Cryptography Reference
In-Depth Information
At Paris, just after dark one gusty evening in the autumn
of 18, I was enjoying the twofold luxury of meditation
and a meerschaum, in company with my friend C. Au-
guste Dupin, in his little back library, or book-closet, au
troisime, No. 33 Rue Donot, Faubourg St. Germain. For
one hour at least we had maintained a profound silence;
while each, to any casual observer, might have seemed in-
tently and exclusively occupied with the curling eddies of
smoke that oppressed the atmosphere of the chamber. For
myself, however, I was mentally discussing certain topics
which had formed matter for conversation between us at
an earlier period of the evening; Imean the affair of the Rue
Morgue, and the mystery attending the murder of Marie
Rogt. I looked on it, therefore, as something of a coinci-
dence, when the door of our apartment was thrown open
and admitted our old acquaintance, Monsieur G, the Pre-
fect of the Parisian police.
[Poe44]
The algorithm used the original order as the canonical order for
the letters in each word and then hid information in the order of the
n −
2 interior letters of every
n
-letter word.
13.9 Adding Extra Packets
Another way to scramble the order is to add fake packets. Ron Rivest
suggested this idea as one way to evade a ban on cryptography.
[Riv98] He suggested letting every packet fly in the clear with a digital
signature attached. Valid packets come with valid signatures, while
invalid packets come with invalid signatures.
Rivest suggested using keyed message authentication codes gen-
erated by hash functions.
If
x
is the message, then the signa-
ture consisted of
f
(
kx
),where
k
is a key known only to those who
f
(
x
) be some bad signature-generating
function, perhaps a random number generator. Let the message
be
can read the message. Let
{x
1
,x
2
,...,x
n
}
. Rivest called these the
wheat
.Letthe
chaff
, random numbers of the correct size. The mes-
sage consists of pairs like (
x
1
,f
(
kx
1
)) mixed in with distractions like
(
r
i
,f
(
r
i
)).
Many standard digital signature algorithms can also be used if we
relax the notion that the signatures can tested by anyone with access
to a public key. If the verification key is kept secret, only the sender
and any receiver can tell the wheat from the chaff. Traditional public
be
{r
1
,...,r
k
}
