Introduction to Cryptography and digital signatures
- 1. Cryptography
- 2. Cryptography • Cryptography is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. • The word ‘cryptography’ was invented by combining two Greek words, ‘Krypto’ meaning hidden and ‘graphene’ meaning writing. • The art and science of concealing (hiding) the messages to introduce secrecy in information security is recognized as cryptography.
- 3. Cryptography Plaintext= means the message Encryption=encoding(hidin g the contents from outsiders) the message Ciphertext= the encrypted message Decryption=the process of retrieving the plaintext from the ciphertext “Encryption” and “Decryption” makes use of a “key and a coding method”.
- 4. Encryption techniques There are three important encryption techniques now in use: • Symmetric or “private key” encryption • Asymmetric or “public key” encryption • Digital signature, which are based on a variation of public key encryption.
- 5. Symmetric-key systems use a single key that both the sender and recipient have, and public-key systems use two keys, a public key known to everyone and a private key known only to the recipient of messages.
- 7. • The illustration shows a sender who wants to transfer some sensitive data to a receiver in such a way that any party intercepting or eavesdropping on the communication channel cannot extract the data. • The objective of this simple cryptosystem is that at the end of the process, only the sender and the receiver will know the plaintext.
- 8. • Components of a Cryptosystem: • The various components of a basic cryptosystem are as follows: • Plaintext: It is the data to be protected during transmission. • Encryption Algorithm: It is a mathematical process that produces a cipher-text for any given plaintext and encryption key. It is a cryptographic algorithm that takes plaintext and an encryption key as input and produces a cipher-text.
- 9. • Cipher-text: It is the scrambled version of the plaintext produced by the encryption algorithm using a specific the encryption key. The cipher-text is not guarded. It flows on public channel. It can be intercepted or compromised by anyone who has access to the communication channel. • Decryption Algorithm: It is a mathematical process, that produces a unique plaintext for any given cipher-text and decryption key. It is a cryptographic algorithm that takes a cipher-text and a decryption key as input, and outputs a plaintext. The decryption algorithm essentially reverses the encryption algorithm and is thus closely related to it.
- 10. • Encryption Key: It is a value that is known to the sender. The sender inputs the encryption key into the encryption algorithm along with the plaintext in order to compute the cipher-text. • Decryption Key: It is a value that is known to the receiver. The decryption key is related to the encryption key, but is not always identical to it. The receiver inputs the decryption key into the decryption algorithm along with the cipher-text in order to compute the plaintext.
- 16. Symmetric Algorithm • Data Encryption Standard(DES) is a symmetric algorithm developed by IBM and maintained by the National Institute of Standard and Technology. It is base on encryption multiple times with different keys. A 56-bit version of DES is commonly used, but can be broken by brute force. Other Symmetric encryption techniques include: • RC4 uses a 40 bit key, but can use up to 256 bits. • Triple DES(3DES) used DES three times, effectively giving it a 168 bit key. • Advance Encryption Standard(AES), design to replace DES uses 128,192, and 256 bit keys.
- 17. Digital Signature An electronic and Digital Signatures • Authenticates the identity of the sender of a message, or the signer of a document • Or ensures that the contents of a message are intact. Digital Signatures features: • Are easily transportable • Cannot be imitated by someone else • And can be automatically time-stamped • The ability to ensure that the original signed message arrived means that : • the sender can not easily repudiate it later.
- 18. Digital Signatures • Sender encrypts message with their private key • Receiver can decrypt using sender public key • The authenticates sender, who is only person who has the matching key. • Does not give “privacy” of data • decrypt key is public https://youtu.be/JR4_RBb8A9Q
- 19. Digital Signatures • Digital Signatures are a cryptographic technique and are one of the most important application of asymmetric public-key cryptography. • They are electronic or digital signature that can be used to authentication the identity of the sender of the message or the signer of the document(to ensure that content of the sent message unchange) . • A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software or digital document.
- 20. Digital Signatures • The Digital Signature, is a small part of message, and includes: • The name of the sender • Other key contents • The Digital Signature in the outgoing message is encrypted using the sender’s private key. • The Digital Signature is then decrypted using the sender’s public key thus providing evidence that the message originate from the sender. • Digital Signature and public key encryption combine to provide secure and authentication message transmission.
- 21. Digital Signatures-How? Sender 1. Create a message 2. Hash the message to product a message digest 3. Encryption the message digest with sender’s private key 4. Append the encrypted digest to the message 5. Send message Recipient 1. Receive message 2. Decrypt the message digest with the sender’s public key 3. If this work’s the sender is authenticated 4. Hash the message to produce another message digest 5. Compare message digest in step 2 with step 4. if the same , the message has been changed.
- 23. Certificate Authority • Certificates are usually tied to a particular domain. They can be issued by a central entity, called a Certificate Authority (CA), or created and signed locally. • The biggest organization is VeriSign, the company that also runs the domain names system. They have sanctioned many other companies to offer certificates under their authority. • Generally, the organization will not issue a certificate until they verify the information you are putting in the certificate, either by phone or via some kind of paper documentation.
- 24. Certificate Authority • Once they "certify" you, they will take this information, including the URLs you are going to use the certificate for, and digitally "sign" it by encrypting it with their private key. Then a Web server or other program can use this certificate. When outside users receive some data, such as a Web page from the server, and it has a certificate attached, they can use public key cryptography to decrypt the certificate and verify your identity.