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Cryptography or Cryptology is the practice and study of techniques for secure communication in the presence of adversarial behavior. 

In general, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. It covers various aspects in information security such as;

• Data Confidentiality
• Data Integrity
• Authentication 
• Non-Repudiation (where a statement's validity cannot be disputed)

Modern cryptography exists at the intersection of the disciplines of;

• Mathematics
• Computer Science
• Electrical Engineering
• Communication Science
• Physics

Applications of Cryptography;

• Electronic Commerce
• Chip Based Payment Cards
• Digital Currencies
• Computer Passwords
• Military Communications

Cryptography prior to the modern age was effectively synonymous with encryption, converting information from a readable state to unintelligible nonsense.

The sender of an encrypted message shares the decoding technique only with intended recipients to preclude access from adversaries. Since the development of cryptographer machines since World War I, cryptography has become more sophisticated. 

Modern cryptography is heavily based on mathematical theory and computer science practice and is made complex so that these are hard to break in actual practice by adversaries.

Issues with Modern Cryptography
The growth of cryptographic technology has raised a number of legal issues in the Information Age. Cryptography's potential or use as a tool for espionage and sedition has led many governments to classify it as a weapon and to limit or even prohibit its use and export. 

In some jurisdictions where the use of cryptography is legal, laws permit investigators to compel the disclosure of encryption keys for documents relevant to an investigation. Cryptography also plays a major role in digital rights management and copyright infringement disputes in regard to digital media.

Examples of Modern Cryptography

1. Symmetric Key Cryptography
2. Public Key Cryptography