• Jason A. Donenfeld's avatar
    siphash: add cryptographically secure PRF · 2c956a60
    Jason A. Donenfeld authored
    SipHash is a 64-bit keyed hash function that is actually a
    cryptographically secure PRF, like HMAC. Except SipHash is super fast,
    and is meant to be used as a hashtable keyed lookup function, or as a
    general PRF for short input use cases, such as sequence numbers or RNG
    For the first usage:
    There are a variety of attacks known as "hashtable poisoning" in which an
    attacker forms some data such that the hash of that data will be the
    same, and then preceeds to fill up all entries of a hashbucket. This is
    a realistic and well-known denial-of-service vector. Currently
    hashtables use jhash, which is fast but not secure, and some kind of
    rotating key scheme (or none at all, which isn't good). SipHash is meant
    as a replacement for jhash in these cases.
    There are a modicum of places in the kernel that are vulnerable to
    hashtable poisoning attacks, either via userspace vectors or network
    vectors, and there's not a reliable mechanism inside the kernel at the
    moment to fix it. The first step toward fixing these issues is actually
    getting a secure primitive into the kernel for developers to use. Then
    we can, bit by bit, port things over to it as deemed appropriate.
    While SipHash is extremely fast for a cryptographically secure function,
    it is likely a bit slower than the insecure jhash, and so replacements
    will be evaluated on a case-by-case basis based on whether or not the
    difference in speed is negligible and whether or not the current jhash usage
    poses a real security risk.
    For the second usage:
    A few places in the kernel are using MD5 or SHA1 for creating secure
    sequence numbers, syn cookies, port numbers, or fast random numbers.
    SipHash is a faster and more fitting, and more secure replacement for MD5
    in those situations. Replacing MD5 and SHA1 with SipHash for these uses is
    obvious and straight-forward, and so is submitted along with this patch
    series. There shouldn't be much of a debate over its efficacy.
    Dozens of languages are already using this internally for their hash
    tables and PRFs. Some of the BSDs already use this in their kernels.
    SipHash is a widely known high-speed solution to a widely known set of
    problems, and it's time we catch-up.
    Signed-off-by: 's avatarJason A. Donenfeld <Jason@zx2c4.com>
    Reviewed-by: 's avatarJean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Eric Biggers <ebiggers3@gmail.com>
    Cc: David Laight <David.Laight@aculab.com>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
siphash.c 4.83 KB