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Cryptography is the study of transforming information in order to make it secure from unintended recipients or use. When information is transformed from a useful form of understanding to a useless form of understanding, this is called encryption. When the information is reverted back into a useful form, it is called decryption. Intended recipients or authorized use of the information is determined by whether the user has a knowledge of a certain piece of the secret. Only users with the secret knowledge can transform the useless information back into its useful form. The secret knowledge is commonly called the key, though the secret knowledge may include the entire process or algorithm that is used in the encryption/decryption. The information in its useful form is called plaintext; in its useless form it is called ciphertext. The algorithm used for encryption and decryption is called a cipher (or cypher).
Common goals in cryptography
In essence, cryptography concerns four main goals. They are:
- message confidentiality: Only an authorized recipient should be able to extract the contents of the message from its encrypted form.
- message integrity: The recipient should be able to determine if the message has been altered during transmission.
- sender authentication: The recipient should be able to identify the sender, and verify that the purported sender is who they claim to be.
- sender non-repudiation: The sender should not be able to deny sending the message.
Not all cryptographic systems achieve all of the above goals. Some applications of cryptography have different goals; for example some situations require repudiation where a participant can plausibly deny that they are a sender or receiver of a message.
Important Uses of Cryptography:
- Protect confidentiality of message (Achieved with Encryption Algorithms)
- Provide identity for authentication (Achieved with Asymmetric Encryption Algorithms, digital signature algorithms)
- Verify information to check message integrity (Achieved with hash functions)
Common forms of cryptography
Cryptography involves all legitimate users of information having the keys required to access that information.
- If the sender and recipient must have the same key in order to encode or decode the protected information, then the cipher is a symmetric key cipher since everyone uses the same key for the same message. The main problem is that the secret key must somehow be given to both the sender and recipient privately. For this reason, symmetric key ciphers are also called private key ciphers.
- If the sender and recipient have different keys respective to the communication roles they play, then the cipher is an asymmetric key cipher as different keys exist for encoding and decoding the same message. It is also called public key encryption as the user publicly distributes one of the keys without a care for secrecy. In the case of confidential messages to the user, they distribute the encryption key. In the case of authentication of the user, they distribute the decryption key. Asymmetric encryption relies on the fact that possession of one key will not reveal the other.
Types of Cryptography:
- Secret key cryptography (Both parties know the same secreat key. Uses symetric encryption)
- Public key cryptography (Both parties have 2 different keys,Public key for encryption and Private key for decryption.
In Reversible public key algorithms, Data encrypted with private key can be decrypted with public key.Uses asymetric encryption)