02. Malware (10 points) In accepting the ACM Turing Award, Ken Thompson described a devious Trojan horse attack ona Une system, which most people now refer to as Thompson's rigged compiler. This attack changes the binary version of the login program to add a backdoor, say to allow a newnes, 12345, that has password, 67890, which is never checked against the password. Thus, the attacker can always login to this computer using this usemame and password. Then the attack changes the binary version of the compiler, so that it checks d it is coming the source code for the login program, and, if so, it reinserts the backdoor in the binary version. This system administrator cannot remove this Trojan horse simply by recompiling the log program na the attack goes a step further so that the compler also check it is compiling the source code of the compiler itself, and if so, it inserts the extra code that seinerts the backdoot for when st is compiling the login program. So recompiling the compiler won't remove this attack either, and if anyone examines the source code for the login program or the compiler, they won't notice that anything is wrong. Now suppose your une system has been comprised in this way (which you confirm by logging in as 123451. How can you fix it, without using any outside resources like a fresh copy of the operating systemi? 2.3 Encryption (40 points) Answer the following short questions 2. Caesar Cipher: Julius Caesar is about to invade Britain again and he send an encrypted message to one of his top commanders in the area that is now known as Cardiff Wales Unfortunately for fortunately depending on how you look at this messages intercepted by an intrepid band of Britons and they come to you asking for helpin decrypting the message. Here is the encrypted test: (15 points) DWWDFNDWGDZA Use your knowledge that this message was encrypted using a Casatopher with a shift of help these poor Britons decipher Caesar's message After deciphering the message the Britons decide to send back an impudent message to the despot Caesar. They ask you to encrypt the message GOBACITOROMEYOUIERK Using the same cipher that Caesar used what cipher test should be output to match this plaintext? b. What are the next three numbers in the pseudo-random number generator 3*2 mod 11 starting from 5? (5 points 4. Show the result of encrypting Musing the public keyle 3.77) in the SA cryptosystem (5 points) 22. Malware (10 points) In accepting the ACM Turing Award, Ken Thompson described a devious Trojan horse attack on a Unix system, which most people now refer to as Thompson's rigged compiler. This attack changes the binary version of the login program to add a backdoor, say, to allow a new user, 12345, that has password, 67890, which is never checked against the password. Thus, the attacker can always login to this computer using this username and password. Then the attack changes the binary version of the compiler, so that it checks if it is compiling the source code for the login program, and, if so, it reinserts the backdoor in the binary version. Thus, a system administrator cannot remove this Trojan horse simply by recompiling the login program. In fact, the attack goes a step further, so that the compiler also checks if it is compiling the source code of the C compiler itself, and, if so, it inserts the extra code that reinserts the backdoor for when it is compiling the login program. So recompiling the C compiler won't remove this attack either, and if anyone examines the source code for the login program or the compiler, they won't notice that anything is wrong. Now suppose your Unix system has been compromised in this way (which you confirm by logging in as 12345). How can you fix it, without using any outside resources (like a fresh copy of the operating system)? 02. Malware (10 points) In accepting the ACM Turing Award, Ken Thompson described a devious Trojan horse attack ona Une system, which most people now refer to as Thompson's rigged compiler. This attack changes the binary version of the login program to add a backdoor, say to allow a newnes, 12345, that has password, 67890, which is never checked against the password. Thus, the attacker can always login to this computer using this usemame and password. Then the attack changes the binary version of the compiler, so that it checks d it is coming the source code for the login program, and, if so, it reinserts the backdoor in the binary version. This system administrator cannot remove this Trojan horse simply by recompiling the log program na the attack goes a step further so that the compler also check it is compiling the source code of the compiler itself, and if so, it inserts the extra code that seinerts the backdoot for when st is compiling the login program. So recompiling the compiler won't remove this attack either, and if anyone examines the source code for the login program or the compiler, they won't notice that anything is wrong. Now suppose your une system has been comprised in this way (which you confirm by logging in as 123451. How can you fix it, without using any outside resources like a fresh copy of the operating systemi? 2.3 Encryption (40 points) Answer the following short questions 2. Caesar Cipher: Julius Caesar is about to invade Britain again and he send an encrypted message to one of his top commanders in the area that is now known as Cardiff Wales Unfortunately for fortunately depending on how you look at this messages intercepted by an intrepid band of Britons and they come to you asking for helpin decrypting the message. Here is the encrypted test: (15 points) DWWDFNDWGDZA Use your knowledge that this message was encrypted using a Casatopher with a shift of help these poor Britons decipher Caesar's message After deciphering the message the Britons decide to send back an impudent message to the despot Caesar. They ask you to encrypt the message GOBACITOROMEYOUIERK Using the same cipher that Caesar used what cipher test should be output to match this plaintext? b. What are the next three numbers in the pseudo-random number generator 3*2 mod 11 starting from 5? (5 points 4. Show the result of encrypting Musing the public keyle 3.77) in the SA cryptosystem (5 points) 22. Malware (10 points) In accepting the ACM Turing Award, Ken Thompson described a devious Trojan horse attack on a Unix system, which most people now refer to as Thompson's rigged compiler. This attack changes the binary version of the login program to add a backdoor, say, to allow a new user, 12345, that has password, 67890, which is never checked against the password. Thus, the attacker can always login to this computer using this username and password. Then the attack changes the binary version of the compiler, so that it checks if it is compiling the source code for the login program, and, if so, it reinserts the backdoor in the binary version. Thus, a system administrator cannot remove this Trojan horse simply by recompiling the login program. In fact, the attack goes a step further, so that the compiler also checks if it is compiling the source code of the C compiler itself, and, if so, it inserts the extra code that reinserts the backdoor for when it is compiling the login program. So recompiling the C compiler won't remove this attack either, and if anyone examines the source code for the login program or the compiler, they won't notice that anything is wrong. Now suppose your Unix system has been compromised in this way (which you confirm by logging in as 12345). How can you fix it, without using any outside resources (like a fresh copy of the operating system)