Introduction to Cryptography
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The document provides a comprehensive overview of cryptography, covering key concepts such as encryption, decryption, and various types of cryptographic techniques including symmetric and asymmetric algorithms, as well as hashing and digital signatures. It details the general goals of cryptography such as confidentiality, integrity, authentication, and nonrepudiation, along with common types of attacks against cryptographic systems. Furthermore, the document discusses important protocols like Transport Layer Security (TLS) and Public Key Infrastructure (PKI), highlighting their roles in secure communication.
![Common Symmetric Algorithms
DES
Designed by IBM in the 1970s and
adopted by the National Institute for
Standards and Technology (NIST)] in
1977 for commercial and unclassified
government applications.
DES is a block-cipher employing a 56-
bit key that operates on 64-bit blocks.
DES results in a permutation among
the 264 possible arrangements of 64
bits, each of which may be either 0 or 1
Triple DES (3DES) is an enhanced
version of DES which applies the Data
Encryption Standard (DES) cipher
algorithm three times to each data
block.
AES
AES was announced by National
Institute of Standards and Technology
on November 26, 2001.
AES is a block cipher with a block
length of 128 bits.
It allows for three different key lengths:
128, 192, or 256 bits.
Encryption consists of 10 rounds of
processing for 128-bit keys, 12 rounds
for 192-bit keys, and 14 rounds for 256-
bit keys.](https://image.slidesharecdn.com/introductiontocryptography-170212171141/85/Introduction-to-Cryptography-12-320.jpg)
Introduction to Cryptography
- 1. S E E M A G O E L g o e l s e e m a 1 1 @ g m a i l . c o m Introduction to Cryptography
- 2. Contents Basic Terms Cryptography The General Goals of Cryptography Common Types of Attacks Substitution Ciphers Transposition Cipher Steganography- “Concealed Writing” Symmetric Secret Key Encryption Types of Symmetric Algorithms Common Symmetric Algorithms Asymmetric Secret Key Encryption Common Asymmetric Algorithms Public Key Cryptography Hashing Techniques Hashing Algorithms Digital Signatures Transport Layer Security Public key infrastructure (PKI)
- 3. Basic Terms Encryption Scrambling a message or data using a specialized cryptographic algorithm. Plaintext The message or data before it gets encrypted. Ciphertext The encrypted version of the message. Cipher The algorithm that does the encryption. Decryption The process of converting ciphertext back to the original plaintext.
- 4. Cryptography Cryptography is the study of " Secret (crypto-) writing (-graphy) It can be described as the study of protecting information weather in transit or at rest, by using techniques to render the information unusable to anyone who does not possess the means to decrypt it. Cryptanalysis is the science of recovering the plaintext from the ciphertext without access to the key. Plaintext Ciphertext Plaintext Encryption Decryption
- 5. The General Goals of Cryptography Confidentiality Assuring that only authorized parties are able to understand the data. Integrity Ensuring that when a message is sent over a network, the message that arrives is the same as the message that was originally sent. Authentication Ensuring that whoever supplies or accesses sensitive data is an authorized party. Nonrepudiation Ensuring that the intended recipient actually received the message & ensuring that the sender actually sent the message.
- 6. Common Types of Attacks Ciphertext-Only Attack Known-Plaintext Attack Chosen-Plaintext Attack Chosen-Ciphertext Attack Dictionary Attacks
- 7. Substitution Ciphers Caesar’s Cipher A B C D E F G H I J K L . . . . . . . . X Y Z A B C D E F G H I J K L . . . . . . . Atbash Cipher A B C D E F G H I J K L . . . . . . . . Z Y X W V U T S R Q P O. . . . . . . Vigenere Cipher Polyalphabetic cipher to overcome the shortcomings of simple substitution ciphers Plaintext Caesar’s alphabet Plaintext Atbash’s alphabet ATTACKATDAWN……… LEMONLEMONLE…….. LXFOPVEFRNHR………. Plaintext Key Ciphertext
- 8. Transposition Cipher In a transposition cipher, permutation is used, meaning that letters are scrambled. The key determines the positions that the characters are moved to. Simple substitution and transposition ciphers are vulnerable to attacks that perform frequency analysis. example text examp letex 24153 31524 xmepa tlxee Message Broken into groups Key Ciphertext
- 9. Steganography- “Concealed Writing” It is the art and science of writing hidden messages in an object(wave file, graphic, audio or video) in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message. The least significant bit of each byte of the image can be replaced with bits of the secret message. Example of still imagery steganography. Left hand side image is the original cover image, where as right hand side does embedding a text file into the cover Image make the stego image. The advantage of steganography, over cryptography alone, is that messages do not attract attention.
- 10. Symmetric Secret Key Encryption With this approach the sender and the receiver use the same secret key to encrypt and decrypt messages. The strength of symmetric key encryption is fast, bulk encryption. Major Challenges Key distribution- It requires a secure mechanism to deliver keys properly. Scalability- Each pair of users needs a unique pair of keys, so the number of keys grow exponentially Examples of symmetric algorithms are as follows: DES (Data Encryption Standard) 3DES AES (Advanced Encryption Standard)
- 11. Types of Symmetric Algorithms Block Cipher Operate by encrypting a fixed amount, or “block,” (64 or 128 bit) of data It is somewhat faster than stream cipher each time n characters executed. Transmission errors in one cipher text block have no affect on other blocks. Identical blocks of plaintext produce identical blocks of cipher text. Block encryption may be more susceptible to cryptanalysis than either stream mode. Stream cipher Treats the message as a stream of bits or bytes and performs mathematical functions on them individually The same plaintext bit or byte will be transformed into a different ciphertext bit or byte each time it is encrypted Stream cipher is less vulnerable to insertion or deletion. Transmission error at the nth bit in the stream cipher may lead to incorrect ciphertext thereafter.
- 12. Common Symmetric Algorithms DES Designed by IBM in the 1970s and adopted by the National Institute for Standards and Technology (NIST)] in 1977 for commercial and unclassified government applications. DES is a block-cipher employing a 56- bit key that operates on 64-bit blocks. DES results in a permutation among the 264 possible arrangements of 64 bits, each of which may be either 0 or 1 Triple DES (3DES) is an enhanced version of DES which applies the Data Encryption Standard (DES) cipher algorithm three times to each data block. AES AES was announced by National Institute of Standards and Technology on November 26, 2001. AES is a block cipher with a block length of 128 bits. It allows for three different key lengths: 128, 192, or 256 bits. Encryption consists of 10 rounds of processing for 128-bit keys, 12 rounds for 192-bit keys, and 14 rounds for 256- bit keys.
- 13. Asymmetric Secret Key Encryption Asymmetric encryption uses a key pair (Public key and Private key) . The two different asymmetric keys are mathematically related but cannot be derived from each other. Each key type can be used to encrypt and decrypt. If data is encrypted with a private key, it must be decrypted with the corresponding public key and vice versa. Better key distribution and scalability than symmetric systems. Works much slower than symmetric systems. Examples of asymmetric key algorithms: RSA Elliptic Curve Cryptosystem (ECC)
- 14. Common Asymmetric Algorithms RSA (Ron Rivest, Adi Shamir and Leonard Adleman) Developed in 1978 at MIT RSA gets its security from the difficulty of factoring large numbers Best known & widely used Each user generates a public/private key pair by applying the RSA algorithm to two large primes at random say p and q One advantage of using RSA is that it can be used for encryption and digital signatures RSA is used in many Web browsers with the Secure Sockets Layer (SSL) protocol
- 15. Common Asymmetric Algorithms (contd.) Elliptic Curve Cryptosystems (ECCs) ECC was introduced by Victor Miller and Neal Koblitz in 1985 For elliptic-curve-based protocols, it is assumed that finding the discrete logarithm of a random elliptic curve element with respect to a publicly known base point is infeasible The size of the elliptic curve determines the difficulty of the problem. ECC requires significantly smaller key size with same level of security as compared to the key size for RSA : faster computations, need less storage space ECC ideal for constrained environments : Pagers , PDAs , Cellular Phones and Smart Cards
- 16. Public Key Cryptography It is a hybrid use of two different algorithms: asymmetric and symmetric Public key cryptography uses two keys (public and private) generated by an asymmetric algorithm for protecting encryption keys and key distribution, and a secret key is generated by a symmetric algorithm and used for bulk encryption. Bill sends a message
- 17. Hashing Techniques Cryptographic hashing functions are used to ensure the integrity of data using an integrity checksum. Hashing functions are one-way functions. This means that the ciphertext (i.e., the checksum) cannot be used to reconstruct the plaintext. The checksum (the ciphertext) is much smaller than the plaintext. Hashing functions provide a kind of digital fingerprint. The security of the hashing function is related to the size of the resulting checksum (in bits) Examples of Hashing Algorithms: MD5 (Message-Digest algorithm 5) SHA (Secure Hash Algorithm)
- 18. Hashing Algorithms MD5 128- bit hash value typically expressed as a 32-digit hexadecimal number. MD5 processes a variable-length message into a fixed-length output of 128 bits. It is easy to compute. It is infeasible to modify a message without changing its hash. No two messages have the same hash. SHA SHA-1 produces a 160-bit hash value. SHA-256 uses 32-bit words. SHA-512 uses 64-bit words. The collision ratio for SHA is far less than the collision ratio MD5.
- 19. Digital Signatures Goals Itshould be proof of authenticity and should be impossible to forge. It should be impossible to alter the signed document without detection. It should be impossible to transplant the signature to another document. Technology A hash function to help generate the digital signature, S. Symmetric (secret key) cryptography to encrypt the message, M. Public key cryptography to share the secret key used to encrypt and decrypt the message, M. Public key cryptography to encrypt and decrypt the digital signature, S.
- 20. Transport Layer Security It provides communication security over the Internet. Encrypt the segments of network connections at the Application Layer using asymmetric cryptography for key exchange, symmetric encryption for privacy, and message authentication codes for message integrity. Widespread use in applications such as web browsing, electronic mail, Internet faxing, instant messaging etc. The TLS protocol is made up of two layers. The record protocol is designed to protect confidentiality The handshake protocol allows authentication TLS is application protocol-independent. A vulnerability (CVE-2011-3389) was reported in The SSL protocol which allows attackers to obtain plaintext HTTP headers via a blockwise chosen- boundary attack on an HTTPS session.
- 21. Public key infrastructure (PKI) It consists of programs, data formats, procedures, communication protocols, security policies, and public key cryptographic mechanisms working in a comprehensive manner to enable a wide range of dispersed people to communicate in a secure and predictable fashion. PKI is an ISO authentication framework that uses public key cryptography and the X.509 standard protocols PKI provides authentication, confidentiality, nonrepudiation, and integrity of the messages exchanged PKI is a hybrid system of symmetric and asymmetric key algorithms Each person who wants to participate in a PKI requires a digital certificate
- 22. Thank You!!