IEEE Consumer Electronics Magazine - October 2015 - 59

Message
UTF-8 in Hex
Original Message
Alice's Key
Encrypt for Bob
Bob's Key
Encrypt to Alice
Decrypt by Alice
Resent to Bob
Decrypt by Bob
Final Message
Final Message UTF-8
Recovered Message

i
79
10011110
11011011
01000101
00110000
01110101
11011011
10101110
00110000
10011110
79
i

P
50
00001010
01010010
01011000
11110100
10101100
01010010
11111110
11110100
00001010
50
P

a
61
10000110
10001010
00001100
00011100
00010000
10001010
10011010
00011100
10000110
61
a

d
64
00100110
11100111
11000001
01101001
10101000
11100111
01001111
01101001
00100110
64
d

Printable "iPad"
Little Endian
0xDB4A51E7
Bit-by-Bit XOR
0x0C2F8396
Bit-by-Bit XOR
0xDB4A51E7
Bit-by-Bit XOR
0x0C2F8396
Bit-by-Bit XOR
"iPad"

FIGURE 4. An example of using digital keys to encrypt and decrypt data.

Is access to my devices secure from unauthorized agents?
(Key generation)
▼ Is my data safe from eavesdropping? (Encryption)
▼ Is my data believed by the receiver? (Authentication)
▼ Can I be followed? (Privacy.)
Any communication can be intercepted. This is true for
wired or wireless connections. A lot of work has been done in
the past few decades to invent and extend methods to make
communications secure enough for end users.
▼

KEY GENERATION
A crucial early advance was to find a way for communicators
to create and exchange secrets that were carried over a media
that could be intercepted. The most widely used method is
based on public key cryptography by Diffie, Hellman, and
Merkel [53]. Methods derived from this are used to generate
encryption keys and authentication keys for a variety of systems, including point-to-point radios (like 802.11, 802.15.4,
and Bluetooth) and system-to-system communications over
the Internet.
Let us illustrate public key cryptography with a physical
analogy: assume a postal system that can be intercepted. Suppose that an agent (Alice) has a box with room for two padlocks. She composes a secret, inserts it into the box, padlocks
it with her lock, and ships the box to a second agent (Bob).
Interceptors can get their hands on the box, but we assume
that they are not capable of breaking Alice's padlock. Bob
cannot open the box either, but he can put his own second
padlock on the box. He can then send it back to Alice. She
can remove her own padlock and send it back to Bob-with
his padlock still attached. He can unlock the second padlock
with his own key and recover the secret (Figure 3).

ENCRYPTION
In digital communications, the keys are long strings of bits that
are used to make Exclusive OR (XOR) combinations with the
original plain text data, on a bit-by-bit basis. If the receiving
device has the same keys, reapplying XOR operation on a

bit-by-bit basis recovers the original plain text. In modern systems, these keys are 128 bits long.
Figure 4 shows how a digital key might be used to encrypt
and decrypt a message. The keys are shortened and this illustration only uses 32 bits. Each character is shown printable
and represented in a two-digit hexadecimal notation, in bigendian order per character. The two public keys for Bob and
Alice are randomly generated, but used twice, analogous to
their use in Figure 3.
The methods must also be careful to avoid exposing
known plain text, because if they do then hackers can simply
apply an XOR with known plain text and recover the keys.
Modern key generation methods go to a lot of effort to avoid
exposing known plain text. In these methods, a final step is
for each agent to independently derive the keys, and then
encrypt some exchanged data so that each agent can confirm
that the other agent has a matching key.

Open Mobile Alliance has
standardized a method for
encoding these applications
over CoAP.

AUTHENTICATION
These methods also combine plain text with the primary keys
through one-way mathematical functions to generate shorter
authentication keys. In the above connectivity examples,
octets were added for authentication, so that the receivers can
trust the sources of the data.
These security methods can and should be used in two places:
1) device-to-device to secure each connection
2) end-to-end to secure each relationship.
october 2015

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IEEE ConsumEr ElECtronICs magazInE

59
Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - October 2015
