Deprecation of IKEv1 and obsoleted algorithms (2024)

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Table of Contents

3. RFC2407, RFC2408 and RFC2409 are Historic

IKEv1 is deprecated. Systems running IKEv1 should be upgraded and reconfigured to run IKEv2. Systems that support IKEv1 but not IKEv2 are most likely also unsuitable candidates for continued operation:¶

• IKEv1 development ceased over a decade ago and no new work will happen. This poses the risk of unmaintained code in an otherwise supported product which can result in security vulnerabilities.¶
• A number of IKEv1 systems have reached their End of Life and therefor will never be patched by the vendor if a vulnerability is found.¶
• There are vendors that still provide updates for their equipment that supports IKEv1 and IKEv2, but have "frozen" their IKEv1 implementation. Such users might not be aware that they are running unmaintained code with its associated security risks.¶
• IKEv1 systems can be abused for packet amplification attacks, as documented in the Security Bulletin [CVE-2016-5361].¶
• Great strides have been made in cryptography since IKEv1 development ceased. While some modern cryptographic algorithms were added to IKEv1, interoperability concerns mean that the defacto algorithms negotiated by IKEv1 will consist of dated or deprecated algorithms like AES-CBC, SHA1, and Diffie-Hellman groups 1 or 2. IKEv2 provides state-of-the-art suite of cryptographic algorithms that IKEv1 lacks.¶

IKEv2 is a more secure protocol than IKEv1. For example, IKEv2 offers more modern cryptographic primitives, proper defense against denial of service attacks, improved authentication via EAP methods, PAKE support and is actively worked on with respect to defending against quantum computer attacks.¶

IKEv1-only systems should be upgraded or replaced by systems supporting IKEv2. IKEv2 implementations SHOULD NOT directly import IKEv1 configurations without updating the cryptographic algorithms used.¶

4. IKEv1 feature equivalents for IKEv2

A few notably IKEv1 features are not present in the IKEv2 core specification [RFC7296] but are available for IKEv2 via an additional specification:¶

5. Deprecating obsolete algorithms

This document deprecates the following algorithms:¶

• Encryption Algorithms: RC5, IDEA, CAST, Blowfish, and the unspecified 3IDEA, ENCR_DES_IV64 and ENCR_DES_IV32¶
• PRF Algorithms: the unspecified PRF_HMAC_TIGER¶
• Integrity Algorithms: HMAC-MD5-128¶
• Diffie-Hellman groups: none¶

6. Security Considerations

There are only security benefits by deprecating IKEv1 for IKEv2.¶

The deprecated algorithms have long been in disuse and are no longer actively deployed or researched. It presents an unknown security risk that is best avoided. Additionally, these algorithms not being supported in implementations simplifies those implementations and reduces the accidental use of these deprecated algorithms through misconfiguration or downgrade attacks.¶

7. IANA Considerations

This document instructs IANA to add an additional Status column to the IKEv2 Transform Type registries and mark the following entries as DEPRECATED:¶

 Transform Type 1 - Encryption Algorithm IDs Number Name Status ------ --------------- ------ 1 ENCR_DES_IV64 DEPRECATED [this document] 2 ENCR_DES DEPRECATED [RFC8247] 4 ENCR_RC5 DEPRECATED [this document] 5 ENCR_IDEA DEPRECATED [this document] 6 ENCR_CAST DEPRECATED [this document] 7 ENCR_BLOWFISH DEPRECATED [this document] 8 ENCR_3IDEA DEPRECATED [this document] 9 ENCR_DES_IV32 DEPRECATED [this document]

 Transform Type 2 - Pseudorandom Function Transform IDs Number Name Status ------ ------------ ---------- 1 PRF_HMAC_MD5 DEPRECATED [RFC8247] 1 PRF_HMAC_TIGER DEPRECATED [this document]

 Transform Type 3 - Integrity Algorithm Transform IDs Number Name Status ------ ----------------- ---------- 1 AUTH_HMAC_MD5_96 DEPRECATED [RFC8247] 3 AUTH_DES_MAC DEPRECATED [RFC8247] 4 AUTH_KPDK_MD5 DEPRECATED [RFC8247] 6 AUTH_HMAC_MD5_128 DEPRECATED [this document] 7 AUTH_HMAC_SHA1_160 DEPRECATED [this document]

 Transform Type 4 - Diffie Hellman Group Transform IDs Number Name Status ------ ---------------------------- ---------- 1 768-bit MODP Group DEPRECATED [RFC8247] 22 1024-bit MODP Group with 160-bit Prime Order Subgroup DEPRECATED [RFC8247]

All entries not mentioned here should receive no value in the new Status field.¶

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