INTERODUCTION TO CRYPTOGRAPHY. b y Muktadiur Rahman May 06, 2010. Contents. Introduction Basic Terms Cryptographic Services Symmetric Algorithms Asymmetric Algorithms Hashing Algorithms Digital Signature Public Key Infrastructure Cryptanalysis Attacks. Introduction.
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May 06, 2010
Public Key Infrastructure
Plaintext – the original intelligible message
Ciphertext – the transformed message
Chiper–the algorithm that does the encryption
Key – some critical information used by the cipher, known only to the sender receiver.
Keyspace– Total number of possible values of keys in a crypto algorithm
Cryptosystem – The combination of algorithm, key, and key management functions used to perform cryptographic operations
Cryptology - both cryptography and cryptanalysis
Encryption: the process of converting plaintext to cipher text using a cipher and a key
Decryption: the process of converting cipher text to plaintext
Confidentiality: To help protect a user's identity or data from being read.
Data integrity: To help protect data from being changed.
Authentication: To ensure that data originates from a particular party.
Non-repudiation: To prevent a particular party from denying that they sent a message.
In asymmetric cryptography, each user has two keys: a public key and a private key. The public key is made public. For example, it may be published on a Web site. The private key must be kept secret. It is never shared with anyone. Their main use is in solving the key exchange problem for symmetric cryptography
Asymmetric algorithms tend to be very inefficient cause it is very slow, about 100 times slower than DES
Cryptographic hashing functions are used to ensure the integrity of data. Cryptographic hashing functions are sometimes called cryptographic checksums or integrity checksums.
Hashing functions are also used for digital signatures
Public key encryption enabled the development of the technology of digital signatures. Digital signatures are somewhat analogous to traditional handwritten signatures. Digital signatures are strongly bound to the document, but weakly bound to the individual. A digital signature is computed, in part, using the contents of the document being signed.
A PKI (public key infrastructure) enables users of a basically unsecure public network such as the Internet to securely and privately exchange data and money through the use of a public and a private cryptographic key pair that is obtained and shared through a trusted authority. The public key infrastructure provides for a digital certificate that can identify an individual or an organization and directory services that can store and, when necessary, revoke the certificates.