This document discusses the importance of cryptography and PKI for ensuring security, privacy, and authentication in digital communications. It addresses the three main goals of cryptography - confidentiality, integrity, and availability. The document then provides an overview of cryptographic algorithms, including symmetric and asymmetric encryption as well as hash functions. It also discusses common cryptanalytic attacks and how the strength of encryption increases exponentially with longer key sizes, making brute-force attacks infeasible for sufficiently long keys.

2. Why pki

3.  Preserving authorized restrictions on
information access and disclosure, including
means for protecting personal privacy and
proprietary information. A loss of
confidentiality is the unauthorized disclosure
of information.

4.  Guarding against improper information
modification or destruction, including
ensuring information nonrepudiation and
authenticity. A loss of integrity is the
unauthorized modification or destruction of
information.

5.  Ensuring timely and reliable access to and use
of information. A loss of availability is the
disruption of access to or use of information
or an information system.
CIA triad to define security objectives.

7.  Cryptography is the science of writing in secret
code.
 The first documented use of cryptography in
writing dates back to circa 1900 B.C.
 New forms of cryptography came soon after the
widespread development of computer
communications.
 In data and telecommunications, cryptography is
necessary when communicating over any
untrusted medium, which includes just about any
network, particularly the Internet.

8.  Authentication: The process of proving one's
identity. (The primary forms of host-to-host
authentication on the Internet today are name-
based or address-based, both of which are
notoriously weak.)
 Privacy/confidentiality: Ensuring that no one can
read the message except the intended receiver.
 Integrity: Assuring the receiver that the received
message has not been altered in any way from
the original.
 Non-repudiation: A mechanism to prove that the
sender really sent this message.

9.  We will discussed three type of Cryptographic
algorithms
1 Secret key cryptographic
2 Public key cryptographic
3 Hash function

11.  objective to recover key not just message
 general approaches:
◦ cryptanalytic attack
◦ brute-force attack
 if either succeed all key use compromised

12.  always possible to simply try every key
 most basic attack, proportional to key size
 assume either know / recognise plaintext
Key Size (bits) Number of Alternative
Keys
Time required at 1
decryption/µs
Time required at 106
decryptions/µs
32 232 = 4.3 109 231 µs = 35.8
minutes
2.15 milliseconds
56 256 = 7.2 1016 255 µs = 1142 years 10.01 hours
128 2128 = 3.4 1038 2127 µs = 5.4 1024
years
5.4 1018 years
168 2168 = 3.7 1050 2167 µs = 5.9 1036
years
5.9 1030 years
26 characters
(permutation)
26! = 4 1026 2 1026 µs = 6.4 1012
years
6.4 106 years