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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 14, 2016 Red Hat 8 D. Migault 9 Ericsson 10 May 13, 2016 12 Algorithm Implementation Requirements and Usage Guidance for IKEv2 13 draft-ietf-ipsecme-rfc4307bis-09 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 14, 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 . . . . . . . . . . . . . . 5 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 . . . . 7 72 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 8 73 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 9 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 . . . . . . . . . . . . 12 78 5. Algorithms for Internet of Things . . . . . . . . . . . . . . 12 79 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 80 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 81 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 82 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 83 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 84 9.2. Informative References . . . . . . . . . . . . . . . . . 15 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. 177 This document does not give any recommendations for the use of 178 algorithms, it only gives implementation recommendations for 179 implementations. The use of algorithms by users is dictated by the 180 security policy requirements for that specific user, and are outside 181 the scope of this document. 183 IKEv1 is out of scope of this document. IKEv1 is deprecated and the 184 recommendations of this document must not be considered for IKEv1, as 185 most IKEv1 implementations have been "frozen" and will not be able to 186 update the list of mandatory-to-implement algorithms. 188 2. Conventions Used in This Document 190 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 191 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 192 document are to be interpreted as described in [RFC2119]. 194 We define some additional terms here: 196 SHOULD+ This term means the same as SHOULD. However, it is likely 197 that an algorithm marked as SHOULD+ will be promoted at 198 some future time to be a MUST. 199 SHOULD- This term means the same as SHOULD. However, an algorithm 200 marked as SHOULD- may be deprecated to a MAY in a future 201 version of this document. 202 MUST- This term means the same as MUST. However, we expect at 203 some point that this algorithm will no longer be a MUST in 204 a future document. Although its status will be determined 205 at a later time, it is reasonable to expect that if a 206 future revision of a document alters the status of a MUST- 207 algorithm, it will remain at least a SHOULD or a SHOULD- 208 level. 209 IoT stands for Internet of Things. 211 3. Algorithm Selection 213 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms 215 The algorithms in the below table are negotiated in the SA payload 216 and used for the Encrypted Payload. References to the specification 217 defining these algorithms and the ones in the following subsections 218 are in the IANA registry [IKEV2-IANA]. Some of these algorithms are 219 Authenticated Encryption with Associated Data (AEAD - [RFC5282]). 220 Algorithms that are not AEAD MUST be used in conjunction with an 221 integrity algorithms in Section 3.3. 223 +-----------------------------+----------+-------+----------+ 224 | Name | Status | AEAD? | Comment | 225 +-----------------------------+----------+-------+----------+ 226 | ENCR_AES_CBC | MUST- | No | [1] | 227 | ENCR_CHACHA20_POLY1305 | SHOULD | Yes | | 228 | AES-GCM with a 16 octet ICV | SHOULD | Yes | [1] | 229 | ENCR_AES_CCM_8 | SHOULD | Yes | [1][IoT] | 230 | ENCR_3DES | MAY | No | | 231 | ENCR_DES | MUST NOT | No | | 232 +-----------------------------+----------+-------+----------+ 234 [1] - This requirement level is for 128-bit keys. 256-bit keys are at 235 SHOULD. 192-bit keys can safely be ignored. [IoT] - This requirement 236 is for interoperability with IoT. 238 ENCR_AES_CBC is raised from SHOULD+ in [RFC4307] to MUST. It is the 239 only shared mandatory-to-implement algorithm with RFC4307 and as a 240 result it is necessary for interoperability with IKEv2 implementation 241 compatible with RFC4307. 243 ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of 244 RFC4307. It has been recommended by the CRFG and others as an 245 alternative to AES-CBC and AES-GCM. It is also being standardized 246 for IPsec for the same reasons. At the time of writing, there were 247 not enough IKEv2 implementations supporting ENCR_CHACHA20_POLY1305 to 248 be able to introduce it at the SHOULD+ level. 250 AES-GCM with a 16 octet ICV was not considered in RFC4307. At the 251 time RFC4307 was written, AES-GCM was not defined in an IETF 252 document. AES-GCM was defined for ESP in [RFC4106] and later for 253 IKEv2 in [RFC5282]. The main motivation for adopting AES-GCM for ESP 254 is encryption performance and key longevity compared to AES-CBC. 255 This resulted in AES-GCM being widely implemented for ESP. As the 256 computation load of IKEv2 is relatively small compared to ESP, many 257 IKEv2 implementations have not implemented AES-GCM. For this reason, 258 AES-GCM is not promoted to a greater status than SHOULD. The reason 259 for promotion from MAY to SHOULD is to promote the slightly more 260 secure AEAD method over the traditional encrypt+auth method. Its 261 status is expected to be raised once widely implemented. As the 262 advantage of the shorter (and weaker) ICVs is minimal, the 8 and 12 263 octet ICV's remain at the MAY level. 265 ENCR_AES_CCM_8 was not considered in RFC4307. This document 266 considers it as SHOULD be implemented in order to be able to interact 267 with Internet of Things devices. As this case is not a general use 268 case for non-IoT VPNs, its status is expected to remain as SHOULD. 269 The 8 octet size of the ICV is expected to be sufficient for most use 270 cases of IKEv2, as far less packets are exchanged on those cases, and 271 IoT devices want to make packets as small as possible. When 272 implemented, ENCR_AES_CCM_8 MUST be implemented for key length 128 273 and MAY be implemented for key length 256. 275 ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All 276 IKEv2 implementation already implement ENCR_AES_CBC, so there is no 277 need to keep support for the much slower ENCR_3DES. In addition, 278 ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES. 280 ENCR_DES can be brute-forced using of-the-shelves hardware. It 281 provides no meaningful security whatsoever and therefor MUST NOT be 282 implemented. 284 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms 286 Transform Type 2 algorithms are pseudo-random functions used to 287 generate pseudo-random values when needed. 289 If an algorithm is selected as the integrity algorithm, it SHOULD 290 also be used as the PRF. When using an AEAD cipher, a choice of PRF 291 needs to be made. The table below lists the recommended algorithms. 293 +-------------------+----------+---------+ 294 | Name | Status | Comment | 295 +-------------------+----------+---------+ 296 | PRF_HMAC_SHA2_256 | MUST | | 297 | PRF_HMAC_SHA2_512 | SHOULD+ | | 298 | PRF_HMAC_SHA1 | MUST- | | 299 | PRF_AES128_XCBC | SHOULD | [IoT] | 300 | PRF_HMAC_MD5 | MUST NOT | | 301 +-------------------+----------+---------+ 303 [IoT] - This requirement is for interoperability with IoT 305 PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based 306 transforms were mentioned. PRF_HMAC_SHA2_256 MUST be implemented in 307 order to replace SHA1 and PRF_HMAC_SHA1. 309 PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for 310 PRF_HMAC_SHA2_256 or when stronger security is required. 311 PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the 312 additional overhead of PRF_HMAC_SHA2_512 is negligible. 314 PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as 315 their is an industry-wide trend to deprecate its usage. 317 PRF_AES128_XCBC is only recommended in the scope of IoT, as Internet 318 of Things deployments tend to prefer AES based pseudo-random 319 functions in order to avoid implementing SHA2. For the non-IoT VPN 320 deployment it has been downgraded from SHOULD in RFC4307 to MAY as it 321 has not seen wide adoption. 323 PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT. 324 There is an industry-wide trend to deprecate its usage as MD5 support 325 is being removed from cryptographic libraries in general because its 326 non-HMAC use is known to be subject to collision attacks, for example 327 as mentioned in [TRANSCRIPTION]. 329 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms 331 The algorithms in the below table are negotiated in the SA payload 332 and used for the Encrypted Payload. References to the specification 333 defining these algorithms are in the IANA registry. When an AEAD 334 algorithm (see Section 3.1) is proposed, this algorithm transform 335 type is not in use. 337 +------------------------+----------+---------+ 338 | Name | Status | Comment | 339 +------------------------+----------+---------+ 340 | AUTH_HMAC_SHA2_256_128 | MUST | | 341 | AUTH_HMAC_SHA2_512_256 | SHOULD | | 342 | AUTH_HMAC_SHA1_96 | MUST- | | 343 | AUTH_AES_XCBC_96 | SHOULD | [IoT] | 344 | AUTH_HMAC_MD5_96 | MUST NOT | | 345 | AUTH_DES_MAC | MUST NOT | | 346 | AUTH_KPDK_MD5 | MUST NOT | | 347 +------------------------+----------+---------+ 349 [IoT] - This requirement is for interoperability with IoT 351 AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based 352 transforms were mentioned. AUTH_HMAC_SHA2_256_128 MUST be 353 implemented in order to replace AUTH_HMAC_SHA1_96. 355 AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement 356 of AUTH_HMAC_SHA2_256_128 or when stronger security is required. 357 This value has been preferred over AUTH_HMAC_SHA2_384, as the 358 additional overhead of AUTH_HMAC_SHA2_512 is negligible. 360 AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST- 361 as there is an industry-wide trend to deprecate its usage. 363 AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of 364 Things deployments tend to prefer AES based pseudo-random functions 365 in order to avoid implementing SHA2. For the non-IoT VPN deployment, 366 it has been downgraded from SHOULD in RFC4307 to MAY as it has not 367 been widely adopted. 369 AUTH_DES_MAC, AUTH_HMAC_MD5_96, and AUTH_KPDK_MD5 were not mentioned 370 in RFC4307 so their default status ware MAY. They have been 371 downgraded to MUST NOT. There is an industry-wide trend to deprecate 372 DES and MD5. MD5 support is being removed from cryptographic 373 libraries in general because its non-HMAC use is known to be subject 374 to collision attacks, for example as mentioned in [TRANSCRIPTION]. 376 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 378 There are several Modular Exponential (MODP) groups and several 379 Elliptic Curve groups (ECC) that are defined for use in IKEv2. These 380 groups are defined in both the [IKEv2] base document and in 381 extensions documents and are identified by group number. Note that 382 it is critical to enforce a secure Diffie-Hellman exchange as this 383 exchange provides keys for the session. If an attacker can retrieve 384 the private numbers (a, or b) and the public values (g**a, and g**b), 385 then the attacker can compute the secret and the keys used and 386 decrypt the exchange and IPsec SA created inside the IKEv2 SA. Such 387 an attack can be performed off-line on a previously recorded 388 communication, years after the communication happened. This differs 389 from attacks that need to be executed during the authentication which 390 must be performed online and in near real-time. 392 +--------+---------------------------------------------+------------+ 393 | Number | Description | Status | 394 +--------+---------------------------------------------+------------+ 395 | 14 | 2048-bit MODP Group | MUST | 396 | 19 | 256-bit random ECP group | SHOULD | 397 | 5 | 1536-bit MODP Group | SHOULD NOT | 398 | 2 | 1024-bit MODP Group | SHOULD NOT | 399 | 1 | 768-bit MODP Group | MUST NOT | 400 | 22 | 1024-bit MODP Group with 160-bit Prime | SHOULD NOT | 401 | | Order Subgroup | | 402 | 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT | 403 | | Order Subgroup | | 404 | 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT | 405 | | Order Subgroup | | 406 +--------+---------------------------------------------+------------+ 408 Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as 409 a replacement for 1024-bit MODP Group. Group 14 is widely 410 implemented and considered secure. 412 Group 19 or 256-bit random ECP group was not specified in RFC4307, as 413 this group were not specified at that time. Group 19 is widely 414 implemented and considered secure. 416 Group 5 or 1536-bit MODP Group has been downgraded from MAY in 417 RFC4307 to SHOULD NOT. It was specified earlier, but is now 418 considered to be vulnerable to be broken within the next few years by 419 a nation state level attack, so its security margin is considered too 420 narrow. 422 Group 2 or 1024-bit MODP Group has been downgraded from MUST- in 423 RFC4307 to SHOULD NOT. It is known to be weak against sufficiently 424 funded attackers using commercially available mass-computing 425 resources, so its security margin is considered too narrow. It is 426 expected in the near future to be downgraded to MUST NOT. 428 Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its 429 status was MAY. It can be broken within hours using cheap of-the- 430 shelves hardware. It provides no security whatsoever. 432 Group 22, 23 and 24 or 1024-bit MODP Group with 160-bit, and 2048-bit 433 MODP Group with 224-bit and 256-bit Prime Order Subgroup have small 434 subgroups, which means that checks specified in the "Additional 435 Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2 first bullet 436 point MUST be done when these groups are used. These groups are also 437 not safe-primes. The seeds for these groups have not been publicly 438 released, resulting in reduced trust in these groups. These groups 439 were proposed as alternatives for group 2 and 14 but never saw wide 440 deployment. It is expected in the near future to be further 441 downgraded to MUST NOT. 443 4. IKEv2 Authentication 445 IKEv2 authentication may involve a signatures verification. 446 Signatures may be used to validate a certificate or to check the 447 signature of the AUTH value. Cryptographic recommendations regarding 448 certificate validation are out of scope of this document. What is 449 mandatory to implement is provided by the PKIX Community. This 450 document is mostly concerned on signature verification and generation 451 for the authentication. 453 4.1. IKEv2 Authentication Method 454 +--------+---------------------------------------+------------+ 455 | Number | Description | Status | 456 +--------+---------------------------------------+------------+ 457 | 1 | RSA Digital Signature | MUST | 458 | 2 | Shared Key Message Integrity Code | MUST | 459 | 3 | DSS Digital Signature | SHOULD NOT | 460 | 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD | 461 | 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD | 462 | 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD | 463 | 14 | Digital Signature | SHOULD | 464 +--------+---------------------------------------+------------+ 466 RSA Digital Signature is widely deployed and therefore kept for 467 interoperability. It is expected to be downgraded in the future as 468 its signatures are based on the older RSASSA-PKCS1-v1.5 which is no 469 longer recommended. RSA authentication, as well as other specific 470 Authentication Methods, are expected to be replaced with the generic 471 Digital Signature method of [RFC7427]. RSA Digital Signature is not 472 recommended for keys smaller then 2048, but since these signatures 473 only have value in real-time, and need no future protection, smaller 474 keys was kept at SHOULD NOT instead of MUST NOT. 476 Shared Key Message Integrity Code is widely deployed and mandatory to 477 implement in the IKEv2 in the RFC7296. 479 ECDSA based Authentication Methods are also expected to be downgraded 480 as it does not provide hash function agility. Instead, ECDSA (like 481 RSA) is expected to be performed using the generic Digital Signature 482 method. 484 DSS Digital Signature is bound to SHA-1 and has the same level of 485 security as 1024-bit RSA. It is expected to be downgraded to MUST 486 NOT in the future. 488 Digital Signature [RFC7427] is expected to be promoted as it provides 489 hash function, signature format and algorithm agility. 491 4.1.1. Recommendations for RSA key length 493 +-------------------------------------------+------------+ 494 | Description | Status | 495 +-------------------------------------------+------------+ 496 | RSA with key length 2048 | MUST | 497 | RSA with key length 3072 and 4096 | SHOULD | 498 | RSA with key length between 2049 and 4095 | MAY | 499 | RSA with key length smaller than 2048 | SHOULD NOT | 500 +-------------------------------------------+------------+ 502 The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or 503 2048 bits, but here we make key sizes less than 2048 SHOULD NOT as 504 there is industry-wide trend to deprecate key lengths less than 2048 505 bits. 507 4.2. Digital Signature Recommendations 509 When Digital Signature authentication method is implemented, then the 510 following recommendations are applied for hash functions: 512 +--------+-------------+----------+---------+ 513 | Number | Description | Status | Comment | 514 +--------+-------------+----------+---------+ 515 | 1 | SHA1 | MUST NOT | | 516 | 2 | SHA2-256 | MUST | | 517 | 3 | SHA2-384 | MAY | | 518 | 4 | SHA2-512 | SHOULD | | 519 +--------+-------------+----------+---------+ 521 When Digital Signature authentication method is used with RSA 522 signature algorithm, then RSASSA-PSS MUST be supported and RSASSA- 523 PKCS1-v1.5 MAY be supported. 525 The following table lists recommendations for authentication methods 526 in RFC7427 [RFC7427] notation. These recommendations are applied 527 only if Digital Signature authentication method is implemented. 529 +------------------------------------+----------+---------+ 530 | Description | Status | Comment | 531 +------------------------------------+----------+---------+ 532 | RSASSA-PSS with SHA-256 | MUST | | 533 | ecdsa-with-sha256 | SHOULD | | 534 | sha1WithRSAEncryption | MUST NOT | | 535 | dsa-with-sha1 | MUST NOT | | 536 | ecdsa-with-sha1 | MUST NOT | | 537 | RSASSA-PSS with Empty Parameters | MUST NOT | | 538 | RSASSA-PSS with Default Parameters | MUST NOT | | 539 +------------------------------------+----------+---------+ 541 5. Algorithms for Internet of Things 543 Some algorithms in this document are marked for use with the Internet 544 of Things (IoT). There are several reasons why IoT devices prefer a 545 different set of algorithms from regular IKEv2 clients. IoT devices 546 are usually very constrained, meaning the memory size and CPU power 547 is so limited, that these clients only have resources to implement 548 and run one set of algorithms. For example, instead of implementing 549 AES and SHA, these devices typically use AES_XCBC as integrity 550 algorithm so SHA does not need to be implemented. 552 For example, IEEE Std 802.15.4 [IEEE-802-15-4] devices have a 553 mandatory to implement link level security using AES-CCM with 128 bit 554 keys. The IEEE Recommended Practice for Transport of Key Management 555 Protocol (KMP) Datagrams [IEEE-802-15-9] already provide a way to use 556 Minimal IKEv2 [RFC7815] over 802.15.4 to provide link keys for the 557 802.15.4 layer. 559 These devices might want to use AES-CCM as their IKEv2 algorithm, so 560 they can reuse the hardware implementing it. They cannot use the 561 AES-CBC algorithm, as the hardware quite often do not include support 562 for AES decryption needed to support the CBC mode. So despite the 563 AES-CCM algorithm requiring AEAD [RFC5282] support, the benefit of 564 reusing the crypto hardware makes AES-CCM the preferred algorithm. 566 Another important aspect of IoT devices is that their transfer rates 567 are usually quite low (in order of tens of kbits/s), and each bit 568 they transmit has an energy consumption cost associated with it and 569 shortens their battery life. Therefore, shorter packets are 570 preferred. This is the reason for recommending the 8 octet ICV over 571 the 16 octet ICV. 573 Because different IoT devices will have different constraints, this 574 document cannot specify the one mandatory profile for IoT. Instead, 575 this document points out commonly used algorithms with IoT devices. 577 6. Security Considerations 579 The security of cryptographic-based systems depends on both the 580 strength of the cryptographic algorithms chosen and the strength of 581 the keys used with those algorithms. The security also depends on 582 the engineering of the protocol used by the system to ensure that 583 there are no non-cryptographic ways to bypass the security of the 584 overall system. 586 The Diffie-Hellman Group parameter is the most important one to 587 choose conservatively. Any party capturing all IKE and ESP traffic 588 that (even years later) can break the selected DH group in IKE, can 589 gain access to the symmetric keys used to encrypt all the ESP 590 traffic. Therefore, these groups must be chosen very conservatively. 591 However, specifying an extremely large DH group also puts a 592 considerable load on the device, especially when this is a large VPN 593 gateway or an IoT constrained device. 595 This document concerns itself with the selection of cryptographic 596 algorithms for the use of IKEv2, specifically with the selection of 597 "mandatory-to-implement" algorithms. The algorithms identified in 598 this document as "MUST implement" or "SHOULD implement" are not known 599 to be broken at the current time, and cryptographic research so far 600 leads us to believe that they will likely remain secure into the 601 foreseeable future. However, this isn't necessarily forever and it 602 is expected that new revisions of this document will be issued from 603 time to time to reflect the current best practice in this area. 605 7. IANA Considerations 607 This document makes no requests of IANA. 609 8. Acknowledgements 611 The first version of this document was RFC 4307 by Jeffrey I. 612 Schiller of the Massachusetts Institute of Technology (MIT). Much of 613 the original text has been copied verbatim. 615 We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson and 616 Tommy Pauly for their valuable feedback. 618 9. References 620 9.1. Normative References 622 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 623 Requirement Levels", BCP 14, RFC 2119, 624 DOI 10.17487/RFC2119, March 1997, 625 . 627 [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode 628 (GCM) in IPsec Encapsulating Security Payload (ESP)", 629 RFC 4106, DOI 10.17487/RFC4106, June 2005, 630 . 632 [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the 633 Internet Key Exchange Version 2 (IKEv2)", RFC 4307, 634 DOI 10.17487/RFC4307, December 2005, 635 . 637 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 638 Kivinen, "Internet Key Exchange Protocol Version 2 639 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 640 2014, . 642 [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption 643 Algorithms with the Encrypted Payload of the Internet Key 644 Exchange version 2 (IKEv2) Protocol", RFC 5282, 645 DOI 10.17487/RFC5282, August 2008, 646 . 648 9.2. Informative References 650 [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in 651 the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, 652 DOI 10.17487/RFC7427, January 2015, 653 . 655 [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman 656 Tests for the Internet Key Exchange Protocol Version 2 657 (IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013, 658 . 660 [RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2 661 (IKEv2) Initiator Implementation", RFC 7815, 662 DOI 10.17487/RFC7815, March 2016, 663 . 665 [IKEV2-IANA] 666 "Internet Key Exchange Version 2 (IKEv2) Parameters", 667 . 669 [TRANSCRIPTION] 670 Bhargavan, K. and G. Leurent, "Transcript Collision 671 Attacks: Breaking Authentication in TLS, IKE, and SSH", 672 NDSS , feb 2016. 674 [IEEE-802-15-4] 675 "IEEE Standard for Low-Rate Wireless Personal Area 676 Networks (WPANs)", IEEE Standard 802.15.4, 2015. 678 [IEEE-802-15-9] 679 "IEEE Recommended Practice for Transport of Key Management 680 Protocol (KMP) Datagrams", IEEE Standard 802.15.9, 2016. 682 Authors' Addresses 683 Yoav Nir 684 Check Point Software Technologies Ltd. 685 5 Hasolelim st. 686 Tel Aviv 6789735 687 Israel 689 EMail: ynir.ietf@gmail.com 691 Tero Kivinen 692 INSIDE Secure 693 Eerikinkatu 28 694 HELSINKI FI-00180 695 FI 697 EMail: kivinen@iki.fi 699 Paul Wouters 700 Red Hat 702 EMail: pwouters@redhat.com 704 Daniel Migault 705 Ericsson 706 8400 boulevard Decarie 707 Montreal, QC H4P 2N2 708 Canada 710 Phone: +1 514-452-2160 711 EMail: daniel.migault@ericsson.com