Lec 15- General Cryptography Concepts

Cryptography defined

Cryptology is transformation from plaintext to ciphertext.

Cryptanalysis is breaking ciphertext to reterieve plaintext.

Cryptography is to scramble plaintext in such a way that intruder is not able view, interpret original message. Objective of cryptography is to ensure Confidentiality, Integrity, Authentication and Non-repudiation.

First cipher used was ceaser cipher.

Symmetric cryptography

Encryption and decryption keys are same. There are two types of symmetric algorithms:

1- Stream ciphers, like RC2,4,5,6 encrypt data in the form of streams. Data encrypted and decrypted on subsequent indexes is dependent on data at earlier indexes.

2- Block ciphers, AES 128,192,256 data is encrypted, decrypted in blocks independently.

Symmetric algorithms are effecient.

Asymmetric cryptography

Encryption and decryption keys are different. RSA algorithm, eliptic curve, Deffi Helman, Elgamal algorithm.

Asymmetric key algorithms are 1000 times slow as compared to symmetric algorithms. are used for digital signatures and key exchange.


Hashing is used for ensuring message integrity. Message is passed through hashing algorithm to generate fixed length number. Exmaple: MD5, SHA-512.



Confidentiality is art of hiding information so that intruder does not see it.


Integrity is making sure that intruder does not change message.


Availability is making sure things that are intended, should be available.


Access to objects should be authenticated. Intruder should not be able get into systems without authentication.

 Non repudiation

Sender of message can not deny sent message.

Trusted Platform Module TPM

Trusted Platform Module is micro controller chip over that is responsible for generating secure keys for and secure random number generation. Bitlocker use keys generated by TPM Module.


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