[strongSwan] policy mismatch

[Tobias Brunner]

Hi Christian,

> When Windows connects, strongSwan gives it the wrong policy and hence
> Windows 10 reports a*policy match error*
> 
> May  1 21:53:12 08[CFG] *received proposals*:
> IKE:3DES_CBC/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:3DES_CBC/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:3DES_CBC/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
> IKE:AES_CBC_128/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:AES_CBC_128/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
> IKE:AES_CBC_192/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:AES_CBC_192/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:AES_CBC_192/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
> IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:AES_CBC_256/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
> IKE:AES_GCM_16_128/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:AES_GCM_16_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:AES_GCM_16_128/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
> IKE:AES_GCM_16_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
> IKE:AES_GCM_16_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
> IKE:AES_GCM_16_256/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024
> May  1 21:53:12 08[CFG] *configured proposals*:
> IKE:AES_GCM_16_256/AES_GCM_16_128/PRF_HMAC_SHA2_384/PRF_HMAC_SHA2_256/MODP_1024
> May  1 21:53:12 08[CFG] selected proposal:
> IKE:*AES_GCM_16_128/PRF_HMAC_SHA2_256/MODP_1024*
> 
> Expected response (I'm guessing)
> *AES_GCM_16_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024 *(although
> I dont know why it doesnt chose the better ciphers).

No, with AES-GCM there is no integrity algorithm (HMAC_SHA* here) needed
as combined-mode ciphers like AES-GCM provide both encryption and
integrity protection (see section 8 in RFC 5282 [1] and section 3.3 in
RFC 7296 [2]).
So the problem is that the client proposes invalid proposals and
probably expects an invalid proposal back.

Regards,
Tobias

[1] https://tools.ietf.org/html/rfc5282#section-8
[2] https://tools.ietf.org/html/rfc7296#section-3.3