lationship between ciphers, keys, transposition, and substitution [ 10].
Concealment of the key is of primary importance in data encryption.
Modern digital communications systems employ encryption methods based on numeric key systems. In digital systems the encrypting
and decrypting algorithms are generally referred to as ciphers. The
key is a number that is used in an algorithmic transformation of the
plaintext or ciphertext. As seen in the exclusive-or example, both
encryption and decryption use the key on the working matter (
plaintext or ciphertext). Current key cryptography is broken down into two
categories based on usage scope. These are symmetric-key and asymmetric-key cryptography. In symmetric-key the sender and receiver
Encryption of Digital Data for Security utilize the same algorithm and key for encryption and decryption. In
Modern ciphers are built by component ciphers, including the rota- asymmetric-key encryption the concepts of public and private keys
tion cipher, the XOR cipher, expansion permutation, as well as oth- come into play. This arrangement provides a method for key security.
ers [ 4]. In computing, encryption is carried out at the bit level, and The designated receiver holds a private key, while the public key is
the digital techniques used to manipulate bits form the basis of cur- available to all. The two keys are quantitatively distinct [ 4].
rent secure communications systems. There are several examples of modern encryption systems based
The goals in digital encryption are no different than those of his- on symmetric-key methods. Let us begin by discussing the Data
torical encryption schemes. The difference is found in the methods, Encryption Standard (DES). This is a symmetric-key system that has
not the objectives. Secrecy of the message and keys are of paramount formed the basis for certain methodologies, including Kerberos 4.0
importance in any system, whether they are on parchment paper or [ 1]. Though the DES process commences with a 64-bit input key, the
in an electronic or optical format. Modern communication systems effective key length is 56 bits, since for every byte of input data, the
utilize software protocols to carry out encryption within a hierarchi- least significant bit is used for parity check. The value of the parity
cal protocol suite, such as TCP/IP. The process remains practically bit is determined so as to make an odd number of 1’s in each byte of
transparent to the sender and receiver. information [ 7]. DES consists of 16 rounds of encryption. A round of
Thus far, for illustrative purposes, we have discussed manipulation encryption is a process performed upon the data, such as XOR or
at the character, letter, or symbol-level. Computing technology takes en- permutation. DES begins by splitting the 64 bits of data into two 32-
cryption to a much lower, and thus, more powerful level. Digital elec- bit sections. Then, the 16 rounds of encryption processes are per-
tronic and optical systems employ cipher-based encryption methods at formed on the data before it is eventually reassembled into an output
a basal level. These systems lend themselves very well to enciphering of 64 bits. At the core of the DES process is the “DES function.” This
schemes, as bit manipulation affords an excellent facility of positional is a process that uses a 48-bit key on each 32-bit section, and carries
alteration, as well as the important component of parity checking. out various encryption/manipulation operations on the data [ 4].
Digital data and information, including video, audio, and text, can In response to criticism that DES’s key of 64 bits was too short
be separated into groups, or blocks, of bits, and then manipulated for and therefore not secure enough, Triple DES (3DES) was developed.
encryption by such methods as XOR (exclusive OR), encoding- Triple DES seeks to allay the short-key concern of DES by increasing
decoding, and rotation [ 4]. As an example, let us examine the basics the key length. The process “stacks” three DES processes on top of
of the XOR method. Here, a group of bits (e.g., a byte) of the data is each other in an encrypt-decrypt-encrypt fashion on the encryption
compared to a digital key, and the exclusive-or operation is per- side, and in a decrypt-encrypt-decrypt fashion on the decryption
formed on the two to produce an encrypted result. Figure 2 illus- side. Because the process of 3DES was shown to be time-consuming
trates the process. When the exclusive-or operation is performed on and burdensome with regards to resources, the Advanced Encryption
the plaintext and key, the ciphertext emerges and is sent. The Standard (AES) was developed. This standard is rendered in three
receiver performs the exclusive-or operation on the ciphertext and basic versions that vary in key-length (128-, 192-, or 256-bit), as well
the same key, and the original plaintext is reproduced [ 4]. as the number of encryption rounds. AES is one of the more popular
Simple manipulation techniques such as these illustrate the potential methods employed today. A given key in this process is basically an
power of digital encryption. Over the decades, discoveries in number the- altered version of the prior key in the encryption stack [ 4].
ory and computer science have broadened the scope of implementations Asymmetric-key cryptography uses a set of two distinct keys in
of ciphers in computing. The basis of computer data security is the re- the encryption and decryption processes. Encompassing number
theory and modular arithmetic,
much of the mathematical concept
of public and private key encryption
is based on “Fermat’s little theorem.”
Fermat’s little theorem states that if
p is a prime number and not a fac-
tor of a, then when a is raised to the
power of p – 1 and that result divided
Figure 2: The XOR process for encryption. by p, there will be a remainder of 1
enciphered. For the sake of simplicity, let us use the following
monoalphabetic cipher key with a shift of +3:
a=d, b=e, c=f, d=g, e=h, f=i, g=j, h=k, i=l, j=m, k=n,
l=o, m=p, n=q, o=r, p=s, q=t, r=u, s=v, t= w, u=x, v=y,
w=z, x=a, y=b, z=c
Assuming that spaces are unencrypted, the resulting encrypted message is jdgv dhloeuhw. On the receiving side, the inverse of the
encryption algorithm is carried out by first deciphering with the key.
Then, the result is decoded to produce the original plaintext.