Cryptography Intro
History
Since the time that people overcame literacy, they needed protection for the information they were writing and sending. It was necesery that only the sender and receiver knew how to understand the written information, and with that, a lot of people started to show interest in hiding written information, and the result was…a lot of great crypting methods. For that time.
Cryptography is about as old as the ancient pyramids.
Cryptography in Antiquity
The ancient Egyptians used a symbolic language. In 1998, a text written on stone slabs was deciphered. This text is over 6000 years old and is called the "Great Arcanum of Tarot." In it, the principles of the Universe are interpreted in a symbolic form, speaking of absolute and relative truth.
In ancient China, complex physical methods were invented to protect messages. Messages were hidden in secret compartments of the body.
European cryptography emerged in Greece. A significant impetus for its development was the fact that in Greece, for the first time, the European alphabet was finally formed (8th century BC). Until that moment, scripts that were poorly suited for cryptography had been widely used.
Two types of ciphers were used in ancient cryptography: substitution and transposition. A historical example of a substitution cipher is the Caesar cipher.
Cesar chiper
The letters were moved 3 letters in right for decryption. For encryption, move them to the left an you would get the full understandable message.
Scital
This was a method of sending hidden messages only if the reciever knew the exact R of the diametar needed. So when the script was rolled up on the cilindar a message could be seen.
Disk of Eney
It was a plate with letter writen all over the edges of it, and a hole above every letter. A knit would be put through the hole of the letters, and when pulled, following the knit would show the letters in order.
Polybius square
Polybius square is a simple method and it has only 25 spaces because in that time ‘i’ and ;j; were the same letter. Here is an example:
HELLO = 2315313134
Cryptography in Middle age
In the Middle Ages, cryptography persisted despite widespread illiteracy and the decline of scientific and artistic endeavors. Encryption methods included simple substitution ciphers, such as the Caesar cipher, and more complex systems using foreign alphabets. Notable figures in medieval cryptography include Saint Boniface, Roger Bacon, and Geoffrey Chaucer, who used encryption in their writings and diplomatic missions. Cryptographic practices were also observed in regions like Iraq, Tibet, Nigeria, and Thailand. Arab scholars made significant contributions to cryptography, developing methods for cryptanalysis and frequency analysis. Their works laid the foundation for modern cryptographic techniques. Encryption methods were closely guarded secrets, with cryptographers often facing destruction of their work to protect the secrecy of their ciphers.
Cryptography in Renesanse
During the Renaissance, cryptography advanced significantly with the work of scholars like Leon Alberti, Johannes Trithemius, and Giovanni Battista Bellaso. Alberti introduced a cipher based on a disk, considered fit for kings. Trithemius, a German scholar, proposed the "Ave Maria" cipher and a periodic shifting key cipher. Bellaso, an Italian, published "The Cipher of Signor Bellaso" in 1553, introducing a method for multialphabetic encryption using a memorable key or password. Another significant figure, Giovanni de la Porta, contributed to cryptography by combining ideas from Alberti, Trithemius, and Bellaso to create a mixed alphabet square and a method for bigram substitution. These developments laid the foundation for modern cryptography, including the use of complex tables for encryption and the concept of multialphabetic substitution.
Cryptography in new and modern world
During the Renaissance, cryptography was more of an art practiced by individuals, but its scientific foundations began to emerge with the development of serious methods for mathematical research. The six basic requirements for a cryptosystem were first outlined in the book "Military Cryptography" by Auguste Kerckhoffs (published in 1883). These requirements shaped the design of cryptographically secure systems:
Security: The system must be secure even if the attacker knows the system (except for the key).
Inconvenience: The compromise of the system should not inconvenience the correspondents.
Key Management: The key should be easily communicable and memorable without written notes, and correspondents should be able to change the key at will.
Applicability: The system should be applicable to telegraph communication.
Portability: The system should be portable, requiring only one person to operate it.
Usability: The system should be easy to use, without requiring a long list of rules or causing significant mental stress.
Dr. Auguste Kerckhoffs, a Dutch linguist and cryptographer, formulated these requirements. His work laid the foundation for modern cryptography by emphasizing the importance of key management, ease of use, and resilience against attacks.
Claude Shannon, an American mathematician and electronic engineer, made exceptional contributions to applying mathematical methods to cryptography. In 1944, Shannon completed the development of the theory of secret communications, and in 1945, he prepared the classified report "The Mathematical Theory of Cryptography," which was declassified and published in 1949. This report presented the theory of secret ciphers as mathematical models of ciphers.
Shannon's concepts of theoretical and practical secrecy allowed for the quantitative assessment of cryptographic qualities and the attempt to construct perfect or nearly perfect ciphers. His concept of redundancy in messages led to the idea that encryption should remove redundancy to make cryptanalysis more difficult.
Shannon also introduced the concept of the "operational characteristics" of a cipher, approaching a practical evaluation of its robustness. His work laid the foundation for modern cryptography, emphasizing the importance of strong keys, minimal redundancy in messages, and operational efficiency.
Basic cryptographic terms:
Cryptographic resilience: This concept characterizes the cipher itself, determining its resistance to decryption. It defines the duration required for decryption.
Cryptosystem: A set of reversible transformations that convert plaintext into ciphertext and vice versa.
Encryption: Some type of transformation that protects data from being revealed without the knowledge of a special key.
Key: Specific information that encrypts data.
Cipher: A set of reversible transformations that convert plaintext into ciphertext.
Decryption: The process of converting ciphertext into plaintext with a known key and algorithm.
Imitation protection: Protection against false data, adding an imitation-attachment to the encrypted data.
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