to a greater status than SHOULD. The reason 255 for promotion from MAY to SHOULD is to promote the slightly more 256 secure AEAD method over the traditional encrypt+auth method. Its 257 status is expected to be raised once widely implemented. As the 258 advantage of the shorter (and weaker) ICVs is minimal, the 8 and 12 259 octet ICV's remain at the MAY level. 261 ENCR_AES_CCM_8 was not considered in RFC4307. This document 262 considers it as SHOULD be implemented in order to be able to interact 263 with Internet of Things devices. As this case is not a general use 264 case for non-IoT VPNs, its status is expected to remain as SHOULD. 265 The 8 octet size of the ICV is expected to be sufficient for most use 266 cases of IKEv2, as far less packets are exchanged on those cases, and 267 IoT devices want to make packets as small as possible. When 268 implemented, ENCR_AES_CCM_8 MUST be implemented for key length 128 269 and MAY be implemented for key length 256. 271 ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All 272 IKEv2 implementation already implement ENCR_AES_CBC, so there is no 273 need to keep support for the much slower ENCR_3DES. In addition, 274 ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES. 276 ENCR_DES can be brute-forced using of-the-shelves hardware. It 277 provides no meaningful security whatsoever and therefor MUST NOT be 278 implemented. 280 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms 282 Transform Type 2 algorithms are pseudo-random functions used to 283 generate pseudo-random values when needed. 285 If an algorithm is selected as the integrity algorithm, it SHOULD 286 also be used as the PRF. When using an AEAD cipher, a choice of PRF 287 needs to be made. The table below lists the recommended algorithms. 289 +-------------------+----------+---------+ 290 | Name | Status | Comment | 291 +-------------------+----------+---------+ 292 | PRF_HMAC_SHA2_256 | MUST | | 293 | PRF_HMAC_SHA2_512 | SHOULD+ | | 294 | PRF_HMAC_SHA1 | MUST- | | 295 | PRF_AES128_XCBC | SHOULD | [IoT] | 296 | PRF_HMAC_MD5 | MUST NOT | | 297 +-------------------+----------+---------+ 299 [IoT] - This requirement is for interoperability with IoT 301 PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based 302 transforms were mentioned. PRF_HMAC_SHA2_256 MUST be implemented in 303 order to replace SHA1 and PRF_HMAC_SHA1. 305 PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for 306 PRF_HMAC_SHA2_256 or when stronger security is required. 307 PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the 308 additional overhead of PRF_HMAC_SHA2_512 is negligible. 310 PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as 311 their is an industry-wide trend to deprecate its usage. 313 PRF_AES128_XCBC is only recommended in the scope of IoT, as Internet 314 of Things deployments tend to prefer AES based pseudo-random 315 functions in order to avoid implementing SHA2. For the non-IoT VPN 316 deployment it has been downgraded from SHOULD in RFC4307 to MAY as it 317 has not seen wide adoption. 319 PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT. 320 There is an industry-wide trend to deprecate its usage as MD5 support 321 is being removed from cryptographic libraries in general because its 322 non-HMAC use is known to be subject to collision attacks, for example 323 as mentioned in [TRANSCRIPTION]. 325 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms 327 The algorithms in the below table are negotiated in the SA payload 328 and used for the Encrypted Payload. References to the specification 329 defining these algorithms are in the IANA registry. When an AEAD 330 algorithm (see Section 3.1) is proposed, this algorithm transform 331 type is not in use. 333 +------------------------+----------+---------+ 334 | Name | Status | Comment | 335 +------------------------+----------+---------+ 336 | AUTH_HMAC_SHA2_256_128 | MUST | | 337 | AUTH_HMAC_SHA2_512_256 | SHOULD | | 338 | AUTH_HMAC_SHA1_96 | MUST- | | 339 | AUTH_AES_XCBC_96 | SHOULD | [IoT] | 340 | AUTH_HMAC_MD5_96 | MUST NOT | | 341 | AUTH_DES_MAC | MUST NOT | | 342 | AUTH_KPDK_MD5 | MUST NOT | | 343 +------------------------+----------+---------+ 345 [IoT] - This requirement is for interoperability with IoT 347 AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based 348 transforms were mentioned. AUTH_HMAC_SHA2_256_128 MUST be 349 implemented in order to replace AUTH_HMAC_SHA1_96. 351 AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement 352 of AUTH_HMAC_SHA2_256_128 or when stronger security is required. 353 This value has been preferred over AUTH_HMAC_SHA2_384, as the 354 additional overhead of AUTH_HMAC_SHA2_512 is negligible. 356 AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST- 357 as there is an industry-wide trend to deprecate its usage. 359 AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of 360 Things deployments tend to prefer AES based pseudo-random functions 361 in order to avoid implementing SHA2. For the non-IoT VPN deployment, 362 it has been downgraded from SHOULD in RFC4307 to MAY as it has not 363 been widely adopted. 365 AUTH_DES_MAC, AUTH_HMAC_MD5_96, and AUTH_KPDK_MD5 were not mentioned 366 in RFC4307 so their default status ware MAY. They have been 367 downgraded to MUST NOT. There is an industry-wide trend to deprecate 368 DES and MD5. MD5 support is being removed from cryptographic 369 libraries in general because its non-HMAC use is known to be subject 370 to collision attacks, for example as mentioned in [TRANSCRIPTION]. 372 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 374 There are several Modular Exponential (MODP) groups and several 375 Elliptic Curve groups (ECC) that are defined for use in IKEv2. These 376 groups are defined in both the [IKEv2] base document and in 377 extensions documents and are identified by group number. Note that 378 it is critical to enforce a secure Diffie-Hellman exchange as this 379 exchange provides keys for the session. If an attacker can retrieve 380 the private numbers (a, or b) and the public values (g**a, and g**b), 381 then the attacker can compute the secret and the keys used and 382 decrypt the exchange and IPsec SA created inside the IKEv2 SA. Such 383 an attack can be performed off-line on a previously recorded 384 communication, years after the communication happened. This differs 385 from attacks that need to be executed during the authentication which 386 must be performed online and in near real-time. 388 +--------+---------------------------------------------+------------+ 389 | Number | Description | Status | 390 +--------+---------------------------------------------+------------+ 391 | 14 | 2048-bit MODP Group | MUST | 392 | 19 | 256-bit random ECP group | SHOULD | 393 | 5 | 1536-bit MODP Group | SHOULD NOT | 394 | 2 | 1024-bit MODP Group | SHOULD NOT | 395 | 1 | 768-bit MODP Group | MUST NOT | 396 | 22 | 1024-bit MODP Group with 160-bit Prime | SHOULD NOT | 397 | | Order Subgroup | | 398 | 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT | 399 | | Order Subgroup | | 400 | 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT | 401 | | Order Subgroup | | 402 +--------+---------------------------------------------+------------+ 404 Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as 405 a replacement for 1024-bit MODP Group. Group 14 is widely 406 implemented and considered secure. 408 Group 19 or 256-bit random ECP group was not specified in RFC4307, as 409 this group were not specified at that time. Group 19 is widely 410 implemented and considered secure. 412 Group 5 or 1536-bit MODP Group has been downgraded from MAY in 413 RFC4307 to SHOULD NOT. It was specified earlier, but is now 414 considered to be vulnerable to be broken within the next few years by 415 a nation state level attack, so its security margin is considered too 416 narrow. 418 Group 2 or 1024-bit MODP Group has been downgraded from MUST- in 419 RFC4307 to SHOULD NOT. It is known to be weak against sufficiently 420 funded attackers using commercially available mass-computing 421 resources, so its security margin is considered too narrow. It is 422 expected in the near future to be downgraded to MUST NOT. 424 Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its 425 status was MAY. It can be broken within hours using cheap of-the- 426 shelves hardware. It provides no security whatsoever. 428 Group 22, 23 and 24 or 1024-bit MODP Group with 160-bit, and 2048-bit 429 MODP Group with 224-bit and 256-bit Prime Order Subgroup have small 430 subgroups, which means that checks specified in the "Additional 431 Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2 first bullet 432 point MUST be done when these groups are used. These groups are also 433 not safe-primes. The seeds for these groups have not been publicly 434 released, resulting in reduced trust in these groups. These groups 435 were proposed as alternatives for group 2 and 14 but never saw wide 436 deployment. It is expected in the near future to be further 437 downgraded to MUST NOT. 439 4. IKEv2 Authentication 441 IKEv2 authentication may involve a signatures verification. 442 Signatures may be used to validate a certificate or to check the 443 signature of the AUTH value. Cryptographic recommendations regarding 444 certificate validation are out of scope of this document. What is 445 mandatory to implement is provided by the PKIX Community. This 446 document is mostly concerned on signature verification and generation 447 for the authentication. 449 4.1. IKEv2 Authentication Method 451 +--------+---------------------------------------+------------+ 452 | Number | Description | Status | 453 +--------+---------------------------------------+------------+ 454 | 1 | RSA Digital Signature | MUST | 455 | 2 | Shared Key Message Integrity Code | MUST | 456 | 3 | DSS Digital Signature | SHOULD NOT | 457 | 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD | 458 | 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD | 459 | 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD | 460 | 14 | Digital Signature | SHOULD | 461 +--------+---------------------------------------+------------+ 463 RSA Digital Signature is widely deployed and therefore kept for 464 interoperability. It is expected to be downgraded in the future as 465 its signatures are based on the older RSASSA-PKCS1-v1.5 which is no 466 longer recommended. RSA authentication, as well as other specific 467 Authentication Methods, are expected to be replaced with the generic 468 Digital Signature method of [RFC7427]. RSA Digital Signature is not 469 recommended for keys smaller then 2048, but since these signatures 470 only have value in real-time, and need no future protection, smaller 471 keys was kept at SHOULD NOT instead of MUST NOT. 473 Shared Key Message Integrity Code is widely deployed and mandatory to 474 implement in the IKEv2 in the RFC7296. 476 ECDSA based Authentication Methods are also expected to be downgraded 477 as it does not provide hash function agility. Instead, ECDSA (like 478 RSA) is expected to be performed using the generic Digital Signature 479 method. 481 DSS Digital Signature is bound to SHA-1 and has the same level of 482 security as 1024-bit RSA. It is expected to be downgraded to MUST 483 NOT in the future. 485 Digital Signature [RFC7427] is expected to be promoted as it provides 486 hash function, signature format and algorithm agility. 488 4.1.1. Recommendations for RSA key length 490 +-------------------------------------------+------------+ 491 | Description | Status | 492 +-------------------------------------------+------------+ 493 | RSA with key length 2048 | MUST | 494 | RSA with key length 3072 and 4096 | SHOULD | 495 | RSA with key length between 2049 and 4095 | MAY | 496 | RSA with key length smaller than 2048 | SHOULD NOT | 497 +-------------------------------------------+------------+ 499 The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or 500 2048 bits, but here we make key sizes less than 2048 SHOULD NOT as 501 there is industry-wide trend to deprecate key lengths less than 2048 502 bits. 504 4.2. Digital Signature Recommendations 506 When Digital Signature authentication method is implemented, then the 507 following recommendations are applied for hash functions: 509 +--------+-------------+------------+---------+ 510 | Number | Description | Status | Comment | 511 +--------+-------------+------------+---------+ 512 | 1 | SHA1 | SHOULD NOT | | 513 | 2 | SHA2-256 | MUST | | 514 | 3 | SHA2-384 | MAY | | 515 | 4 | SHA2-512 | SHOULD | | 516 +--------+-------------+------------+---------+ 518 When Digital Signature authentication method is used with RSA 519 signature algorithm, then RSASSA-PSS MUST be supported and RSASSA- 520 PKCS1-v1.5 MAY be supported. 522 The following table lists recommendations for authentication methods 523 in RFC7427 [RFC7427] notation. These recommendations are applied 524 only if Digital Signature authentication method is implemented. 526 +------------------------------------+------------+---------+ 527 | Description | Status | Comment | 528 +------------------------------------+------------+---------+ 529 | RSASSA-PSS with SHA-256 | MUST | | 530 | ecdsa-with-sha256 | SHOULD | | 531 | sha1WithRSAEncryption | SHOULD NOT | | 532 | dsa-with-sha1 | SHOULD NOT | | 533 | ecdsa-with-sha1 | SHOULD NOT | | 534 | RSASSA-PSS with Empty Parameters | SHOULD NOT | | 535 | RSASSA-PSS with Default Parameters | SHOULD NOT | | 536 +------------------------------------+------------+---------+ 538 5. Algorithms for Internet of Things 540 Some algorithms in this document are marked for use with the Internet 541 of Things (IoT). There are several reasons why IoT devices prefer a 542 different set of algorithms from regular IKEv2 clients. IoT devices 543 are usually very constrained, meaning the memory size and CPU power 544 is so limited, that these clients only have resources to implement 545 and run one set of algorithms. For example, instead of implementing 546 AES and SHA, these devices typically use AES_XCBC as integrity 547 algorithm so SHA does not need to be implemented. 549 For example, IEEE Std 802.15.4 [IEEE-802-15-4] devices have a 550 mandatory to implement link level security using AES-CCM with 128 bit 551 keys. The IEEE Recommended Practice for Transport of Key Management 552 Protocol (KMP) Datagrams [IEEE-802-15-9] already provide a way to use 553 Minimal IKEv2 [RFC7815] over 802.15.4 to provide link keys for the 554 802.15.4 layer. 556 These devices might want to use AES-CCM as their IKEv2 algorithm, so 557 they can reuse the hardware implementing it. They cannot use the 558 AES-CBC algorithm, as the hardware quite often do not include support 559 for AES decryption needed to support the CBC mode. So despite the 560 AES-CCM algorithm requiring AEAD [RFC5282] support, the benefit of 561 reusing the crypto hardware makes AES-CCM the preferred algorithm. 563 Another important aspect of IoT devices is that their transfer rates 564 are usually quite low (in order of tens of kbits/s), and each bit 565 they transmit has an energy consumption cost associated with it and 566 shortens their battery life. Therefore, shorter packets are 567 preferred. This is the reason for recommending the 8 octet ICV over 568 the 16 octet ICV. 570 Because different IoT devices will have different constraints, this 571 document cannot specify the one mandatory profile for IoT. Instead, 572 this document points out commonly used algorithms with IoT devices. 574 6. Security Considerations 576 The security of cryptographic-based systems depends on both the 577 strength of the cryptographic algorithms chosen and the strength of 578 the keys used with those algorithms. The security also depends on 579 the engineering of the protocol used by the system to ensure that 580 there are no non-cryptographic ways to bypass the security of the 581 overall system. 583 The Diffie-Hellman Group parameter is the most important one to 584 choose conservatively. Any party capturing all IKE and ESP traffic 585 that (even years later) can break the selected DH group in IKE, can 586 gain access to the symmetric keys used to encrypt all the ESP 587 traffic. Therefore, these groups must be chosen very conservatively. 588 However, specifying an extremely large DH group also puts a 589 considerable load on the device, especially when this is a large VPN 590 gateway or an IoT constrained device. 592 This document concerns itself with the selection of cryptographic 593 algorithms for the use of IKEv2, specifically with the selection of 594 "mandatory-to-implement" algorithms. The algorithms identified in 595 this document as "MUST implement" or "SHOULD implement" are not known 596 to be broken at the current time, and cryptographic research so far 597 leads us to believe that they will likely remain secure into the 598 foreseeable future. However, this isn't necessarily forever and it 599 is expected that new revisions of this document will be issued from 600 time to time to reflect the current best practice in this area. 602 7. IANA Considerations 604 This document makes no requests of IANA. 606 8. Acknowledgements 608 The first version of this document was RFC 4307 by Jeffrey I. 609 Schiller of the Massachusetts Institute of Technology (MIT). Much of 610 the original text has been copied verbatim. 612 We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson and 613 Tommy Pauly for their valuable feedback. 615 9. References 617 9.1. Normative References 619 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 620 Requirement Levels", BCP 14, RFC 2119, 621 DOI 10.17487/RFC2119, March 1997, 622 . 624 [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode 625 (GCM) in IPsec Encapsulating Security Payload (ESP)", 626 RFC 4106, DOI 10.17487/RFC4106, June 2005, 627 . 629 [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the 630 Internet Key Exchange Version 2 (IKEv2)", RFC 4307, 631 DOI 10.17487/RFC4307, December 2005, 632 . 634 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 635 Kivinen, "Internet Key Exchange Protocol Version 2 636 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 637 2014, . 639 [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption 640 Algorithms with the Encrypted Payload of the Internet Key 641 Exchange version 2 (IKEv2) Protocol", RFC 5282, 642 DOI 10.17487/RFC5282, August 2008, 643 . 645 9.2. Informative References 647 [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in 648 the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, 649 DOI 10.17487/RFC7427, January 2015, 650 . 652 [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman 653 Tests for the Internet Key Exchange Protocol Version 2 654 (IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013, 655 . 657 [RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2 658 (IKEv2) Initiator Implementation", RFC 7815, 659 DOI 10.17487/RFC7815, March 2016, 660 . 662 [IKEV2-IANA] 663 "Internet Key Exchange Version 2 (IKEv2) Parameters", 664 . 666 [TRANSCRIPTION] 667 Bhargavan, K. and G. Leurent, "Transcript Collision 668 Attacks: Breaking Authentication in TLS, IKE, and SSH", 669 NDSS , feb 2016. 671 [IEEE-802-15-4] 672 "IEEE Standard for Low-Rate Wireless Personal Area 673 Networks (WPANs)", IEEE Standard 802.15.4, 2015. 675 [IEEE-802-15-9] 676 "IEEE Recommended Practice for Transport of Key Management 677 Protocol (KMP) Datagrams", IEEE Standard 802.15.9, 2016. 679 Authors' Addresses 681 Yoav Nir 682 Check Point Software Technologies Ltd. 683 5 Hasolelim st. 684 Tel Aviv 6789735 685 Israel 687 EMail: ynir.ietf@gmail.com 689 Tero Kivinen 690 INSIDE Secure 691 Eerikinkatu 28 692 HELSINKI FI-00180 693 FI 695 EMail: kivinen@iki.fi 697 Paul Wouters 698 Red Hat 700 EMail: pwouters@redhat.com 701 Daniel Migault 702 Ericsson 703 8400 boulevard Decarie 704 Montreal, QC H4P 2N2 705 Canada 707 Phone: +1 514-452-2160 708 EMail: daniel.migault@ericsson.com