Cryptography .pptx

cryptography seminar ppt

1. Cryptography

2. introduction Cryptography is the art and science of securing communication and data from unauthorized access and alterations. It involves mathematical techniques and algorithms that transform information into a secure format, making it unreadable to anyone who does not possess the appropriate key. Plaintext : The original, readable information that is to be protected. Ciphertext : The scrambled, unreadable output produced after encryption Encryption : The process of converting plaintext into ciphertext using an algorithm and a key. Decryption : The reverse process that transforms ciphertext back to plaintext.

3. Symmetric Cryptography Symmetric cryptography, also known as secret-key cryptography, is a type of encryption where the same key is used for both encrypting and decrypting information. This method relies on the confidentiality of the key, which must be kept secret from unauthorized users. The primary advantage of symmetric cryptography is its efficiency, as it typically requires less computational power compared to asymmetric cryptography .

4. How Symmetric Cryptography Works Key Generation : A secret key is generated, which is used for both encryption and decryption. Encryption : The plaintext (original message) is transformed into ciphertext (encrypted message) using the secret key and a specific encryption algorithm. Transmission : The ciphertext is transmitted to the intended recipient. Decryption : The recipient uses the same secret key and the corresponding decryption algorithm to convert the ciphertext back into plaintext.

5. Traditional cipher Traditional ciphers refer to classical encryption techniques that were used before the advent of modern cryptography. These methods are primarily manual and rely on simple algorithms to encrypt and decrypt messages. Substitution Cipher Traditional ciphers refer to classical encryption techniques that were used before the advent of modern cryptography. These methods are primarily manual and rely on simple algorithms to encrypt and decrypt messages.

6. Caesar Cipher: The  Caesar cipher  is one of the simplest and most well-known encryption techniques. It is a type of substitution cipher where each letter in the plaintext is shifted a fixed number of places down or up the alphabet. How It Works Shift Value : The number of positions each letter is shifted is known as the "shift" or "key." For example, a shift of 3 means that 'A' becomes 'D', 'B' becomes 'E', and so on. Alphabet Wrap-Around : The alphabet wraps around at the end. So, if the shift goes beyond 'Z', it starts again at 'A'. For example, with a shift of 3: X → A Y → B Z → C

7. Example Shift of 3 : Plaintext : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Ciphertext : D E F G H I J K L M N O P Q R S T U V W X Y Z A B C Encryption Process : To encrypt the message "HELLO": H → K (H + 3) E → H (E + 3) L → O (L + 3) L → O (L + 3) O → R (O + 3) Result : The ciphertext is "KHOOR".

8. Decryption To decrypt a message encrypted with the Caesar cipher, you simply shift in the opposite direction by the same number. For example, for a shift of 3: K → H (K - 3) H → E (H - 3) O → L (O - 3) O → L (O - 3) R → O (R - 3) Result : The decrypted message is "HELLO".

9. Vigenère Cipher: is a method of encrypting alphabetic text by using a simple form of polyalphabetic substitution. It employs a keyword to determine the shift for each letter in the plaintext, making it more secure than simple substitution ciphers like the Caesar cipher. Key Features Keyword-Based Encryption : The cipher employs a keyword that determines the shift for each letter in the plaintext. Each letter of the keyword corresponds to a specific numerical value based on its position in the alphabet (A=0, B=1, ..., Z=25). Polyalphabetic Substitution : Unlike simple substitution ciphers, where each letter is consistently replaced by another, the Vigenère cipher allows for multiple substitutions for each plaintext letter based on the keyword. This enhances security by making frequency analysis more challenging.

10. Encryption Process The plaintext is aligned with the repeated keyword. Each letter in the plaintext is shifted according to the corresponding letter in the keyword. The shifts are calculated using modular arithmetic to ensure wrap-around within the alphabet. Decryption Process To decrypt, the same keyword is used, but the shifts are reversed. The ciphertext is aligned with the keyword, and each letter is shifted back according to the corresponding letter of the keyword.

11.   transpositional cipher A  transpositional cipher  is a type of encryption method where the positions of the characters in the plaintext are shifted according to a regular system. Unlike substitution ciphers, where the characters themselves are altered, transpositional ciphers rearrange the order of the characters. Plaintext : The original message you want to encrypt. Rearrangement : The characters are rearranged based on a specific rule, often involving a key. The working of a  transpositional cipher  involves rearranging the characters of the plaintext according to specific rules, rather than altering the characters themselves.

12. Block Cipher A  block cipher  is a type of symmetric key cipher that encrypts data in fixed-size blocks. Instead of encrypting one bit or one byte at a time, block ciphers take a block of plaintext and transform it into a block of ciphertext using a secret key. Key Characteristics of Block Ciphers Block Size : Common block sizes include 64 bits (e.g., DES) and 128 bits (e.g., AES). The choice of block size can affect both security and performance. Key Size : The length of the encryption key can vary, commonly ranging from 128 bits to 256 bits. Longer keys generally provide better security. Symmetric Encryption : The same key is used for both encryption and decryption, necessitating secure key management.

13. How Block Ciphers Work Block ciphers typically operate through the following steps: Plaintext Input : The data is divided into fixed-size blocks. If the plaintext does not perfectly fit into the block size, padding is added. Key Scheduling : The original key is expanded into a series of round keys, which will be used in the encryption process. Rounds of Transformation : The encryption process consists of multiple rounds (often 10, 12, or 14) of transformation, which includes: Substitution : Replacing bits or groups of bits with other bits based on a substitution box (S-box). Permutation : Rearranging bits to diffuse the plaintext throughout the ciphertext. Mixing : Combining the bits of the data block using mathematical operations. Output : After processing all rounds, the final output is the ciphertext block.

14. Data Encryption Standard (DES) The  Data Encryption Standard (DES)  is a symmetric-key block cipher that was widely used for data encryption. It was adopted as a federal standard in the United States in 1977 and became one of the most popular encryptionn methods in the late 20th century.

15. The Data Encryption Standard (DES) is a symmetric-key block cipher that encrypts data in 64-bit blocks using a 56-bit key. The encryption process begins with an initial permutation of the plaintext block, which is then divided into two halves. Over 16 rounds of transformation, the right half undergoes expansion and is XORed with a round key derived from the original key. This result is processed through S-boxes for substitution and permuted to enhance diffusion. After each round, the left and right halves are swapped, and this process continues until all rounds are completed. Finally, a final permutation is applied to produce the ciphertext, ensuring that the original data is securely obscured.

16. Electronic Codebook (ECB) :  Electronic Codebook (ECB) :  Electronic Codebook (ECB) mode is a straightforward encryption method where plaintext is divided into fixed-size blocks, and each block is encrypted independently using the same key. This means that identical plaintext blocks produce identical ciphertext blocks, making ECB easy to implement and allowing for parallel processing. However, this independence can lead to security vulnerabilities, as patterns in the plaintext can be exposed in the ciphertext. Because of these weaknesses, ECB is generally not recommended for encrypting sensitive information.

17. Cipher Block Chaining (CBC) Cipher Block Chaining (CBC) mode is an encryption method that enhances security by linking the encryption process of each block to the previous block. In CBC, the plaintext is divided into fixed-size blocks, and before encrypting each block, it is XORed with the ciphertext of the previous block. For the first block, an initialization vector (IV) is used to ensure that identical plaintext blocks produce different ciphertexts. This chaining process means that even if the same plaintext is encrypted multiple times, the resulting ciphertext will be different each time, significantly improving security against pattern analysis

18. Public Key Cryptography Public key cryptography , also known as asymmetric cryptography, is a cryptographic system that uses a pair of keys—one public and one private—for secure communication. Key Characteristics Key Pair : Each user has two keys: Public Key : This key is shared openly and can be distributed to anyone. Private Key : This key is kept secret and is known only to the owner. Asymmetric : Unlike symmetric cryptography, where the same key is used for both encryption and decryption, public key cryptography employs different keys for these operations.

19. How It Works Encryption : When someone wants to send a secure message, they encrypt the plaintext using the recipient's public key. This ensures that only the recipient can decrypt it with their corresponding private key. Decryption : The recipient uses their private key to decrypt the received ciphertext, restoring the original plaintext. Digital Signatures : Public key cryptography also enables digital signatures, where a sender can sign a message with their private key. Recipients can verify the signature using the sender's public key, ensuring authenticity and integrity.