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    SubjectRe: constant half-byte from /proc/sys/kernel/random/uuid
    On Tue, 2010-06-01 at 16:22 +0400, Petr Ovtchenkov wrote:
    > Lack of randomness during generating uuid.
    [...]
    > See on 7th high half-byte: it '4' in
    > all cases---4b, 42, 40, 43, 49, 41,
    > 4b, 4b, 4e. Checked three comps, with
    > similar results. All Linux-generated UUID (boot_id)
    > that I see in internet has '4' in this
    > half-byte.

    This appears to be deliberate. From drivers/char/random.c:

    void generate_random_uuid(unsigned char uuid_out[16])
    {
    get_random_bytes(uuid_out, 16);
    /* Set UUID version to 4 --- truly random generation */
    uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
    /* Set the UUID variant to DCE */
    uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
    }
    EXPORT_SYMBOL(generate_random_uuid);

    Version 4 UUIDs and the format used are described at
    http://en.wikipedia.org/wiki/Universally_Unique_Identifier

    Ian.

    --
    Ian Campbell
    Current Noise: Jesu - Your Path To Divinity

    Build a system that even a fool can use and only a fool will want to use it.



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