Apple iPhone/iPad iOS IPSec IKEv2 Proposals

When setting up VPN-tunnel from an Apple iPhone or iPad running iOS using IPSec with IKEv2 you need to know, which IPSec proposals the iPhone/iPad/iOS device are supporting/offering:

Offered proposals from iOS

Testing with an iPhone running iOS 12.4.1 and iPad 13.1.2:

• AES256-SHA256-DH14 (2048-bit MODP Group) <------ (✔ okay)
• AES256-SHA256-DH19 (256-bit random ECP group) <------ (✅ recommended)
• AES256-SHA256-DH5 (1536-bit MODP Group) <------ (❌not recommended)
• AES128-SHA1-DH2 (1024-bit MODP Group) <------ (❌not recommended)
• 3DES-SHA1-DH2 (1024-bit MODP Group) <------ (❌not recommended)

Recommendation

Therefore I recommened 🔒✅ to use for your IPSec IKEv2 proposals:

• IKEv2 Phase1: AES-CBC-256 with SHA2-256 and DH-Grp 19 (ECP 256bit)
• IKEv2 Phase2: AES-CBC-256 with SHA2-256 and DH-Grp 19 (ECP 256bit)

DH-Grp 19 ECP 256Bit > DH-Grp 14 RSA 2048Bit
-> For example see BSI recommendation for crypto IPSec page 13 section 3.2.4  or NIST recommendation page 9 line 264

-> Details for ECP (Elliptic Curve from NIST) for IKEv1/v2 see RFC5903 or IANA ipsec registry

Details to reverse engineering

iPhone iOS 12.4.1 IKEv2 RAW output:

2019-10-27 16:25:15.519164 ike 4: incoming proposal:
2019-10-27 16:25:15.519176 ike 4: proposal id = 1:
2019-10-27 16:25:15.519185 ike 4:   protocol = IKEv2:
2019-10-27 16:25:15.519195 ike 4:      encapsulation = IKEv2/none
2019-10-27 16:25:15.519205 ike 4:         type=ENCR, val=AES_CBC (key_len = 256)
2019-10-27 16:25:15.519215 ike 4:         type=INTEGR, val=AUTH_HMAC_SHA2_256_128
2019-10-27 16:25:15.519224 ike 4:         type=PRF, val=PRF_HMAC_SHA2_256
2019-10-27 16:25:15.519234 ike 4:         type=DH_GROUP, val=MODP2048.
2019-10-27 16:25:15.519246 ike 4: proposal id = 2:
2019-10-27 16:25:15.519255 ike 4:   protocol = IKEv2:
2019-10-27 16:25:15.519264 ike 4:      encapsulation = IKEv2/none
2019-10-27 16:25:15.519274 ike 4:         type=ENCR, val=AES_CBC (key_len = 256)
2019-10-27 16:25:15.519283 ike 4:         type=INTEGR, val=AUTH_HMAC_SHA2_256_128
2019-10-27 16:25:15.519293 ike 4:         type=PRF, val=PRF_HMAC_SHA2_256
2019-10-27 16:25:15.519303 ike 4:         type=DH_GROUP, val=ECP256.
2019-10-27 16:25:15.519314 ike 4: proposal id = 3:
2019-10-27 16:25:15.519323 ike 4:   protocol = IKEv2:
2019-10-27 16:25:15.519332 ike 4:      encapsulation = IKEv2/none
2019-10-27 16:25:15.519342 ike 4:         type=ENCR, val=AES_CBC (key_len = 256)
2019-10-27 16:25:15.519353 ike 4:         type=INTEGR, val=AUTH_HMAC_SHA2_256_128
2019-10-27 16:25:15.519365 ike 4:         type=PRF, val=PRF_HMAC_SHA2_256
2019-10-27 16:25:15.519374 ike 4:         type=DH_GROUP, val=MODP1536.
2019-10-27 16:25:15.519384 ike 4: proposal id = 4:
2019-10-27 16:25:15.519392 ike 4:   protocol = IKEv2:
2019-10-27 16:25:15.519400 ike 4:      encapsulation = IKEv2/none
2019-10-27 16:25:15.519408 ike 4:         type=ENCR, val=AES_CBC (key_len = 128)
2019-10-27 16:25:15.519416 ike 4:         type=INTEGR, val=AUTH_HMAC_SHA_96
2019-10-27 16:25:15.519424 ike 4:         type=PRF, val=PRF_HMAC_SHA
2019-10-27 16:25:15.519432 ike 4:         type=DH_GROUP, val=MODP1024.
2019-10-27 16:25:15.519443 ike 4: proposal id = 5:
2019-10-27 16:25:15.519451 ike 4:   protocol = IKEv2:
2019-10-27 16:25:15.519459 ike 4:      encapsulation = IKEv2/none
2019-10-27 16:25:15.519466 ike 4:         type=ENCR, val=3DES_CBC
2019-10-27 16:25:15.519474 ike 4:         type=INTEGR, val=AUTH_HMAC_SHA_96
2019-10-27 16:25:15.519482 ike 4:         type=PRF, val=PRF_HMAC_SHA
2019-10-27 16:25:15.519490 ike 4:         type=DH_GROUP, val=MODP1024.