Cryptography is the art and science of secure communication. “kryptos” is Greek word, which means ‘secret writing’.
Cryptography is not
a modern invention nor because of dawn of computers, in fact its almost 3 or 4
thousand years old practice of communicating securely. Kings as part of warfare
or strategy were sending messages from one king to another in secret writing so
that his\her enemy shouldn’t able to read the messages by capturing the
messenger. Secret writing like, write message in hidden ink, substitution cipher (with shift of 3 A will be C, C will F)
etc.
Almost all modern
encryption\decryption of data, whether it’s WIRED (web, file system, messages) or
WIRELESS (cell, sensors) done by three ways:
- Symmetric key
- Asymmetric key
- Mix of Symmetric
and Asymmetric keys
Symmetric key cryptography
Symmetric
(reflection or mirror) uses a single secret\shared key for both encryption and
decryption. In this type of crypto both sender and receiver should know the
secret key up front.
Sender encrypts the
message using secret key, message transferred over network, Receiver decrypts
the message using same secret key used for encryption.
pic courtesy Oracle corp.
The main drawback
of shared-key crypto is the difficulty of securing the secret-key, which needed
by both sender and receiver, so high chances of leaking the key. It’s called key distribution problem.
Asymmetric key cryptography
Also called
public-key or public private key cryptography. Due to the drawbacks of
symmetric key, made the way to invention of asymmetric key.
Public-key
cryptography, proposed by Diffie and Hellman in 1976, is the idea of having two
separate keys, a public key for encryption of a message and a secret key for
its decryption; a party can privately construct the two keys and then make the
encryption key public without thereby revealing the decryption key.
Subsequently, anyone can encrypt messages intended for the creator of the keys,
but only the creator can decrypt. The first realization of this idea was due to
Rivest, Shamir, and Adleman in 1978.
At the heart of RSA – public key crypto
is depend upon the properties of the product of two large prime numbers. This
algorithm is based on some principles from Number theory, which states that
determining the prime factors of a large number is extremely difficult.
pic courtesy Wiki
Differences
Symmetric key
|
Asymmetric key
|
Encrypts 256 bits
|
Encrypts 1024
bits or 2048 bits
|
The size of
ciphered text is less or equal to plain text
|
The size of
ciphered text is heavy
|
Less computing
power
|
Need lot of
computing power
|
Used : client and
server
|
Used for: digital
signature, session key …
|
DES, AES
algorithm
|
RSA algorithm
|
Same key for encrypt
and decrypt
|
Public key for
encrypt and private key for decrypt
|
Cryptanalysis is the art and science of breaking
the encrypted codes that are created by applying some cryptographic algorithms.
