lecture 9 ,,,,.pptx - Encryption Introduction u2022 If you...

Encryption

Introduction
•
If you have the best firewall, very tight security policies, hardened
systems, virus scanners, intrusion-detection software, antispyware,
and every other computer security angle covered but send your data
in raw, plain text, then you simply are not secure.
•
There is the need to have messages changed in such a way that the
message cannot be easily read by an enemy, but they can be easily
decoded by the intended recipient
•
That's where cryptography / encryption is necessary

Cryptography Vs. Encryption
Cryptography
• The science of coding and decoding messages so as to keep these messages secure.
•
It is a discipline or techniques employed in protecting integrity or secrecy of electronic messages by
converting them into unreadable form. Only the use of a secret key can convert the cipher text back
into human readable form. Cryptography software and/or hardware devices use mathematical
formulas (algorithms) to change text from one form to another. The aim of cryptography is not to
hide the existence of a message, but rather to hide its meaning.
Encryption
•
Encryption is the process of encoding messages or information in such a way that only authorized
parties can read. Encryption protects against passive attack (eavesdropping).

Secure Communication Model
Alice
Bob
Oscar
Encrypt
Secret Key
x
y
Decrypt
K K
Secret Channel
K

Terminology
• Plaintext: This is the original message or data that is fed into the algorithm as input.
•
Encryption algorithm: The encryption algorithm performs various substitutions and
transformations on the plaintext.
•
Secret key: The secret key is also input to the algorithm. The exact substitutions and
transformations performed by the algorithm depend on the key.
• Ciphertext: This is the scrambled message produced as output. It depends on the
plaintext and the secret key. For a given message, two different keys will produce
two different ciphertexts.
•
Decryption algorithm: This is essentially the encryption algorithm run in reverse. It
takes the ciphertext and the same secret key and produces the original plaintext.
•
Cryptanalysis- The process of attempting to discover the plaintext or key is known as
cryptanalysis . The strategy used by the cryptanalyst depends on the nature of the
encryption scheme and the information available to the cryptanalyst

Types of Attacks on Encrypted
Messages

Types of Cryptography
•
There are two basic types of cryptography:
•
symmetric and asymmetric .
•
Symmetric means the same key is used to encrypt the message and to
decrypt the message.
•
With asymmetric cryptography, a different key is used to encrypt the
message than is used to decrypt the message

Symmetric key Encryption
•
Symmetric key encryption means that the same key is used to both encrypt and
decrypt a message. This is also referred to as Single-Key (Symmetric) Encryption.