Information Technology Reference
In-Depth Information
well. Hence the PSE generates the modulus
n
, the public exponent
e
,and
the private exponent
d
. In the generation process, there is no need for the
private exponent
d
. This parameter is only needed for later disclosure of the
pseudonym.
UID
||
Data
||
PAD
e
n
D
EID
e
n
Fig. 2.
Generation of a Unique Pseudonym
2. The unique identifier (
UID
) is concatenated with some additional data
(
Data
) and some padding (
PAD
) and is finally encrypted with the public-
key (
e, n
). In the remainder of this paper we will call this block holding the
user identifier the UID-Block.
The data field has to contain a serial-number of the pseudonym, which
has to be incremented automatically each time a pseudonym is generated
by the PSE. If a user employs different PSEs, the data-field has to store a
device identifier as well. By this, we can guarantee, that different devices
generate different pseudonyms.
Additionally, the data field may contain the (unique) identifier of the
Application (
AID
) requesting the pseudonym. By this, the user holds differ-
ent pseudonyms for different applications and there is no way for correlating
data of different applications. If these application-specific pseudonyms are
used, the PSE has to store the pseudonym along with the
AID
for later
usage.
3. The result of this encryption process, the so called encrypted ID (
EID
), is
concatenated with the public-key. In case of RSA this results in
EID
||
e
||
n
,
which forms the unique and highly random pseudonym
P
=
EID
n
.
The proof of uniqueness is given in the next section. Concerning the
randomness of the pseudonym, it is obvious that the second half is com-
pletely random, because we chose
e
,
p
1
and
p
2
(and hence
n
)atrandom.
The first half is an encrypted block. Since the key used for encryption was
chosen at random, the encryption function works as a strong pseudo-random
function.
||
e
||
2.1
Proof of Uniqueness
The proof of uniqueness of the generated pseudonyms is straight forward and is
based on the following facts:
