Conventional Encryption Principles
what is Conventional Encryption Principles
Symmetric encryption is also referred to as conventional encryption or single-key encryption. It was the only
type of encryption in use prior to the development of public-key encryption. It
remains by far the most widely used of the two types of encryption.
A symmetric encryption
scheme has five ingredients:
Plain text: This is the Original intelligible message or data that is
fed in to the algorithm as input.
Encryption Algorithm: The encryption algorithm performs various
substitutions and transformation on the plain text to convert it into
ciphertext.
Secret Key: The secret key is also input to the encryption algorithm.
The key is a value independent of the plain text. The algorithm will produce a
different output depending on the specific key being used at the time. The
exact substitutions and transformations performed by the algorithm depend on
the key.
Ciphertext: This is the scrambled message produced as
output. It depends on the plain text and the secret key. For a given message,
two different keys will produce different ciphertexts. The ciphertext is an
apparently random stream of data and, as it stands, is unintelligible.
Decryption Algorithm: This is essentially the encryption algorithm run in
reverse. It takes the ciphertext and the secret key as the input and produces
the original plain text.
Two main requirements are needed for secure use of conventional encryption:
(i).
A strong encryption algorithm is needed. It is desirable that the algorithm
should be in such a way that, even the attacker who knows the algorithm and has
access to one or more cipher texts would be unable to decipher the ciphertext
or figure out the key.
(ii).The
secret key must be distributed among the sender and receiver in a very secured
way. If in any way the key is discovered and with the knowledge of algorithm,
all communication using this key is readable.
The
important point is that the security of conventional encryption depends on the
secrecy of the key, not the secrecy of the algorithm i.e. it is not necessary
to keep the algorithm secret, but only the key is to be kept secret. This
feature that algorithm need not be kept secret made it feasible for wide spread
use and enabled manufacturers develop low cost chip implementation of data
encryption algorithms. With the use of conventional algorithm, the principal
security problem is maintaining the secrecy of the key.
Cryptography
A
cipher is a secret method of writing, as by code. Cryptography, in a very broad
sense, is the study of techniques related to aspects of information security.
Hence cryptography is concerned with the writing (ciphering or encoding) and
deciphering (decoding) of messages in secret code. Cryptographic systems are
classified along three independent dimensions:
1.
The type of operations used for performing plaintext to ciphertext All the
encryption algorithms make use of two general principles; substitution and
transposition through which plaintext elements are rearranged. Important thing
is that no information should be lost.
2.
The number of keys used If single key is used by both sender and receiver, it
is called symmetric, single-key, secret-key or conventional encryption. If
sender and receiver each use a different key, then it is called asymmetric, two-key
or public-key encryption.
3.
The way in which plaintext is processed A block cipher process the input as
blocks of elements and generated an output block for each input block. Stream
cipher processes the input elements continuously, producing output one element
at a time as it goes along.
Cryptanalysis
The
process of attempting to discover the plaintext or key is known as
cryptanalysis. It is very difficult when only the ciphertext is available to
the attacker as in some cases even the encryption algorithm is not known. The
most common attack under these circumstances is brute-force approach of trying
all the possible keys. This attack is made impractical when the key size is
considerably large. The table below gives an idea on types of attacks on
encrypted messages.
Cryptology
covers both cryptography and cryptanalysis. Cryptology is a constantly evolving
science; ciphers are invented and, given time, are almost certainly breakable.
Cryptanalysis is the best way to understand the subject of cryptology.
Cryptographers are constantly searching for the perfect security system, a
system that is both fast and hard and a system that encrypts quickly but is
hard or impossible to break. Cryptanalysts are always looking for ways to break
the security provided by a cryptographic system, mostly though mathematical
understanding of the cipher structure.
Cryptography
can be defined as the conversion of data into a scrambled code that can be
deciphered and sent across a public or a private network.
A
Known-plaintext attack is an attack in which an individual has the plaintext
samples and its encrypted version (ciphertext) thereby allowing him to use both
to reveal further secret information like the key
A
Chosen- plaintext attack involves the cryptanalyst be able to define his own
plaintext, feed it into the cipher and analyze the resulting ciphertext.
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