- Cryptography is a secure communication technique which allows only the sender and recipient of a message to view its contents. Cryptography is primarily used as a tool to protect national secrets and strategies. In simple words, it the art and science of using mathematics to encrypt and decrypt data.
- A cipher is a mathematical function used in the encryption and decryption process. Cryptography hides sensitive information away from the peeping eyes of third parties. The most common use of cryptography is to encrypt and decrypt email or plain-text messages when transmitting electronic data.
- Data can be read and understood without any special measures is called plaintext or clear text. Data which requires some special function to be performed on it before it can be read and understood is called cipher text. A cryptographic algorithm, plus all possible keys and all the protocols that make it work comprise a cryptosystem.
Features of Cryptography:
- Confidentiality is used to keep the content of information secret from unauthorized persons.
- In integrity there is no modification or addition in information between sender and intended receiver.
- Non-repudiation prevents someone from denying previous commitments or actions.
- Authentication is the process of verification of the identity of a user or information. This function applies to both the entities and the information itself.
keys:
A key is a value that works with a cryptographic algorithm to produce a specific cipher text. Keys are basically very very big numbers. Key size is measured in bits.
Ex. 04 CE D7 61 49 49 FD 4B 35 8B 1B 86 BC A3 C5 BC D8 20 6E 31 17 2D 92 8A B7 34 F4 DB 11 70 4E 49 16 61 FC AE FA 7F BA 6F 0C 05 53 74 C6 79 7F 81 12 8A F7 E2 5E 6C F5 FA 10 69 6B 67 D9 D5 96 51 B0
Type of cryptography:
1. Symmetric Cryptography:
In conventional cryptography, also called secret key or symmetric key encryption, the same key is used both for encryption and decryption. In symmetric cryptography size of cipher text is the same or smaller than the original plain text. This process is very fast. The length of key used is 128 or 256 bits The Mathematical Representation is as follows:
P = D (K, E(P)) where
K - encryption and decryption key P – plain text D – Decryption E(P) – Encryption of plain tex
2. Asymmetric Cryptography:
Public key cryptography is an asymmetric scheme that uses a pairs of keys: a public key, which encrypts data, and a corresponding private key, or secret for decryption. The size of cipher text is the same or larger than the original plain text in asymmetric cryptography. The encryption process is slow. In this cryptography, length of key used is 2048 or higher.
The Mathematical Representation is as follows:
P = D(Kd, E (Ke,P))
where Ke – encryption key
Kd – decryption key
D – Decryption
E(Ke, P) – Encryption of plain text using encryption key Ke
P – plain text
Hash Function:
A one-way hash function takes variable-length input- say a message of any length- and produces a fixed-length output; say, 160-bits. The hash function ensures that, if the information is changed in any way –even by just one bit- an entirely different output value is produced.