On 1 feb 2008, at 1:59, Vishwas Manral wrote: > For ESP (RFC4303) the ICV does not cover the outer IP header at all > the mutable field or not. For AH (RFC4302) however the outer IP header > is covered for the ICV calculation.
Yes. So if you want to cryptographically protect your header, either use AH or put the packet into another packet and protect the original packet with ESP. A header checksum will give you none of this because the checksum algorithm used in IP is so simple I can calculate it in my head (just 16-bit additions over data that's in the packet). Note also that all the important fields in the IP header are included in the transport layer checksum, which also makes it unnecessary to do a separate header checksum to protect these fields against bit errors. Last but not least, if an attacker can toggle bits in your header, it really doesn't matter whether you have cryptographically strong means to detect this, because what you would be doing is dropping the packet, while any of this toggling would also result in dropping the packet at some point, all else being equal. (The attacker could also toggle bits in the data part of the packet so the receiver would accept bad data, but IPsec AH/ESP or even TLS all provide protection against that regardless of header checksums.) -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: http://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
