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NSA assure all parties that this back door would only be used in a
concrete case of suspicion of capital criminal actions, and even then
only with prior approval from a judge. Two questions arise:
Is this back door really secure? That is, can it be exploited by third
parties to read the data?
Is the statement by the U.S. government and NSA to be trusted?
Introduction to Cryptography G-3
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Encryption Procedures
Symmetrical Procedures (Private Key) (Continued)
ROT13
A (very weak) procedure by which every letter is replaced by the letter
that is 13 places away in the alphabet. Because the alphabet contains
26 letters, if the process is applied twice, the original text is returned.
Numbers and special characters are not changed.
ROT13 is used primarily by USENET groups to mask statements that
are offensive or insulting: Read at your own risk!
The following text is ROT13:
sun% tr A-Za-z N-Za-Mn-za-m
Crypted
The key length is irrelevant, because the key (13) is known. The
algorithm itself is trivial. Protection against reading by third parties is
also not assured.
Asymmetric Procedures (Public Key)
General
Here two keys are used. One key is used to encrypt, the other to
decrypt. Although both keys obviously are related, it is not possible
(in relatively finite time) to determine the content of one key, even
with full knowledge of the other key.
G-4 Solaris Network Security
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Encryption Procedures
Asymmetric Procedures (Public Key) (Continued)
Diffie-Hellman
This is an asymmetrical procedure that (in secure RPC) uses 192-bit
keys to exchange DES keys.
RSA (Rivest, Shamir, and Adleman)
This is a procedure (Pretty Good Privacy) with primarily a 51-bit key.
RSA provides additional authentication possibilities. PGP is based on
the RSA algorithms.
Other Procedures
Cipher Block Chain
The basic procedure is again a symmetrical procedure: however, here
the preceding block is used to encrypt a block with a (symmetrically
reversible) quasi to pre-encrypt. XOR is often used for this. PROBLEM:
For the first block there is no (already encrypted) block available, so a
substitute word must be introduced between the partners. This value
is known as the Initial Vector (IV).
One-Time Password
Here are more uses, which points out one common fact: each
password is used once and once only. Exemplary algorithms and
implementations follow.
Introduction to Cryptography G-5
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Encryption Procedures
Other Procedures (Continued)
The passwords are taken from a list known to both partners. (This
is a procedure that banks use to transmit with Datex-J (Btx).
The passwords are generated using an algorithm known to both
partners. Here a question (challenge) is presented to the partner:
both calculate the answer (which is dependent again upon
mutually known information). The decisive part is that neither the
key nor the algorithm can be determined once you know the
answer to the challenge.
The challenge consists of a time (or derivative information)> This
makes the explicit challenge unnecessary; the attacker (intruder)
knows only the answer. He does not know the challenge, and
cannot therefore derive the key or the algorithm.
FireWall-1 Authentication
The communication between two FireWall-1 systems is based on One-
Time Passwords, which are derived from each other. To this is added
an initial password (a seed) used to hinder password duplication.
S/Key
This is a challenge and response algorithm, which presents the
challenges not randomly, but from a list. The user is in the position to
print off a list of future passwords without knowing the algorithm.
Note The author sees this print function as a potential weakness,
because the possibility exists that after one successful authentication,
an intruder could then successfully pick up the remaining passwords.
The software itself indicates this risk that this edition is not to be
used when one is remotely connected (network or dial-up). Does that
influence a cracker ?
G-6 Solaris Network Security
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Weaknesses of Encryption Technology.
The following points were extracted from he book PGP: Pretty Good
Privacy.
No protection exists for:
Nonencrypted documents.
Against theft of keys.
Against destruction.
Error-prone or buggy encryption software.
Data passed on by traitors.
Keys that are pulled just by being used.
This point should be considered more closely, because it is more
complicated than the other cases:
Scenario: Bob loves Mary, who is married to Tom.
Bob sends an encrypted message to a fourth person, Joe. Days later
Tom is murdered. Later, Bob and Joe again exchange encrypted data.
An observer could come to believe (without the original data it is hard
to disprove) that Bob had asked Joe to kill Tom (first message). Joe had
done this, informed his boss (second message), and had received a
commensurate reward.
Introduction to Cryptography G-7
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Encryption and the Law
Note The statements provided here are not legally binding; the
author and the organizations of Sun Microsystems disclaim all
responsibility for damages and costs related to use of this information.
The author is not in a position to cite all relevant laws, so examples
will be used to indicate the tone.
Trade Limitations
United States of America
The export of encryption technology from the U.S.A. is considerably
encumbered by export controls. The decisive factor for the procedure
is the ability to encrypt data. For purely authentication uses,
exceptions are possible.
The aforementioned constraints apply to concrete implementations,
(whether in software or hardware) such as the DES chip, but do not
apply to the algorithms. Construction is relatively not problematic, but
if assembled overseas and reintroduced into the U.S.A., the laws apply
again.
In the book PGP: Pretty Good Privacy, the possible penalty for a
transgression against the export laws would be a fine of up to
$1,000,000, up to ten years imprisonment, or any combination of the
two.
Note Please pay attention to the U.S. export laws, which also apply
when the data comes from an FTP server on American soil. Inform
yourself (through read-me files) where the restrictions (and often
alternatives) are given.
G-8 Solaris Network Security
Copyright 1997 Sun Microsystems, Inc. All Rights Reserved. SunService August 1996
G
Encryption and the Law
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