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8.2.2 A Study of Encryption Algorithms and Hashing Functions
he encryption algorithm is one of the most critical aspects of the cryptosystem. he strength
provided to protected data is based on the strength of the underlying encryption algorithm and
the key and its secrecy. he source of the most accepted encryption algorithms of today are not
secret and are usually open to the public domain; this is because it is widely accepted that the key
is the only element * of the cryptosystem that needs to be kept conidential. he most accepted
encryption algorithms undergo rigorous testing by cryptanalysts all over the world, and only after
it is proven that the algorithm cannot be broken, are they accepted as industry standard. hese
encryption algorithms and one-way hash functions have evolved over time. We will now delve
into some of the popular encryption algorithms and one-way hash functions, their evolution, their
implementation, and their characteristics:
AES—advanced encryption standard
DES/3DES—data encryption standard
RC4
Blowish
RSA
PGP
MD5
SHA
8.2.2.1 DES/Triple DES
Data encryption standard (DES) was created by IBM in 1974 for a project called Lucifer. DES
came to become an industry accepted standard because the National Bureau of Standard, now
known as National Institute of Standards and Technology (NIST), had a need for an encryption
algorithm for government use and for the protection of other classiied information. Subsequently,
DES was approved as a federal standard in the year 1976. DES was an extremely popular standard
for commercial implementations, until it was broken by a brute-force attack in the year 1998,
which necessitated the need for a new encryption standard.
DES is a symmetric block cipher. It works on blocks of 64 bits, where 64-bit blocks of cleartext
are converted to 64-bit blocks of ciphertext. he key length of the DES is 64 bits, where 56 bits is
the size of the true key length and 8 bits are used for parity. DES is a substitution and transposi-
tion cipher, where blocks are subjected to 16 rounds of substitution and transposition.
DES was replaced later by an algorithm developed on its foundations, known as the Triple
DES or 3DES. Triple DES was developed to add the element of greater key size to DES, without
afecting the need to develop a totally new encryption algorithm as a standard. Triple DES uses
three DES keys to encrypt and decrypt the data, and the blocks are subjected to 48 rounds of
substitutions and transpositions, thereby adding the resistance to the encrypted data. However,
the encryption and decryption process with Triple DES takes thrice the time as compared to the
process of encrypting data with DES. Apart from these diferences, the main diference between
DES and Triple DES is with the keys. here are three types of key options that are available for
* Please refer to Kerckhof's principle—http://en.wikipedia.org/wiki/Kerckhofs%27_principle.
DES brute-force attack: http://www.interhack.net/pubs/des-key-crack/.
Parity bits are those that are used to ensure that the number of bits in a value set to 1 is odd or even. Parity bits
are used as error correction mechanisms.
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