Merge branch 'master' of gitlab.com:shockrah/csnotes

312/hw/2/2.md

@@ -0,0 +1,59 @@
+---
+title: Homework 2
+author: Alejandro Santillana
+---
+
+
+# Section 1 - Symmetric Key Cryptography
+
+1. The two approaches to attacking a given cipher are using _brute force_ or _cryptanalysis_. Brute force methods are a simpler method of attack because they naively try all possible inputs for a given output. Cryptanalysis is the process of using the particular characteristics of a cipher to de-cipher the original message.
+
+2. Chosen plain text attacks involve using a given plain text to determine a cipher text. The attacker themselves choose the plain text and have some kind of cipher text available to them. The algorithm on the other hand is not known to the attacker when performing cryptanalysis. In this way a black box approach to reversing the cipher is taken.
+
+3. Cryptography is the study and practice of creating hidden messages from plain messages. Cryptanalysis is the practice of analyzing hidden messages to determine a plain message.
+
+4. Unconditionally secure ciphers are ciphers which are considered secure regardless of how many resources or time are given to reversing the cipher, sometimes due to not having enough information to determine anything useful. Computationally secure ciphers exist on the premise that it is impractical to attempt to break the cipher given a limited amount of compute power.
+
+5. Key distribution is the first major hurdle to ensure that the one time pad is used effectively. Without properly secure channels to share the key the scheme of a one time pad can not be trusted. The other issue is that the key must be longer than the message itself in order to ensure that parts of it are never reused.
+
+# Section 2
+
+1.  Encode: _This is an easy problem_. \
+Decode: _rmij'u uamu xyj_. \
+Plaintext letter:  a b c d e f g h i j k l m n o p q r s t u v w x y z  \
+Ciphertext letter: m n b v c x z a s d f g h j k l p o i u y t r e w q \
+```
+Encode portion: uasi si mncmiw lokngch
+Decode portion: wasn't that fun
+```
+
+
+
+2. Plain Text: _Must see you over Cadogan West. Coming at once._ \
+Key: _largest_
+```
+Part A:
+
+L A R G E 
+S T B C D 
+F H I K M
+N O P Q U
+V W X Y Z
+Encoded: UZTB DLG ZPN NWLG TGTUERO VLDB DUHFPE RH WQSRZ
+
+Part B: 
+Encoded: UZTB DLG ZPN NWLG TGTUERO VLDB DUHFPE RH WQSRZ
+
+```
+
+3. Message: "_Let's skip class and go to the beach_" \
+Depth = 4 \
+```
+L   S   C   S   G   T   E                                   
+ E   K   L   A   O   H   A                                  
+  T   I   A   N   T   E   C                                 
+   S   P   S   D   O   B   H                               
+Message: LSCSGTEEKLAOHATIANTECSPSDOBH
+```
+
+

334/.gitignore

@@ -0,0 +1,4 @@
+bin
+msh
+*txt
+*sh

334/Makefile

@@ -1,10 +1,16 @@
 # Single make file for everything becauz lazy
-object=hw.c
+object=homework/msh/msh.c
 cc=gcc
-output=bin
+output=msh
+tmps=*txt
 
 default:
 	$(cc) $(object) -o $(output)
 
+run:
+	./bin
+
+
 clean:
 	rm -f $(output)
+	rm -f $(tmps)

334/homework/2/msh.c

@@ -1,46 +0,0 @@
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-#define PROMPT "msh> "
-#define EXIT_CMD "exit"
-#define MAX_BUF 121
-
-void echo(const char*);
-void remove_newline(char*);
-void exit_branch(const char*);
-
-int main(void) {
-	char buffer[MAX_BUF];
-	while(1) {
-		printf("%s", PROMPT);
-		fgets(buffer, MAX_BUF, stdin);
-		if(!strlen(buffer)) {
-			return 0;
-		}
-		// process the input
-		remove_newline(buffer);
-		exit_branch(buffer);
-		echo(buffer);
-	}
-	return 0;
-}
-
-void echo(const char* buf) {
-	printf("%s\n", buf);
-}
-
-
-void remove_newline(char* buf) {
-	char* c = buf;
-	while(*c != '\n') { c++; }
-	*c='\0';
-}
-
-void exit_branch(const char* buf) {
-	if(strcmp(buf, EXIT_CMD)) {
-		return;
-	}
-	exit(0);
-	return; // just for gcc but exit shouldn't fail
-}

334/homework/msh/msh.c

@@ -15,18 +15,36 @@
 #define RESP_DATE 2
 #define RESP_ECHO 3
 #define RESP_SHELL 4
+#define RESP_CD_FAIL -1
+#define RESP_CD_SUCCESS 6
+
+// Sub statuses that are generally nice to have
+#define CD_NOP 0x1
 
 void echo(const char*);
 void remove_newline(char*);
 void exit_branch(const char*);
 int  builtin_response(char*);
+int cd_handler(char**, const int);
 
-
-int main(void) {
+int main(int argc, char** argv) {
+	FILE* file = NULL;
+	if(argc == 2) {
+		file = fopen(argv[1], "r");
+		if(!file) { return 1; }
+	}
 	char buffer[MAX_BUF];
 	while(1) {
-		printf("%s", PROMPT);
-		fgets(buffer, MAX_BUF, stdin);
+		// determine if we're reading from stdin or a stream of some sort
+		if(file == NULL && isatty(STDIN_FILENO)) {
+			printf("%s", PROMPT);
+			fgets(buffer, MAX_BUF, stdin);
+		}
+		else {
+			fgets(buffer, MAX_BUF, file);
+			printf("buffer: %s\n", buffer);
+		}
+
 		// Deal with EOF input
 		if(!strlen(buffer)) {
 			exit(0);
@@ -41,6 +59,8 @@ int main(void) {
 				echo(buffer);
 			case RESP_SHELL: // shell command handler was used
 				continue;
+			case RESP_CD_FAIL:
+				printf("msh: cd: No such file or directory\n");
 		}
 		memset(buffer, 0x00, MAX_BUF); // reset buffer after each usage
 	}
@@ -82,6 +102,9 @@ int builtin_response(char* buffer) {
 		return RESP_DATE;
 	}
 
+
+
+	// Populate tokens
 	char *tokens[64];
 	int idx = 0;
 	for(char* cur = strtok(buffer, STRING_DELIMITER); cur != NULL; cur=strtok(NULL, STRING_DELIMITER)) { 
@@ -92,6 +115,12 @@ int builtin_response(char* buffer) {
 		idx++;
 	}
 
+	// Handling director changes
+	int cd_result = cd_handler(tokens, idx);
+	if(cd_result != CD_NOP) {
+		return cd_result;
+	}
+
 	// Execute child process
 	pid_t child = fork();
 	if(child != 0) {
@@ -109,3 +138,14 @@ int builtin_response(char* buffer) {
 	}
 
 }
+
+int cd_handler(char** tokens, const int t_count) {
+	if(!strcmp(tokens[0], "cd")) {
+		if(t_count < 2) {
+			int ret = chdir(getenv("HOME"));
+			return ret;
+		}
+		return chdir(tokens[1]);
+	}
+	return CD_NOP;
+}