Supported IKE ciphers

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Cloud VPN supports the following ciphers and configuration parameters for peer VPN devices or VPN services. Cloud VPN auto-negotiates the connection as long as the peer side uses a supported IKE cipher setting.

For configuration instructions, see Configure the peer VPN gateway.

Cloud VPN operates in IPsec ESP Tunnel Mode.

The following IKE ciphers are supported for Classic VPN and HA VPN.

Proposal order

Cloud VPN can act as an initiator or a responder to IKE requests depending on the origin of traffic when a new security association (SA) is needed.

When Cloud VPN initiates a VPN connection, Cloud VPN proposes the algorithms in the order shown in the supported cipher tables for each cipher role. The peer side receiving the proposal selects an algorithm.

If the peer side initiates the connection, then Cloud VPN selects a cipher from the proposal by using the same order shown in the table for each cipher role.

Depending on which side is the initiator or the responder, the selected cipher can be different. For example, the selected cipher might even change over time as new security associations (SAs) are created during key rotation. Because a change in cipher selection can impact important tunnel characteristics such as performance or MTU, ensure that your cipher selection is stable.

To prevent frequent changes in cipher selection, configure your peer VPN gateway to propose and accept only one cipher for each cipher role. This cipher must be supported by both Cloud VPN and your peer VPN gateway. Do not provide a list of ciphers for each cipher role. This best practice ensures that both sides of your Cloud VPN tunnel always select the same IKE cipher during IKE negotiation.

For HA VPN tunnel pairs, configure both HA VPN tunnels on your peer VPN gateway to use the same cipher and IKE Phase 2 lifetime values.

Supported cipher tables

IKEv2 ciphers that use AEAD

The following ciphers use authenticated encryption with associated data (AEAD).

Phase 1

Cipher role Cipher Notes
Encryption & Integrity
  • AES-GCM-16-128
  • AES-GCM-16-192
  • AES-GCM-16-256

In this list, the first number is the size of the ICV parameter in bytes (octets), and the second is the key length in bits.

Some documentation might express the ICV parameter (the first number) in bits instead (8 becomes 64, 12 becomes 96, and 16 becomes 128).

Pseudo-Random Function (PRF)
  • PRF-AES128-XCBC
  • PRF-AES128-CMAC
  • PRF-HMAC-SHA1
  • PRF-HMAC-MD5
  • PRF-HMAC-SHA2-256
  • PRF-HMAC-SHA2-384
  • PRF-HMAC-SHA2-512
Many devices don't require an explicit PRF setting.
Diffie-Hellman (DH)
  • modp_2048 (Group 14)
  • modp_2048_224 (modp_2048s224)
  • modp_2048_256 (modp_2048s256)
  • modp_1536 (Group 5)
  • modp_3072 (Group 15)
  • modp_4096 (Group 16)
  • modp_8192 (Group 18)
  • modp_1024 (Group 2)
  • modp_1024_160 (modp_1024s160)
  • ecp_256 (Group 19)
  • ecp_384 (Group 20)
  • ecp_521 (Group 21)
  • curve_25519 (Group 31)
Phase 1 lifetime 36,000 seconds (10 hours)

Phase 2

Cipher role Cipher Notes
Encryption & Integrity
  • AES-GCM-16-128
  • AES-GCM-16-256
  • AES-GCM-16-192

The first number in each algorithm is the size of the ICV parameter in bytes (octets), and the second is its key length in bits. Some documentation might express the ICV parameter (the first number) in bits instead (8 becomes 64, 12 becomes 96, 16 becomes 128).

PFS Algorithm (required)
  • modp_2048 (Group 14)
  • modp_2048_224 (modp_2048s224)
  • modp_2048_256 (modp_2048s256)
  • modp_1536 (Group 5)
  • modp_3072 (Group 15)
  • modp_4096 (Group 16)
  • modp_8192 (Group 18)
  • modp_1024 (Group 2)
  • modp_1024_160 (modp_1024s160)
  • ecp_256 (Group 19)
  • ecp_384 (Group 20)
  • ecp_521 (Group 21)
  • curve_25519 (Group 31)
Diffie-Hellman (DH) Refer to Phase 1. If your VPN gateway requires DH settings for Phase 2, use the same settings that you used for Phase 1.
Phase 2 lifetime 10,800 seconds (3 hours)

IKEv2 ciphers that don't use AEAD

Phase 1

Cipher role Cipher Notes
Encryption
  • AES-CBC-128
  • AES-CBC-192
  • AES-CBC-256
  • 3DES-CBC
  • AES-XCBC-96
  • AES-CMAC-96
Integrity
  • HMAC-SHA1-96
  • HMAC-MD5-96
  • HMAC-SHA2-256-128
  • HMAC-SHA2-384-192
  • HMAC-SHA2-512-256

Documentation for your on-premises VPN gateway might use a slightly different name for the algorithm. For example, HMAC-SHA2-512-256 might be referred to as SHA2-512 or SHA-512, dropping the truncation length number and other extraneous information.

Pseudo-Random Function (PRF)
  • PRF-AES-128-XCBC
  • PRF-AES-128-CMAC
  • PRF-SHA1
  • PRF-MD5
  • PRF-SHA2-256
  • PRF-SHA2-384
  • PRF-SHA2-512
Many devices don't require an explicit PRF setting.
Diffie-Hellman (DH)
  • modp_2048 (Group 14)
  • modp_2048_224 (modp_2048s224)
  • modp_2048_256 (modp_2048s256)
  • modp_1536 (Group 5)
  • modp_3072 (Group 15)
  • modp_4096 (Group 16)
  • modp_8192 (Group 18)
  • modp_1024 (Group 2)
  • modp_1024_160 (modp_1024s160)
  • ecp_256 (Group 19)
  • ecp_384 (Group 20)
  • ecp_521 (Group 21)
  • curve_25519 (Group 31)
Phase 1 lifetime 36,000 seconds (10 hours)

Phase 2

Cipher role Cipher Notes
Encryption
  • AES-CBC-128
  • AES-CBC-256
  • AES-CBC-192
Integrity
  • HMAC-SHA2-256-128
  • HMAC-SHA2-512-256
  • HMAC-SHA1-96

Documentation for your on-premises VPN gateway might use a slightly different name for the algorithm. For example, HMAC-SHA2-512-256 might be referred to as SHA2-512 or SHA-512, dropping the truncation length number and other extraneous information.

PFS Algorithm (required)
  • modp_2048 (Group 14)
  • modp_2048_224 (modp_2048s224)
  • modp_2048_256 (modp_2048s256)
  • modp_1536 (Group 5)
  • modp_3072 (Group 15)
  • modp_4096 (Group 16)
  • modp_8192 (Group 18)
  • modp_1024 (Group 2)
  • modp_1024_160 (modp_1024s160)
  • ecp_256 (Group 19)
  • ecp_384 (Group 20)
  • ecp_521 (Group 21)
  • curve_25519 (Group 31)
Diffie-Hellman (DH) Refer to Phase 1. If your VPN gateway requires DH settings for Phase 2, use the same settings that you used for Phase 1.
Phase 2 lifetime 10,800 seconds (3 hours)

IKEv1 ciphers

Phase 1

Cipher role Cipher
Encryption AES-CBC-128
Integrity HMAC-SHA1-96
Pseudo-Random Function (PRF)* PRF-SHA1-96
Diffie-Hellman (DH) modp_1024 (Group 2)
Phase 1 lifetime 36,600 seconds (10 hours, 10 minutes)

*For more information about PRF in IKEv1, see RFC 2409.

Phase 2

Cipher role Cipher
Encryption AES-CBC-128
Integrity HMAC-SHA1-96
PFS Algorithm (required) modp_1024 (Group 2)
Diffie-Hellman (DH) If you need to specify DH for your VPN gateway, use the same setting that you used for Phase 1.
Phase 2 lifetime 10,800 seconds (3 hours)

What's next

  • To learn about the basic concepts of Cloud VPN, see the Cloud VPN overview.
  • To help you solve common issues that you might encounter when using Cloud VPN, see Troubleshooting.