Internet Security[1]

Internet Security Aspects of Security Privacy       sender and receiver expect confidentiality transmitted message must make sense only the intended receiver to all others, message must be unintelligible Plaintext: to be encrypted at the sender Ciphertext: encrypted data and will be decrypted at the receiver Encryption/decryption methods:   secret-key method public-key method Secret-key Encryption/Decryption   Same key is used by both parties -> key is shared <->symmetric encryption algorithms Algorithm used for decryption is the inverse of the algorithm used for encryption Advantages & Disadvantages  Advantages:   Take less time to encrypt a message Key is small -> used for long messages Each pair of users must have a secret key. N people -> need N(N-1)/2 secret keys. The distribution of the keys between two parties can be difficult -> Solution: using a third party KDC (Key Distribution Center) -> shares a key with both users  Disadvantages:   Public Key Encryption   a private key + a public key Private key:   is kept by receiver (individual) is used to decrypt ciphertext is announced to the public is used to encrypt plaintext  Public key:   Public Key Encryption Advantages & Disadvantages  Advantages:   Each entity is independent and the pair of keys can be used to communicate with any other entity. The number of keys needed is reduced tremendously <-> N users -> 2N keys The complexity of algorithm <-> using the long keys takes a lot of time -> just efficient for short messages The association between an entity and its public key must be verified (certification) -> solution: CA – Certification Authority  Disadvantages:   CA – Certification Authority   certify the binding between a public key and the owner (by issuing a certificate) How?    CA combine a public key and information about an entity into one document then CA encrypts the document with its private key and sends it to everyone registered to that authority the registered users can use their public key to decrypt the certificate and find the public key of the entity. Using the Combination    Secret key method: efficiency (long messages) Public key method: easy distribution of keys Combination:   Public key is used to encrypt the secret key Secret key is used to encrypt the message Using the Combination Digital Signature   To achieve authentication, integrity and non-repudiation Two choices:   Signing the whole document Signing the Digest Signing the Whole Document   Sender uses his private key to encrypt (sign) the message <-> his signature Receiver uses the public key of the sender to decrypt the message Digital Signature can provide integrity, authentication and non-repudiation -> How?    Integrity:  If an intruder intercepts the message and partially or totally changes it -> the decrypted message would be unreadable Authentication:  If an intruder (X) sends a message pretending that it is coming from someone else (G)  He must use his own private key for encryption (private X)  Message is then decrypted with the public key of G will therefore be unreadable  Encryption with X’s private key and decryption with G’s public key results in garbage Non-repudiation:  If sender denies sending the message, his private key corresponding to his public key can be tested on the original plaintext.  Digital signature does not provide Privacy. If there is a need for privacy, another layer of encryption/decryption must be applied Signing the Digest   Using public key to sign the entire message is very inefficient if message is very long -> signing a digest of the document instead of the whole document Operations:   Sender creates a miniature version (digest) of the document and signs it Receiver then checks the signature on the miniature Hash Function   To create a digest of the message -> using a hash function Hash function creates a fixed-size digest from a variable-length message Hash Function  Two most common hash function:   MD5 (Message Digest 5): 120-bit digest SHA-1 (Secure Hash Algorithm 1): 160-bit digest Hashing is one-way: the digest can only be created from the message, not vice versa One-to-one function: there is little probability that two messages will create the same digest  Two properties:   Signing the Digest – Operations at Sender site   After the digest has been created, it is encrypted (signed) using the sender’s private key The encrypted digest is attached to the original message and sent to receiver Signing the Digest – Operations at Receiver site    Receiver receives the original message and the encrypted digest Using the same hash function to the message to create the second digest Decrypts the received digest using the public key of the sender, then compares it with the second digest Digest is secure in terms of integrity, authentication and non-repudiation. But, what about the message itself?  Integrity:  Digest has not been changed and the digest is a replica of the message -> message has not been changed (NO two messages can create the same digest) If an intruder had initiated the message, the message would not created the same digest (NO two messages can create the same digest) Sender cannot deny the message since he cannot deny the digest  Authentication:   Non-repudiation:  Assignments (Course Project)     Group1: DES (Data Encryption Standard) Group2: RSA (A Public Key Method) Group3: MD5 Group4: SHA-1 Security in the Internet   Security measures can be applied to AL, TL, IPL App Layer:   each app is responsible for providing security simplest more complicated very complicated (security for both user apps and services to other protocols)  Trans Layer:   IP Layer:  Application Layer Security    used on Internet communication that involves only two parties sender and receiver can agree to use the same protocol and to use any type of security services they desire Two most common used protocols: PGP and SSH PGP – Pretty Good Privacy  Provides all four aspects of security (Email)   Integrity, authentication, and non-repudiation: using Digital Signature (combination of hashing and public-key encryption) Privacy: using a combination of secret-key and public-key encryption 1 hash function, 1 secret key, 2 private-public key pairs  Using:  PGP at the Sender site PGP at the Receiver site Transport Layer Security - TLS   Derived from SSL (Secure Socket Layer) For transactions on the Internet, a browser needs:     Customer needs to be sure that server belongs to the actual vendor, not an imposter -> authentication Customer needs to be sure that the contents of the message are not modified during transition -> integrity Customer needs to be sure that an imposter does not intercept sensitive information -> privacy so on… Position of TLS TLS = Handshake protocol + Data Exchange protocol  Handshake protocol: defines the exchange of a series of messages between browser and server.    negotiating security authenticating the server to browser defining other communication parameters (option)  Data Exchange protocol:   using the secret key to encrypt data secure and to encrypt the message digest for integrity details and specifications of algorithms is agreed upon during the handshake phase Handshake protocol TLS version & references Public key (certified by CA) encrypted with server public key encrypted by secret key • decrypts secret key using private key • decrypts message using secret key encrypted by secret key Security at the IP Layer IPSEC      providing security for a packet carried on the Internet NOT defining the use of any specific encryption or authentication method providing a framework and a mechanism leaving the selection of the encryption, authentication and hashing methods to the user Two protocols used at IP (network layer): Authentication Header (AH) and Encapsulating Security Payload (ESP). Authentication Header - AH   providing Integrity: involves a digital signature using a hashing function Message digest (created by applying the hashing function) is included in AH header, and inserted between the IP header and transport layer data and header AH Header Format Length of AH Type of Payload carried by IP datagram Security method Result of applying a hash function to the entire IP datagram Ordering information for a sequence of datagram Addition of an AH header 1. 2. 3. 4. An AH header is added to Payload with authentication data field set to 0 The AH header and Payload are hashed to create the authentication data The authentication data are inserted into the AH header The IP header is added after changing the value of the protocol field to 51 Encapsulating Security Payload - ESP Privacy AH ESP No Yes Integrity and message authentication Yes Yes ESP Procedure 1. 2. 3. 4. 5. 6. An ESP trailer is added to Payload The Payload and the trailer are encrypted The ESP header is added The ESP header, Payload, and the ESP trailer are used to create authentication data The authentication data are added at the end of the ESP trailer The IP header is added after changing the protocol value to 50 ESP – Format of Header and Trailer Firewalls   A router installed between the internal network of an organization and the rest of the Internet. Forwarding some packets and filter others  Two types (based on specific purposes)   Packet-filter Firewall Proxy-based Firewall Packet-Filter Firewall  Forward or block packets based on the information in:    network layer header: source, destination IP addresses transport layer header: source, destination Port addresses type of protocol (TCP or UDP)  using a Filtering Table to decide which packet must be discarded Filtering Table Proxy Firewall  Filter a message based on the information available in the message itself (at application layer)