Unit -1 cryptography contiues with algorithm.pptx

Symmetric Key Cryptography
8. Introduction to Modern Symmetric Key Ciphers- DES, Blowfish, IDEA, AES, RC5,
9. Modes of operation of Modern Symmetric Key Ciphers
10. Asymmetric Key Cryptography – RSA
11. Digital signatures and Digital Certificates
12. Certificate Authority and key management Kerberos
13. X.509 Directory Authentication Service

1. Cryptography is the practice and study of techniques for securing communication and data in the presence of adversaries. cryptography

2. Encryption Algorithms Cryptography is broadly classified into two categories:  Symmetric key Cryptography  and  Asymmetric key Cryptography  (popularly known as public key cryptography).

3. Symmetric Key Cryptography An encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message. The most popular symmetric–key system is the Data Encryption Standard (DES)

4. 2. Hash Functions: There is no usage of any key in this algorithm. A hash value with a fixed length is calculated as per the plain text which makes it impossible for the contents of plain text to be recovered. Many operating systems use hash functions to encrypt passwords. Transposition Ciphers: In Cryptography, a transposition cipher is a method of encryption by which the positions held by units of plaintext (which are commonly characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext.  Types of Transposition Cipher Techniques There are three types of transposition cipher techniques Rail Fence Transposition Cipher Block (Single Columnar) Transposition Cipher Double Columnar Transposition Cipher

5. Rail Fence Transposition Cipher Rail Fence Transposition cipher technique is the simplest transposition cipher technique its . It is also termed as a zigzag cipher. It gets its name from the way through which it performs encryption of plain text. The steps to get cipher text with the help of the   Rail Fence Transposition cipher  technique are as follow- Cipher Text : hlorsnelkiha

6. Block (Single Columnar) Transposition Cipher Block Transposition Cipher is another form of Transposition Cipher which was used to encrypt the message or information. In this technique, first, we write the message or plaintext in rows. After that, we read the message column by column. In this technique, we use a keyword to determine the no of rows. Step 1: First we write the message in the form of rows and columns, and read the message column by column. Step 2: Given a keyword, which we will use to fix the number of rows. Step 3: If any space is spared, it is filled with null or left blank or in by (_). Step 4: The message is read in the order as specified by the keyword. For example: The plaintext is "KRISHNA RANJAN" Now we will write the plaintext in the form of row and column. Cipher Text = IAN_RNANS_J_KHRA

7. Double Columnar Transposition Cipher Double Columnar Transposition Cipher is another form of Transposition Cipher Technique. It is just similar to the columnar transposition technique. The main objective of using a Double  Columnar Transposition Cipher  is to encrypt the message twice. It makes use of the Single Columnar Transposition technique but uses two times. It can use the same or different secret keys. The output obtained from the first encryption will be the input to the second encryption. Step 1: First we write the message in the form of rows and columns, and read the message column by column. Step 2: Given a keyword, which we will use to fix the number of rows. Step 3: If any space is spared, it is filled with null or left blank or in by (_). Step 4: The message is read in the order in by the keyword. Step 5: Then the output from the first  encryption  is input to the second. Step 6: Now the message is read in Technique in the order specified by the second keyword.

8. Introduction to Modern Symmetric Key Ciphers- DES, Blowfish, IDEA, AES, RC5, Modern cryptosystems need to process this binary strings to convert in to another binary string. 1. Block Ciphers: In this, the plain binary text is processed in blocks (groups) of bits at a time; i.e. a block of plaintext bits is selected, a series of operations is performed on this block to generate a block of ciphertext bits. The number of bits in a block is fixed. For example, the schemes DES and AES have block sizes of 64 and 128. 2. Stream Ciphers: In this scheme, the plaintext is processed one bit at a time i.e. one bit of plaintext is taken, and a series of operations is performed on it to generate one bit of ciphertext. Technically, stream ciphers are block ciphers with a block size of one bit.

9. Feistel Cipher Feistel Cipher model is a structure or a design used to develop many block ciphers such as DES. Feistel cipher may have invertible, non-invertible and self invertible components in its design. Same encryption as well as decryption algorithm is used. A separate key is used for each round. However same round keys are used for encryption as well as decryption.    Feistel cipher algorithm Create a list of all the Plain Text characters.  Convert the Plain Text to Ascii and then 8-bit binary format.  Divide the binary Plain Text string into two halves: left half (L1)and right half (R1)  Generate a random binary keys (K1 and K2) of length equal to the half the length of the Plain Text for the two rounds. 

10. DES(Data Encryption Standard) : Data Encryption Standard (DES) is a block cipher with a 56-bit key length that has played a significant role in data security .  Data encryption standard (DES) has been found vulnerable to very powerful attacks therefore, the popularity of DES has been found slightly on the decline. DES is a block cipher and encrypts data in blocks of size of  64 bits  each, which means 64 bits of plain text go as the input to DES, which produces 64 bits of ciphertext. The same algorithm and key are used for encryption and  decryption , with minor differences. The key length is  56 bits . 

11. In the first step, the 64-bit plain text block is handed over to an initial  Permutation  (IP) function. The initial permutation is performed on plain text. Next, the initial permutation (IP) produces two halves of the permuted block; saying Left Plain Text (LPT) and Right Plain Text (RPT). Now each LPT and RPT go through 16 rounds of the encryption process. In the end, LPT and RPT are rejoined and a Final Permutation (FP) is performed on the combined block The result of this process produces 64-bit ciphertext.

12. Blowfish

13. Modes of operation of Modern Symmetric Key Ciphers Symmetrical Key Cryptography also known as conventional or single-key encryption was the primary method of encryption before the introduction of public key cryptography in the 1970s. In symmetric-key algorithms, the same keys are used for data encryption and decryption. This type of cryptography plays a crucial role in securing data because the same key is used for both encryption and decryption.

14. Techniques Used in Symmetric Key Cryptography Substitution  and  Transposition  are two principal techniques used in symmetric-key cryptography. Substitution Techniques The symmetric key cryptographic method employs one secret key for the operations of encryption and decryption. Substitution techniques provide two significant approaches, wherein elements (letters, characters) from the plaintext message are replaced with new elements according to the rules based on the secret key. Caesar Cipher:  Caesar cipher  has   since their predictability is so complete and no complexity is invested. Monoalphabetic Ciphers:  This is where the ciphers use one rule of substitution throughout the message. This may involve replacing letters with numbers, symbols, or another set of letters in another order. Playfair Cipher:  Implementation of repeated letters or letter pairs can expose patterns, and cryptanalysis techniques exist to exploit them. Hill Cipher:  This cipher operates on blocks of letters (typically bigrams or trigrams) using a matrix multiplication approach. The  Hill ciphers  have a limitation on key size and susceptibility towards cryptanalysis for larger key sizes. Polyalphabetic Ciphers:  This is the type of cipher where any one of the letters in the plaintext is substituted by a different letter to keep frequency analysis challenging. For example, the  Vigenère cipher  operates with a keyword that would determine the shift value for each letter in the plaintext. One-Time Pad (OTP):  It is a theoretically impossible cipher where the key is a random string of characters that is exactly as long as the message itself. The key is used for a single encryption and then discarded.

15. Types of Symmetric Key Cryptography Stream Ciphers Block Ciphers Applications of Symmetric Key Cryptography Data encrypting/decrypting:  SKC widely applies to protect sensitive data either statically stored in some device or transmitted through the network. Some of these applications include the authentication of users' credentials, encryption of email messages, and financial transactions. Secure communication:  The majority of the communication protocols commonly used are  SSL/TLS , which use the combination of symmetric and asymmetric key encryption to ensure the confidentiality and integrity of exchanged information between two parties. These messages will be encrypted and decrypted using symmetric key encryption using a shared key. Authenticity verification:  In some places, SKC is applied using techniques like  message authentication codes  (MACs) and keyed-hash MACs (HMACs) to authenticate the messages by verifying their authenticity and integrity, thus ensuring tamper-resistant communication. File and disk encryption:  Full-disk encryption software and file encryption tools also apply SKC to encrypt sensitive data stored in hard disks or portable storage devices. Virtual private networks:  VPN  technologies are technologies that aim to provide confidential communication channels free from eavesdropping. Some of these may use symmetric or asymmetric key encryption to connect remote users and corporate networks.

16. Principles of Symmetric Key Encryption Basic principles which underpin the security of symmetric key encryption algorithms. Resistance to brute force attack:  The most basic requirement for the security of an encryption cipher is that the keyspace size—in other words, the number of possible distinct keys from which someone using the algorithm could have chosen—is very large. Cryptographic attack resistance:  The second fundamental requirement for symmetric or non-symmetrical encryption is the ability to generate information-influenced (i.e., non-random) encrypted messages. For this to happen, a critical but not sufficient requirement in an informational sense is that the encrypted message has high entropy. It would, in other words, be impossible for an attacker to infer any information about the plain text or secret key from having tried to analyze the ciphertext by the use of frequency analysis or other statistical techniques. Resistance to general forms of cryptanalytic attacks sufficient to ensure semantic security is formalized via the notion of indistinguishability. Advantages of Symmetric Key Cryptography Speed and efficiency : Symmetric key+ algorithms are better suited for encrypting large volumes of data or for use in real-time communication scenarios as they are faster and less resource-intensive than asymmetric cryptography. SKC algorithms do not involve algebraically mathematical operations. Scalability : Because symmetric key algorithms have relatively low computational overhead, they scale well with the number of users and the amount of data being encrypted. Simplicity : Symmetric encryption protocols are often more straightforward to implement and understand than  asymmetric key methods , and this would go a long way in attracting developers and users.

17. Asymmetric Key Cryptography – RSA . RSA Algorithm (Rivest, Shamir, Adleman Algorithm) RSA is an basic asymmetric cryptographic algorithm which uses two different keys for encryption. The RSA algorithm works on a block cipher concept that converts plain text into cipher text and vice versa. RSA algorithm is an asymmetric cryptography algorithm. Asymmetric actually means that it works on two different keys i.e.  Public Key and Private Key . As the name describes that the Public Key is given to everyone and the Private key is kept private. Characteristics of RSA Algorithm Security:  Many consider the RSA method to be highly secure and widely used for transmitting data Fast Speed : The RSA approach is known for its speed. Can be implemented swiftly when cryptography needs arise. Different keys:  In the RSA technique two separate keys are utilized for encrypting and decrypting data. The public key is used to encrypt the information while the private key is employed for decryption. Key exchange:  With the RSA method secure exchange can be achieved, enabling two parties to swap a key without transmitting it over the network.

18. Key Generation:

19. Digital signatures and Digital Certificates Digital signatures  and  certificates  are two key technologies that play a crucial role in ensuring the security and authenticity of online activities. They are essential for activities such as online banking, secure email communication, software distribution, and electronic document signing. By providing mechanisms for authentication, integrity, and non-repudiation, these technologies help protect against fraud, data breaches, and unauthorized access. Digital Signature A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software, or digital document. These are some of the key features of it. Key Generation Algorithms: Digital signatures are electronic signatures, which assure that the message was sent by a particular sender. While performing digital transactions authenticity and integrity should be assured, otherwise, the data can be altered or someone can also act as if he were the sender and expect a reply. Signing Algorithms: To create a digital signature, signing algorithms like email programs create a one-way hash of the electronic data which is to be signed. The signing algorithm then encrypts the hash value using the private key (signature key). This encrypted hash along with other information like the hashing algorithm is the digital signature. This digital signature is appended with the data and sent to the verifier. The reason for encrypting the hash instead of the entire message or document is that a hash function converts any arbitrary input into a much shorter fixed-length value. This saves time as now instead of signing a long message a shorter hash value has to be signed and hashing is much faster than signing. Signature Verification Algorithms: The Verifier receives a Digital Signature along with the data. It then uses a Verification algorithm to process the digital signature and the public key (verification key) and generates some value. It also applies the same hash function on the received data and generates a hash value. If they both are equal, then the digital signature is valid else it is invalid.

20. Assurances About Digital Signatures The definitions and words that follow illustrate the kind of assurances that digital signatures offer. Authenticity : The identity of the signer is verified. Integration:  Since the content was digitally signed, it hasn’t been altered or interfered with. Non-repudiation:  demonstrates the source of the signed content to all parties. The act of a signer denying any affiliation with the signed material is known as repudiation. Notarization:  Under some conditions, a signature in a Microsoft Word, Microsoft Excel, or Microsoft PowerPoint document that has been time-stamped by a secure time-stamp server is equivalent to a notarization. Benefits of Digital Signatures Legal documents and contracts:  Digital signatures are legally binding. This makes them ideal for any legal document that requires a signature authenticated by one or more parties and guarantees that the record has not been altered. Sales contracts:  Digital signing of contracts and sales contracts authenticates the identity of the seller and the buyer, and both parties can be sure that the signatures are legally binding and that the terms of the agreement have not been changed. Financial Documents:  Finance departments digitally sign invoices so customers can trust that the payment request is from the right seller, not from a attacker trying to trick the buyer into sending payments to a fraudulent account. Health Data:  In the healthcare industry, privacy is paramount for both patient records and research data. Digital signatures ensure that this confidential information was not modified when it was transmitted between the consenting parties.

21. Digital Certificate Digital certificate is issued by a trusted third party which proves sender’s identity to the receiver and receiver’s identity to the sender. A digital certificate is a certificate issued by a Certificate Authority (CA) to verify the identity of the certificate holder. Digital certificate is used to attach public key with a particular individual or an entity.  Digital Certificate Contains Name of certificate holder. Serial number which is used to uniquely identify a certificate, the individual or the entity identified by the certificate Expiration dates. Copy of certificate holder’s public key. (used for decrypting messages and digital signatures) Digital Signature of the certificate issuing authority.

22. Advantages of Digital Certificate NETWORK SECURITY:  A complete layered strategy is required by modern  cybersecurity  methods, wherein many solutions cooperate to offer the highest level of protection against attackers. An essential component of this puzzle is digital certificates, which offer strong defense against manipulation and  man-in-the-middle attacks . VERIFICATION:  Digital certificates facilitate cybersecurity by restricting access to sensitive data, which makes authentication a crucial component of cybersecurity. Thus, there is a decreased chance that attackers will cause disturbance. At many different endpoints, certificate-based authentication provides a dependable method of identity verification. Compared to other popular authentication methods like biometrics or one-time passwords, certificates are more flexible. BUYER SUCCESS:  Consumers demand complete assurance that the websites they visit are reliable. Because digital certificates are supported by certificate authority that users’ browsers trust, they offer a readily identifiable indicator of reliability. Disadvantages of Digital Certificate Phishing Attacks:  To make their websites look authentic, attackers can fabricate bogus websites and obtain certificates. Users may be fooled into providing sensitive information, such as their login credentials, which the attacker may then take advantage of. Weak Encryption:  Older digital certificate systems may employ less secure encryption methods that are open to intrusions. Misconfiguration:  In order for digital certificates to work, they need to be set up correctly. Websites and online interactions can be attacked due to incorrectly configured certificates.

23. Certificate Authority and key management Kerberos