Cryptography is the practice of securing communications through techniques like encryption and decryption. It involves constructing algorithms to protect information from adversaries and ensure data confidentiality, integrity, and authentication. The main types are transposition ciphers, which rearrange letters, and substitution ciphers, which replace letters. Modern cryptography expanded with computers to encrypt any data and uses symmetric key cryptography, where senders and receivers share a key, and public key cryptography, where they have different keys. It has many applications including ATMs, email, remote access, and smart cards.

2. What is cryptography?
Cryptography is the practice and study of techniques
for secure communication in the presence of third parties
(called adversaries).
More generally, it is about constructing and analyzing that
overcome the influence of adversaries and which are
related to various aspects in information security such as
data confidentiality, data integrity, and authentication.

4. HISTORY OF CRYPTOGRAPHY
THE ORIGIN OF CRYPTOGRAPHY TOOK PLCAE AROUND
2000 B.C. IN EGYPT.
Before the modern era, cryptography was concerned solely with
message confidentiality (i.e., Encryption)—conversion of
messages from a comprehensible form into an incomprehensible
one and back again at the other end, rendering it unreadable by
interceptors or eavesdroppers without secret knowledge.
Encryption was used to ensure secrecy in communications,
such as those of spies, military leaders, and diplomats.

5. CLASSIC CRYPTOGRAPHY
The main classical cipher types are transposition
ciphers, which rearrange the order of letters in a message and
substitution ciphers, which symmetrically replace letters with
other letters.
EXAMPLE., ‘hello world’ becomes 'ehlol owrdl' in a trivially
simple rearrangement scheme.
A cipher (or cypher) is an algorithm for performing
encryption or decryption — a series of well-defined
steps that can be followed as a procedure.

6. An early substitution cipher was the Caesar cipher, in which each letter in
the plain text was replaced by a letter some fixed number of positions further
down the alphabet.
Suetonius reports that Julius Caesar used it with a shift of three to
communicate with his generals.
Reconstructed ancient Greek scytale
(rhymes with "Italy"), an early cipher device.

9. THE COMPUTER
ERA
OR
MODERN
CRYPTOGRAPHY

10. • 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.
German Lorenz cipher machine, used in World
War II to encrypt very-high-level general
staff messages.

11. •These days a fine example of cryptography is
Credit card with smart-card capabilities. The 3-by-5-mm chip
embedded in the card is shown, enlarged. Smart cards combine low cost
and portability with the power to compute cryptographic algorithms

12. Padlock icon from the Firefox Web
browser, meant to indicate a page has been sent
in SSL or TLS-encrypted protected form.
However, seeing an icon results when code is
intended to render it. Malicious code can provide
the icon even when the connection is not actually
being protected by SSL or TLS

13. This is a
CRYPTOGRAPHY
PIECE

14. The mod e r n f ie ld o f c rypt ogra phy c a n be
d ivid e d in t o s e ve r a l a r e a s o f s t u d y :
SYMMETRIC KEY CRYPTOGRAPHY :
Symmetric-key cryptography refers to encryption methods in
which both the sender and receiver share the same key
PUBLIC KEY CRYTOGRAPHY :
Public key cryptography refers to encryption methods in which
both the sender and receiver share the different keys.
The basic elements of cryptography are:
1. Encryption
2. Decryption
3. Key

16. The above example was of symmetric key cryptography.
Here we can see the difference between PUBLIC and
PRIVATE key

17. •The Data Encryption Standard (DES) and the Advanced
Encryption Standard (AES) are block cipher designs which have
been designated cryptography standards by the US government
(though DES's designation was finally withdrawn after the AES was
adopted).

18. PUBLIC KEY ENCRYPTION(Asymmetric key)

19. APPLICATIONS OF
CRYPTOGRAPHY
• ATM
• e-mail
• Secure remote access
• ISDN
• PEM
• PGD
• Smart Cards and many more