Cryptography
When we want to encrypt some information so that only the actual receiver can read the information, we are using the cryptography.To encrypt some text we need the following things.
- Cypher - A cipher (or cypher) is a pair of algorithms which create the encryption and the reversing decryption
- Key - A phrase which will an input to the Cypher. Algorithms will use this key to encrypt/decrypt the text. If the algorithms will work without the key, then it is useless. Anyone who knows which algorithms are being used to encrypt/decrypt, will be able to encrypt/decrypt the information. So key is important. Depending upon the keys being used for encryption and decryption, we have two variants of cryptography.
- Symmetric-Key Cryptography - In this the same key is used for encryption as well as decryption algorithm. Data Encryption Standard(DES) and Advanced Encryption Standard(AES) are tho such algorithms.
- Public-Key Cryptography - Disadvantage with the Symmetric-key cryptography is that the 'key' will be shared between sender and receiver. So the key will have to send from the sender to the receiver. Now someone can steal this key while it is being sent.
In Public-key cryptography key-pairs are used. Let's say A wants to send some message to B. A will have two keys one private and other public. Similarly B will have pair of keys - private and public. The private keys are 'private' so only A will know his private key and only B will know his private key. Public keys are for public so everybody knows A's and B's public keys.
If A wants to send some message to B, then A will encrypt the message from B's public key. Now this encrypted message can be decrypted only from B's private key. This private key is known to B only, so only B can decrypt this message. Similarly if B wants to send some message to A, B will encrypt the message from A's public key.
RSA and DSA are two such algorithms.
Digital Signatures
Digital Certificates
SSL/TLS
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