What is Cryptography...?
Encryption & Decryption
Types of Cryptography
What is KEY…?
Cryptography is the science of information security.
Derived from the Greek word “KRYPTOS”.
Writing in secret code and is an ancient art.
In data and telecommunications, cryptography is necessary
when communicating over any untrusted medium,
particularly the Internet.
Some specific security requirements
Authentication: The process of proving one's identity.
Privacy: 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.
It is the transformation of data into some unreadable form.
Its purpose is to keep the information hidden from anyone for whom it
is not intended.
It is the reverse of encryption.
It is transformation of encrypted data back into some clear
Types of Cryptography
Secret Key Cryptography: Uses a single key for both
encryption and decryption.
Public Key Cryptography: Uses one key for encryption and
another for decryption.
Hash Functions: Uses a mathematical transformation to
What is Key….?
In cryptographic systems, the term key refers to a numerical
value used by an algorithm to alter information, making that
information secure and visible only to individuals who have
the corresponding key to recover the information.
The art of protecting information by transforming it
into an unreadable format, called cipher text.
Secret Key Cryptography
It is also known as symmetric key cryptography.
Messages are encrypted by the sender using the key and
decrypted by the receiver using the same key.
Suitable for communicating with only a limited number of
Eg: DES , IDEA
Public Key Cryptography
Uses a pair of keys for encryption and decryption.
With public key cryptography, keys work in pairs of matched public
and private keys.
The public key can be freely distributed without compromising the
private key, which must be kept secret by its owner.
Because these keys work only as a pair, encryption initiated with the
public key can be decrypted only with the corresponding private key.
RSA(Ronald Rivest, Adi Shamir, and Leonard Adleman)
Public Key Private Key
Also called message digests and one-way encryption, are algorithms
that use no key.
A fixed-length hash value is computed based upon the plaintext that
makes it impossible for either the contents or length of the plaintext to
Typically used to provide a digital fingerprint of a file's contents.
Provide a measure of the integrity of a file.
Different Hash Algorithms
Message Digest (MD) algorithms: Produce a 128-bit hash value.
Secure Hash Algorithm (SHA): Produces a 160-bit hash value.
RIPEMD: RACE Integrity Primitives Evaluation. 32-bit
HAVAL: Hash of Variable Length hash values that are 128, 160,
192, 224, or 256 bits in length.
Whirlpool: Operates on messages less than 2256 bits in length,
and produces a message digest of 512 bits.
Tiger: Designed to be secure, run efficiently on 64-bit processors.
Sent thru’ Internet
It hides the message and your privacy is safe.
No one would be able to know what it says unless there's a key to
You can write what ever you want and how ever you want (any
theme any symbol for the code) to keep your code a secret.
You are able to use Cryptography during lessons without the teacher
Takes a long time to figure out the code.
It takes long to create the code.
If you were to send a code to another person in the past, it will take
long to get to that person.
Overall it’s a long process.
As the Internet and other forms of electronic communication
become more prevalent, electronic security is becoming
Cryptography is used to protect e-mail messages, credit card
information, and corporate data.
One of the most popular cryptography systems used on the
Internet is Pretty Good Privacy because it's effective and