3. What is Cryptography?
Cryptography derived its name from
a Greek word called “Kryptos” which
means “Hidden Secrets”.
Cryptography is the practice and
study of hiding information.
It is the Art or Science of converting a
plain intelligible data into an
unintelligible data and again
retransforming that message into its
original form.
It provides
Confidentiality, Integrity, Accuracy.
4. What is Cryptography
Cryptography
In a narrow sense
Mangling information into apparent unintelligibility
Allowing a secret method of un-mangling
In a broader sense
Mathematical techniques related to information security
About secure communication in the presence of adversaries
Cryptanalysis
The study of methods for obtaining the meaning of encrypted
information without accessing the secret information
Cryptology
Cryptography + cryptanalysis
5. Cryptography is the science of secret writing is an
ancient art; the first documented use of cryptography in writing
dates back to circa 1900 B.C. when an Egyptian scribe used non-
standard hieroglyphs in an inscription.
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.
6. FUNCTIONS OF CRYTPGRAPHY
There are five primary functions of cryptography today:
1. Privacy/confidentiality: Ensuring that no one can read the
message except the intended receiver.
2. Authentication: The process of proving one's identity.
3. Integrity: Assuring the receiver that the received message has
not been altered in any way from the original.
4. Non-repudiation: A mechanism to prove that the sender really
sent this message.
5. Key exchange: The method by which crypto keys are shared
between sender and receiver.
7. In cryptography, we start with the unencrypted data, referred to
as plaintext. Plaintext is encrypted into ciphertext, which will in
turn (usually) be decrypted back into usable plaintext.
The encryption and decryption is based upon the type of
cryptography scheme being employed and some form of key. For
those who like formulas, this process is sometimes written as:
C=Ek(P)
P = Dk(C)
where P = plaintext, C = ciphertext, E = the encryption
method, D = the decryption method, and k = the key
8. What is Encryption / Decryption
Encryption –
◦ The process of converting plain text into an
unintelligible format (cipher text) is called
Encryption.
Decryption –
◦ The process of converting cipher text into a plain
text is called Decryption.
9. What is a Key
◦ In cryptography, a key is a variable value that is applied
using an algorithm to a string or block of unencrypted text
to produce encrypted text, or to decrypt encrypted text.
The length of the key is a factor in considering how
difficult it will be to decrypt the text in a given message.
What is a Block Cipher?
◦ A block cipher is an encryption method that applies a
deterministic algorithm along with a symmetric key to encrypt
a block of text, rather than encrypting one bit at a time as in
stream ciphers.
10. TYPES OF CRYPTOGRAPHIC ALGORITHMS
There are several ways of classifying cryptographic algorithms
The three types of algorithms that will be discussed are :
Secret Key Cryptography (SKC): Uses a single key for both
encryption and decryption; also called symmetric encryption.
Primarily used for privacy and confidentiality.
Public Key Cryptography (PKC): Uses one key for encryption
and another for decryption; also called asymmetric encryption.
Primarily used for authentication, non-repudiation, and key
exchange.
Hash Functions: Uses a mathematical transformation to
irreversibly "encrypt" information, providing a digital fingerprint.
Primarily used for message integrity.
12. What are the Types of Cryptography
Symmetric Key Cryptography (Secret Key Cryptography)
◦ Same Key is used by both parties
Advantages
1. Simpler and Faster
Disadvantages
1. Less Secured
13. Asymmetric Key Cryptography (Public Key Cryptography)
◦ 2 different keys are used
◦ Users get the Key from an Certificate Authority
Advantages
1. More Secured
2. Authentication
Disadvantages
1. Relatively Complex
14. Secret Key Cryptography
Using a single key for encryption/decryption.
The plaintext and the ciphertext having the same size.
Also called symmetric key cryptography
plaintext
ciphertext plaintext
ciphertext
decryption
encryption
key
15. Secret Key Cryptography
Using a single key for encryption/decryption.
The plaintext and the ciphertext having the same size.
Also called symmetric key cryptography
plaintext
ciphertext plaintext
ciphertext
decryption
encryption
key
