Cryptography is the practice of securing communications and data through encryption techniques. It aims to achieve authentication, privacy, integrity, and non-repudiation. The development of computers allowed for more complex encryption of digital data. There are different types of cryptography including secret key cryptography which uses a single key, and public key cryptography which uses different keys for encryption and decryption. Cryptography provides a secure way to transmit data and is necessary for communications over untrusted networks like the Internet.

2. INTRODUCTION
 the practice and study of techniques for constructing
and analyzing protocols that overcome the influence
of adversaries and which are related to various aspects
in information such as data confidentiality data
integrity and authentication
 Applications of cryptography include ATM cards,
computer passwords, and electronic commerce

3. REQUIREMENTS OF A
SECURE NETWORKS
 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

4. WORKING OF CRYPTOGRAPHY

5. OLDEST CRYPTOGRAPHY MACHINE

6. COMPUTER ERA
 The development of digital computers and electronics
after WWII made possible much more complex
ciphers. Furthermore, computers allowed for the
encryption of any kind of data
 Represent able in any binary format, unlike classical
ciphers which only encrypted written language texts;
this was new and significant. Computer use has thus
supplanted linguistic cryptography, both for cipher
design and cryptanalysis.

7. TYPES OF CRYPTOGRAPHY

8. SECRET KEY CRYPTOGRAPHY
 Uses a single key for both encryption and decryption
 With this type of cryptography, both the sender and
the receiver know the same secret code, called the key
 This method works well if you are communicating
with only a limited number of people, but it becomes
impractical to exchange secret keys with large
numbers of people. In addition, there is also the
problem of how you communicate the secret key
securely.

9. PUBLIC KEY CRYPTOGRAPHY
 Uses one key for encryption and another for
decryption.
 uses a pair of keys for encryption and decryption
 The public key can be freely distributed without
compromising the private key, which must be kept
secret by its owner.

10. HASH FUNCTION CRYPTOGRAPHY
 A hash function is any algorithm or subroutine that
maps large data cells, called keys, to smaller data sets.
For example, a single integer can serve as an index to
an array.
 Hash functions are mostly used to accelerate table
lookup or data comparison tasks such as finding items
in database, detecting duplicated or similar records in
a large file, finding similar stretches in DNA
sequences, and so on.

11. PURPOSE OF CRYPTOGRAPHY
 Cryptography is the science of writing in secret code
and is an ancient art; the first documented use of
cryptography in writing dates back to circa 1900 B.C.
 It provides more efficient way of security by encrypting
our data.
 It allows the sender and receiver to communicate more
securily
 It is used in armies from older ages to modern ages. It
allows the armies for exchanging information in the
efficient and secured way.

12. CONCLUSION
 Some experts argue that cryptography appeared
spontaneously sometime after writing was invented,
with applications ranging from diplomatic missives to
war-time battle plans. It is no surprise, then, that 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.