ect250surveyofe-commercetechnology

ect250surveyofe-commercetechnology内容摘要：

Medium: Safe but functional browsing。 prompts before downloading potentially unsafe content。 unsigned ActiveX will not be downloaded. • Mediumlow: Downloads everything with prompts。 most content will be run without prompts。 unsigned ActiveX will not be downloaded. • Low: Minimal safeguards。 most content will be downloaded and run without prompts。 all active content can be run. Security levels 33 • The Custom Level button allows you to alter the defaults provided by a specific level. • All protections are a choice between running and not running active content. • No monitoring of code occurs during execution. Security settings 34 • You can control whether active content (Java or Javascript) will be downloaded. • This is done using the Preferences dialog box. • On the Advanced tab you can specify what should be done for images, Java, JavaScript, style sheets, and cookies. • A message will be sent when Java or JavaScript is downloaded indicating whether the content is signed. A risk assessment is given. Netscape Navigator 35 Emerce security is best studied by examining the overall process, beginning with the consumer and ending with the merce server. This analysis produces a three part structure: 1. Client security 2. Communication channel security 3. Server security Outline 36 • The Inter was designed for redundancy, not secure munications. The DOD intended to encrypt all information moving in the work. • The Inter remains in its insecure state. • It is impossible to guarantee that every puter through which information passes is safe, secure, and nonhostile. • The possible security violations include secrecy, integrity, and necessity threats. Communication channel threats 37 • Email transmissions can be promised by the theft of sensitive or personal information. • Sniffer programs record information as it passes through a particular router. • This can capture: – Passwords – Credit card numbers – Proprietary corporate product information Sniffer programs 38 • An integrity threat is also called active wiretapping. • This occurs when an unauthorized party alters a message in a stream of information. • Cyber vandalism is the electronic defacing of an existing Web site’s page. This occurs when an individual replaces content on the site. • Masquerading or spoofing occurs when perpetrators substitute the address of their site for a legitimate site and then alter an order or other information before passing it along. Integrity threats 39 • Also known as delay or denial threats, the purpose is to disrupt or deny normal processing. • Slowing processing can render a service unusable. • The most famous example of a denial attack is the Robert Morris Inter Worm attack, perpetrated in 1988. Necessity threats 40 • Since the Inter is inherently insecure, any secret information must be encrypted. • Encryption is the coding of information using a program and a key to produce a string of unintelligible characters. • The study of encryption is called cryptography. The name es from krupto (secret) and grafh (writing). • Cryptography is not related to steganography. Encryption 41 • Unencrypted data is called plaintext. • Encrypted data is called ciphertext. • A key is a string of digits that acts as a password. • Only the intended receivers should have the key that transforms the ciphertext into plaintext. • A cipher or cryptosystem is a technique or algorithm for encrypting messages. • Cryptographic ciphers have a long history. Terminology 42 • Ciphers were used as far back as the ancient Egyptians. Text was encrypted by hand. • The two main types of ciphers were used: – Substitution cipher: Every occurrence of a given letter is replaced by a different one. Example: “a” by “b”, “b” by “c”, etc. “Uftujoh, uftujoh” – Transposition cipher: The ordering of the letters is shifted to form new words. Example: Plaintext = example Ciphertext = eape xml Early cipher systems 43 • Modern cryptosystems are digital。 the algorithms are based on the individual bits of a message rather than letters of the alphabet. • Computer information is stored as binary strings, sequences of 0’s and 1’s. • Encryption and decryption keys are binary strings of a given key length. Example: 128bit encryption systems. Modern cipher systems 44 • Someone can know the details of an encryption algorithm and yet not be able to decipher an encrypted message without the key. • The resistance of the encrypted message depends on the size, in terms of bits, of the key used in the encryption procedure. The longer the key, the more puting power and time it takes to break the code. Example: 128bit encryption systems. Knowledge needed 45 There are two main types of cryptosystems: • Privatekey cryptography Also known as symmetric or secretkey encryption, it uses a single key to both encrypt and decipher the message. • Publickey cryptography Also known as asymmetric encryption, it uses a public key to encrypt messages and a private key to decipher messages. Types of cryptosystems 46 Suppose that Alice wishes to send Bob a message: • They exchange a secret key. • Alice encodes the message using the secret key. • The ciphertext is sent to the Bob. • Bob decodes the message using the secret key. Problems with this approach: • How do Alice and Bob exchange the secret key? • There is no authentication of the sender. • What if both wish to municate with Chris? Privatekey cryptography 47 • A key distribution center shares a different key with each user in the work. • When Alice and Bob want to municate, they obtain a session key from the KDC. • They municate using the session key. • If Chris wants to municate。