Cryptography is the practice and study of securing communication through techniques like encryption. It has evolved through manual, mechanical, and modern eras using computers. Cryptography aims to achieve goals like authentication, confidentiality, integrity, and non-repudiation. Common attacks include brute force, chosen plaintext, and differential power analysis. Symmetric cryptography uses a shared key while asymmetric uses public/private key pairs. Digital signatures and watermarks can authenticate documents. DRM and watermarks control digital content distribution.

1. TechKnowXpress
Cryptography

2. 
Cryptography (from Greek kryptós, "hidden",
+ gráphein, "to write").

Cryptography is the practice and study of
techniques for secure communication in the
presence of third parties (called adversaries).

It is about constructing and analyzing protocols
that overcome the influence of adversaries.
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3. 
There are three eras in the history of Cryptography:
 The Manual era
 The Mechanical era
 The Modern era

Manual era refers to Pen and Paper Cryptography and dates
back to 2000 B.C.eg : Scytale, Atbash , Caesar, Vigenere.

Mechanical era refers to the invention of cipher machines. E.g.:
Japanese Red and Purple Machines , German Enigma.

The modern era of cryptography refers to computers.

There are infinite permutations of cryptography available using
computers. E.g.: Lucifer, Rijndael , RSA , ElGamal.
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4. 
Cipher: the algorithm that does the encryption.

Ciphertext: the encrypted (scrambled) version of
the message. Message altered to be unreadable by
anyone except the intended recipients.

Cryptanalysis: the science of breaking
cryptographic algorithms.

Cryptanalyst: a person who breaks cryptographic
codes; also referred to as “the attacker”.
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5. 
Cryptosystem – The combination of
algorithm, key, and key management functions used
to perform cryptographic operations.

Decryption: the process of converting ciphertext
back to the original plaintext.

Encryption: scrambling a message or data using a
specialized cryptographic algorithm.

Initialization Vector – Random values used with
ciphers to ensure no patterns are created during
encryption.
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6. 
Key – Sequence that controls the
operation and behavior of the
cryptographic algorithm.

Keyspace – Total number of possible
values of keys in a crypto algorithm.

Plaintext – A message in its natural
format readable by an attacker.
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7. Authentication
 ensures that whoever supplies or
accesses sensitive data is an authorized
party.
Confidentiality
 assures that only authorized parties are
able to understand the data.
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8. Integrity
 ensures that when a message is sent over a
network, the message that arrives is the
same as the message that was originally
sent.
Nonrepudiation
 ensuring that the intended recipient actually
received the message & ensuring that the
sender actually sent the message.
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9. Brute force
 Trying all key values in the keyspace.
Chosen Ciphertext
 Decrypt known ciphertext to discover key.
Dictionary Attack
 Find plaintext based on common words.
Frequency Analysis
 Guess values based on frequency of
occurrence.
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10. Factoring Attacks
 Find keys through prime factorization.
Replay Attack
 Repeating previous known values.
Side channel attacks
 use seemingly incidental information
that can reveal important information
about the key being used.
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11. 


Chosen plaintext attacks
The cryptanalyst introduces the plaintext into
the system and then watches for how that
plaintext will be encrypted.
The Allies used this approach in WWII by
sending out false messages about allied troop
movements.
Often the attacker will try to feed a planned
sequence of messages that would reveal the
most about the way in which the data is being
encrypted.
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12. Known plaintext attack



The attacker has both the ciphertext and the
plaintext.
The attacker knows the algorithm that was
used for the encryption.
This is difficult because there are so many
keys, but the plaintext information may
make experimentation easier than in the
previous case.
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13. Differential Power Analysis
 This is an attack on smart cards.
 A DPA attack analyzes the power output
from a processor performing an
encryption algorithm in order to get
information about the key being used by
that algorithm.
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14. 
There are several size of
encryption keys:






64 bit encryption
128 bit encryption
256 bit encryption
512 bit encryption
1024 bit encryption
Number indicates the size of the
key used to encrypt the message.
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15. o
o
o
Symmetric
Even if an attacker captures the data, the attacker will not be
able to manipulate it in any meaningful way.
Symmetric algorithms use a single key shared by two
communicating parties.
The same key is used for both encryption and decryption.
Asymmetric
Mathematically related key pairs for encryption and
decryption.
o Public and private keys.
o
Hybrid
Combines strengths of both methods.
o TechKnowXpressdistributes symmetric key.
Asymmetric
o
Cryptography 15

16. Asymmetric Cryptography
Symmetric Cryptography
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17. Types of Symmetric Cryptography:
Stream-based Ciphers
 Mixes plaintext with key stream.
 Good for real-time services.
Block Ciphers
 Substitution and transposition.
 E.g.: DES, AES.
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18. Public Key Cryptography

In public-key cryptosystems, the
public key may be freely
distributed, while its paired private
key must remain secret and is used
for decryption.

Public-key cryptography can be used
for implementing digital
signature schemes.
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20. 
Quantum cryptography describes the use
of quantum mechanical effects (in
particular quantum communication
and quantum computation) to
perform cryptographic tasks or to break
cryptographic systems.
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21. 
The advantage of quantum cryptography is
that it allows the completion of various
cryptographic tasks that are proven or
conjectured to be impossible using only
classical communication.

For example, quantum mechanics
guarantees that measuring quantum data
disturbs that data. This can be used to
detect eavesdropping in quantum key
distribution.
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22. 
Digital signatures can be
permanently tied to the content of
the message being signed. They
cannot then be 'moved' from one
document to another, for any
attempt will be detectable.

RSA and DSA are two of the most
popular digital signature schemes.
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23. 
In digital signature schemes, there are two
algorithms: one for signing, in which a secret
key is used to process the message and one for
verification, in which the matching public key is
used with the message to check the validity of
the signature.
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24. 
Traditionally, a watermark has been
used to verify the authenticity of a
document.
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25. 
Driver’s Licenses, diplomas, official
letterhead were the primary
applications of watermarks . More
recently, used to track or prevent
redistribution of TV logos.
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26. 
Purpose of using:
 Ensure authenticity of digital goods.
 Prevent unauthorized use/ensures
copyright.
 Prevent copying.

Adding the watermark to the image
itself
prevents removal by
changing the format.
E.g. GIF->JPEG.
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27. 
DRM is the practice of imposing
technological restrictions that control
what users can do with digital media.

DRM is a class of controversial
technologies that are used by
hardware
manufacturers, publishers, copyright
holders, and individuals with the
intent to control the use of digital
content and devices after sale.
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