Why pfSense doesn't support larger DH groups?

  • Hi,

    Since m0n0wall and now with pfSense, I've been wondering why it doesn't support larger Diffie-Hellman groups as defined by RFC 3526 (http://www.ietf.org/rfc/rfc3526.txt).

    The largest supported group is DH 5 (MODP 1536 bits), which is roughly equivalent to 96-bit symmetric key. I don't think ciphers with longer key such as 3DES, CAST, Blowfish and AES would be any useful without the larger groups.

    ipsec-tools racoon does support larger DH groups in Linux. I don't know if it does so in FreeBSD, would somebody confirm or rebut this? Thanks.

    Table 1. DH keysize and security (equivalent symmetric key size)

    DH    Security  SuitableCipher
    1024  80      Skipjack
    1536  96      –-
    2048  112      3DES
    3072  128      AES128
    4840  160      AES192
    7680  192      AES192

  • It is my understanding that we support everything that the freebsd kernel + racoon supports.  Feel free to supply diff's in unified format if this is not the case.