SEEM4540 Open Systems for E-Commerce Lecture 03 Internet Security

Transcription

1 SEEM4540 Open Systems for E-Commerce Lecture 03 Internet Security

2 Consider 2. Based on DNS, identified the IP address of is Go to 3. Forward the request User computer ISP Provider (CUHK Server) 5. Forward the reply to the user 4. Reply from cuhk server NOTE: He knows EVERYTHING!

3 What if 2. Based on DNS, identified the IP address of Store X ( is xx.xx.xx.xx 1. Send the Credit Card information to Store X via 3. Forward the request, which includes Credit Card Information User computer ISP Provider xx.xx.xx.xx 5. Forward the reply 4. Reply NOTE: He knows EVERYTHING including the Credit Card information!

4 In Addition ISP Provider User computer ISP Provider xx.xx.xx.xx NOTE: Everyone along the line knows everything!

5 So To avoid any people except the target recipient can understand our data, we need encryption. Technically, we cannot prevent people reading our data. We need to rely on ISP to help us forward our data. But we can only prevent people from understanding the data even if they read it. E.g. Encode the data Solution: SSL.

6 SSL If you re serious about doing business online, you need SSL. It s the best way to protect user data and defend against identity theft and man-in-the-middle attacks. It is theoretically impossible to sniff or modify the data as it travels down the wire. Many customers will refuse to do business with a website that doesn't have SSL. Displaying your SSL Site Seal tells customers they can shop with confidence, knowing they're protected. Different certificates provide different levels of validation.

7 SSL in Action 1. The user send the Credit Card information to Store X via 2. The browser detected that the url begins with https 4. Based on DNS, identified the IP address of Store X ( is xx.xx.xx.xx Note: the credit card information is not sent y 3. The browser sends a request to for establishing a secure connection without sending the credit card information 5. Forward the request that the browser wants to establish a secure connection. User computer ISP Provider xx.xx.xx.xx

8 SSL in Action (cont d) User computer ISP Provider xx.xx.xx.xx 7. Forward the reply 6. Reply its SSL Certificate. A SSL Certificate contains a public key 8. The browser checks if the SSL Certificate is valid. It will notify the user if the certificate is invalid. 9. If everything is fine, the browser then generate a session key 10. The browser encrypt the session key using the public key in the SSL Certificate

9 SSL in Action (cont d) 11. The browser sends the encrypted session key 12. The server tries to decrypt the encrypted session key with its private key (a private key can decrypt messages that are encrypted by a public key). User computer ISP Provider xx.xx.xx.xx 14. Forward the reply. 13. If the decryption can be done successfully, then the server will reply the user everything is correct. Note that even in this simply reply, it is encrypted with the session key.

10 SSL in Action (cont d) 15. The browser decrypt the message using the session key and knows everything is OK. It then encrypt everything (e.g. credit card information) using the session key now. 16. The encrypted data (credit card information) is sent now. Since it is encrypted, the ISP cannot understand the data. 17. Forward the request (the encrypted data) User computer ISP Provider xx.xx.xx.xx NOTE: He cannot understand the data because it is encrypted! (i.e. he knows nothing!) 18. Decrypt the data using session key and obtain the credit card information

11 SSL in Action (cont d) There are three keys involved: Public key (distribute by the server) An asymmetric key that works with private key. Used for encrypting the session key (step 9). Private key (stored inside the server. Never distribute) An asymmetric key that works with public key. Used for decrypting the session key (step 12). Must store in a safe place. Session key (generate by client) A symmetric key. Only generate once per session. Only exchange in handshaking (step 9 15)

12 SSL Certificates SSL Certificates are small data files that digitally bind an encryption key to an organization s details. When installed on a web server, it activates the https protocol (over port 443 by default) and allows secure connections from a web server to a browser. We will talk more about port later. Some important information that a SSL Certificate contains A domain name. An organizational identity (i.e. company name) and location. An encryption algorithm (the method used to encrypt the data) An encryption key called public key

13 SSL Certificates (cont d) The structure of SSL Certificate follows X.509 standard: Certificate Version Serial Number Algorithm ID Issuer Validity Not Before Not After Subject Subject Public Key Info Public Key Algorithm Subject Public Key Issuer Unique Identifier (optional) Subject Unique Identifier (optional) Extensions (optional)... Certificate Signature Algorithm Certificate Signature

14 SSL Certificates (cont d) Previously: User computer The browser try to check if the domain name written inside the certificate is the same as the domain name you are requesting. E.g., if the domain you are requesting is but the domain name written in the certificate is cuhk.edu.hk, then it is invalid (even a character different is not tolerant). 8. The browser checks if the SSL Certificate is valid. It will notify the user if the certificate is invalid.

15 SSL Certificates (cont d)

16 A Self-Signed Certificate If you are using Linux or Mac, open a terminal and type the followings (if you are using Windows, you need to install openssl): Generate some keys: openssl genrsa -des3 -passout pass:x -out server.pass.key 2048 openssl rsa -passin pass:x -in server.pass.key -out server.key Remove passphrase (so when you restart Apache, it will not ask you a password to read the certificate): rm server.pass.key Generate a self-sign request: openssl req -new -key server.key -out server.csr Generate a certificate which follows X.509 standard: openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

17 How to Obtain a SSL Certificate? Since SSL Certificate is just a small piece of data, everyone can generate one! E.g. It is possible that someone generated a SSL Certificate, installed on his own web server, and then claim that his web server is the official CUHK web server but in fact it is NOT! To avoid the above problem (at least warn the user), we need to have a third-party to valid our identity. Certificate authority (CA) Using Digital Signature (we will talk about it soon)

18 Certificate Authority In cryptography, a certificate authority or certification authority (CA) is an entity that issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. As we ask someone to verify our identity, we need to pay them back That s why SSL Certificate cost money Quick question: Can I open a company and become a CA? Answer: Yes. Yet, who trust you

19 Level of Certification Depends on the amount of information you want to disclose to the CA, the level of trust you want your clients feel, your purpose, etc, you can purchase different kinds of SSL Certification: Domain SSL Certification Extended Validation SSL Certification Wild Card SSL Certification Multi-Domain SSL Certification

20 Domain SSL vs. Extended Validation SSL

21 Wild Card SSL Remember that in the previous example: If the domain you are requesting is but the domain name written in the certificate is cuhk.edu.hk, then it is invalid. In e-commerce, we always have many sub-domain. It is sometimes impossible to know all sub-domain in advance at the time we purchase the SSL Certificate. Hence, Wild Card SSL appears. E.g., *.cuhk.edu.hk

22 Multi-Domain SSL It is also know as SANs (Subject Alternative Names) SSL Certificate. Technically, one IP Address can install one SSL Certificate only In practice, we usually host many web sites in one single server with one single IP address. Multi-domain SSL can protect a number of domain names in one certificate. Limitations: Usually can put up to 100 domain names. Need to re-issue the certificate once a new domain name is added. The re-issuing process is well

23 Encryption Algorithm Asymmetric encryption algorithm. There are two keys. One is encryption key and the other one is decryption key. The encryption key can only be used for encryption. The decryption key can only be used for decryption. Theoretically, it is impossible to derive the encryption key from the decryption key, and vice versa. A Secret Message + A Key Generation Algorithm Private Key Public Key

24 Encryption Keys The public key can distribute to any people. Common usages: Encrypt the information sent over the Internet Verify a digital signature The private key should be stored in a very secure place and never distribute to anyone. Common usage: Decrypt the information received from the Internet Create a digital signature

25 Encryption Keys (cont d) What exactly are the pair of encryption keys looks like? You can try to generate a pair of encryption keys easily if you are using Linux or Mac. If you are using Windows, you need to install software like OpenSSL. To generate a pair of keys, in a terminal, type: ssh-keygen -f mykeyname.key

26 Encryption Algorithm and Keys Putting all together:? Plain text Public Encryption Key Cipher text Private Decryption Key Plain text As it is impossible to derive the private key from the public key, it should be safe even if the encrypted data is being read. To decrypt the data other than the target server, one would need to have a copy of the server s private key by stealing it from the target server. While this is not impossible, it is very unlikely to happen.

27 Digital Signature A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or document. We talked about Digital Signature on P.17 A valid digital signature gives a recipient reason to believe that the message was created by a known sender, such that the sender cannot deny having sent the message (authentication and non-repudiation) and that the message was not altered in transit (integrity).

28 Create a Digitally Signed Certificate Creating a digital signature and a digitally signed data 3. Combine them Server certificate 1. The CA apply a Hash Algorithm (e.g. MD5) Digitally Signed Certificate A Hash Code ( bits) 2. The CA apply his Private Key Digital Signature It is signed by the CA now

29 Verify a Digitally Signed Certificate Extract A Hash Code ( bits) Digital Signature Public Key Decryption (obtained from the trusted CA in the browser) Compare if they are the same? Digitally Signed Certificate Apply a Hash Algorithm based on the trusted CA in the browser Server certificate A Hash Code ( bits)

30 Create a Digitally Signed Data A more general overview: 3. Combine all three of them Plain Text 1. Apply a Hash Algorithm (e.g., MD5) Digitally Signed Data A Hash Code ( bits) Digital Signature 2. Apply the Private Key Digital certificate

31 Verify a Digitally Signed Data Extract A Hash Code ( bits) Digital Signature Public Key Decryption (obtained from the digital certificate) Digitally Signed Data Digital certificate Apply a Hash Algorithm based on the digital Certificate A Hash Code ( bits) Compare if they are the same? Plain Text

32 Questions Can a coffee shop monitor my traffic over their network if I am using my computing devices (e.g. mobile, labtop)? No. The magic of public-key cryptography means that an attacker can watch every single byte of data exchanged between your client and the server and still have no idea what you are saying to each other except roughly how much data you are exchanging. Can a coffee shop monitor my traffic over their network if I am using their computing devices? Yes, (although probably won t). Can you think about how?

33 FTPS SSL can be used in a number of other scenarios, including FTPS. Note: Instead of using FTP (no encryption), try to use FTPS Don t confuse FTPS with SFTP. FTPS, like HTTPS, is based on SSL Certificate. On the other hand, SFTP is based on another technology called SSH.

34 SSH Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers. Default port is 22 (SSL is 489) No digital certificate is involved. It is usually used for secure data transfer between two known parties.

35 SSH Vulnerabilities On December 28, 2014 Edward Snowden suggests that the US National Security Agency (NSA) is able to decrypt certain SSH traffic, though the technical details associated with this attack were not released yet so far.

36 References Books: URL: Behrouz A. Forouzan. Data Communications and Networking. McGraw Hill. 4th Edition James F. Kurose and Keith W. Ross. Computer Networking. Addison Wesley. 3rd Edition