EECS 122 University of California Berkeley Examples of Attack Principles Threats Cryptography Security Systems EECS122 Contents Index SECURITY Buffer Overflow Denial of Service Attack Email virus ARP attack EECS122 Contents Index SECURITY Attacks Basic Mechanism Attacker overwrites program stack to force execution of her code Examples Virus Corrupt files EECS122 Contents Index SECURITY Attacks Buffer Overflow 0 1 EECS122 Contents Index SECURITY Attacks Buffer Overflow Protect memory by preventing overwrite of stack either through OS or through language Check validity of request EECS122 Contents Index SECURITY Attacks Buffer Overflow Basic Mechanism Flood a host with a rapid sequence of SYNs Effect Host sets aside some space to store state of new TCP connection If rapid sequence then host runs out of space and crashes Remedies Check for valid SYNs i e SYNs followed by requests discard invalid SYNs to clear memory Use smart firewall that forwards only valid SYNs to hosts Store state in cookie that comes back with request EECS122 Contents Index SECURITY Attacks DOS SYN Distributed Denial of Service Attack Basic Mechanism Saturate a link to a host by sending requests from many nodes across the Internet Effect Host is incapacitated Remedies Verify that source IP exists i e is not spoofed Block packets that DDOS tools use some ICMPs Limit rate of ICMP flows Limit rate of SYNs Trace back from last router upstream to block packets toward that link EECS122 Contents Index SECURITY Attacks DOS DDOS Basic Mechanism Attachment that contains virus Effect Some email programs execute code in virus without authorization Remedies Firewall to check attachments and remove specific ones Avoid automatic execution of attachments EECS122 Contents Index SECURITY Attacks Email Basic Mechanism Intruder replies to ARP request and performs denial of service on host A ARP Who is IP B C ARP I am IP B DoS B Effect C impersonates B for A Remedies Check source of ARP Avoid DoS EECS122 Contents Index SECURITY Attacks ARP You would somehow like to have your data or that of others be secure This often means you want to know who really sent it know nobody else read it More specifically protect from eavesdropping masquerading replay traffic analysis exploit based attacks denial of service EECS122 Contents Index SECURITY Principles These attacks are often classified as Active somebody actually generates or modifies network traffic easier to detect harder to prevent Passive somebody just collects and analyses network traffic harder to detect easier to prevent EECS122 Contents Index SECURITY Principles 01 Against Type Protection Computers Physical Infection Intrusion Physical security lock Virus detection Firewall passport control Users Identity Privacy Signature password watermark Encryption relay Documents Integrity Confidentiality Message authentication code Encryption EECS122 Contents Index SECURITY Threats 2 1 Basic Mechanism Main Issues Secret Key Public Key Hashing EECS122 Contents Index SECURITY Cryptography 3 1 2 345 2 2 645 2 6 7 7 4 3 7 5 3 7 EECS122 Contents Index SECURITY Cryptography Basic Mechanism 3 1 345 8 9 645 Two flavors Secret Key E and D are known only to Bob and Alice Public Key Alice advertises E that should be used to encrypt messages to her EECS122 Contents Index SECURITY Cryptography Basic Mechanism 3 1 2 345 2 2 645 2 645 345 345 9 0 2 7 1 3 7 2 345 9 2 7345 9 645 2 7 4 345 5 9 645 EECS122 Contents Index SECURITY Cryptography Basic Mechanism 3 For the cryptographer the main issues choice of the transformation D and E is the underlying mathematical basis efficient for decoding and encoding with keys and hard without them do you publish the algorithm or not generation and distribution of keys might like to use random numbers but computers aren t exactly random devices how do you get a secret from one person to another if you don t already have keys EECS122 Contents Index SECURITY Cryptography Main Issues 3 For the cryptanalyst the main issues what is already known algorithm plaintext ciphertext pairs any information about generation of the keys types of attacks ciphertext only freq analysis brute force known plaintext chosen plaintext EECS122 Contents Index SECURITY Cryptography Main Issues 4 345 34 5 645 64 5 34 5 EECS122 Contents Index 7 9 8 9 64 5 SECURITY Cryptography Secret Key 4 EXAMPLE 1 One Time PAD C P K addition bit by bit modulo 2 no carry K random string of bits 50 0 50 1 If used only once this is a perfect code C is perfectly random and contains no information about P Application Top Secret transmissions K is stored in a CD ROM that is delivered securely ahead of time EECS122 Contents Index SECURITY Cryptography Secret Key 4 EXAMPLE 2 Data Encryption Standard DES 7 63 9 7 9 AB9 C 9 EECS122 Contents Index SECURITY Cryptography Secret Key 4 Note DES Modes of Encryption 64 bits 64 bits E 64 bits 64 bits 64 bits E 64 bits Rn 1 Cn 1 n 1 RC n 1E E Pn R Pn R n EC D Pn Pn n n Z Zn 1 P Pn n 1 Cn n Cn EECS122 Contents Index SECURITY Cryptography Secret Key 4 Note DES Modes of Encryption 64 bits 64 bits E 64 bits 64 bits 64 bits E 64 bits Rn 1 Cn 1 n 1 RC n 1E E Pn R Pn R n EC D Pn Pn n n Z Zn 1 P Pn n 1 Cn n Cn EECS122 Contents Index SECURITY Cryptography Secret Key 4 Note DES Modes of Encryption 64 bits 64 bits E 64 bits 64 bits 64 bits E 64 bits Rn 1 Cn 1 n 1 RC n 1E E Pn R Pn R n EC D Pn Pn n n Z Zn 1 P Pn n 1 Cn n Cn EECS122 Contents Index SECURITY Cryptography Secret Key 5 4 3 2 8 9 34 8 95 78 9 64 8 95 2 7 2 D 42C5 42C5 C D E C 2CF G G 4 5 9 4 5 4 5 9 9 EECS122 Contents Index SECURITY Cryptography Public Key 6 1 2 45 4 CB 9 5 EECS122 Contents Index H SECURITY Cryptography 45 4H 5 Hashing Integrity Key Management Identification EECS122 Contents Index SECURITY Cryptography Systems 2 Alice sends P H P where H P is protected by a Authentic channel b Message Authentication Code Note that E H P K with K secret may not be secure For instance Z H P R is not secure since then Eve can compute H P from P and R from Z H P and then Eve can send P and H P R Secure H K2 H K1 P where K1 and K2 are secret to Alice and Bob since Eve cannot compute H K1 P EECS122 Contents Index SECURITY Cryptography Systems Integrity 2 Alice sends P H P where H P is protected by c Digital Signature Alice sends C D P Alice and Bob recovers P E C Alice However if Eve constructs C and computes P E C Alice Bob will think that Alice sent D P Alice Instead Alice should send D P H …
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