Modified Lab 1 IS

IS/Lab/Lab1/q1_monosub.py

@@ -1,6 +1,7 @@
 ## ptext = plaintext
+## ctext = ciphertext
+## mk = multiplicative key
 ## ak = additive key
-from collections import defaultdict
 
 def add_cipher_en(ptext, ak):
     result = ""
@@ -76,6 +77,10 @@ def affine_de(ctext, ak, mk):
             result += chr((((ord(ch) - 97 - ak) * inverse) % 26) + 97)
     return result
 
+def mult_inverse(mk):
+    inverse = pow(mk, -1, 26)
+    return inverse
+
 def operator(argument,ptext,ak,mk):
     match argument:
         case '1':
@@ -91,6 +96,7 @@ def operator(argument,ptext,ak,mk):
             print("Multiplicative Key: ", mk)
             ctext = mult_cipher_en(ptext, mk)
             print("Ciphertext: ", ctext)
+            print("Multiplicative Inverse: ", mult_inverse(mk))
             print("Decrypted Text: ", mult_cipher_de(ctext, mk))
         case '3':
             print("Affine Cipher")
@@ -99,6 +105,7 @@ def operator(argument,ptext,ak,mk):
             print("Multiplicative Key: ", mk)
             ctext = affine_en(ptext, ak, mk)
             print("Ciphertext: ", ctext)
+            print("Affine Inverse: ", mult_inverse(mk))
             print("Decrypted Text: ", affine_de(ctext, ak, mk))
         case '4':
             print("Goodbye")
@@ -122,6 +129,5 @@ def main():
         op = input("Enter your choice of operation: ")
         operator(op, ptext, ak, mk)
 
-
 if __name__ == '__main__':
     main()

IS/Lab/Lab1/q4_hill.py

@@ -1,18 +1,50 @@
-def hill_en(ptext,hk):
+import numpy as np
 
-def hill_de(ptext,hk):
+def hill_en(ptext, hk):
+    # all letters to uppercase
+    ptext = ''.join(c.upper() for c in ptext if c.isalpha())
+
+    # matrix size
+    n = int(len(hk)**0.5)
+
+    # key matrix
+    key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
+
+    # padding
+    ptext += 'X' * (-len(ptext) % n)
+
+    # block operation
+    result = ""
+    for i in range(0, len(ptext), n):
+        block = np.array([ord(c) - 65 for c in ptext[i:i+n]])
+        encrypted_block = (key @ block) % 26
+        result += ''.join(chr(val + 65) for val in encrypted_block)
+
+    return result
+
+def hill_de(ctext, hk):
+    # matrix size
+    n = int(len(hk)**0.5)
+
+    # key matrix and its inverse
+    key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
+    inv_key = np.linalg.inv(key).astype(int) % 26
+
+    # block operation
+    result = ""
+    for i in range(0, len(ctext), n):
+        block = np.array([ord(c) - 65 for c in ctext[i:i+n]])
+        decrypted_block = (inv_key @ block) % 26
+        result += ''.join(chr(val + 65) for val in decrypted_block)
+
+    return result
 
 def main():
-    ptext = input("Kindly enter your desired plaintext: ")
+    ptext = input("Plaintext: ")
-    hk = input("Kindly enter the Hill Key: ")
+    hk = input("Hill Key: ")
-
-    print("Welcome to the Hill cipher.")
-    print("Plaintext: ", ptext)
-    print("Hill Key: ", hk)
     ctext = hill_en(ptext, hk)
-    print("Ciphertext: ", ctext)
+    print(f"Ciphertext: {ctext}")
-    decrypted_text = hill_de(ctext, hk)
+    print(f"Decrypted: {hill_de(ctext, hk)}")
-    print("Decrypted Text: ", decrypted_text)
 
 if __name__ == '__main__':
-    main()
+    main()

IS/Lab/Lab1/q5_john.py

@@ -0,0 +1,21 @@
+def main():
+    shift = (ord('C') - ord('y')) % 26
+
+    ctext = "XVIEWYWI"
+    plaintext = ""
+
+    for char in ctext:
+        if char.isalpha():
+            shifted = ord(char.lower()) - shift
+            if shifted < ord('a'):
+                shifted += 26
+            plaintext += chr(shifted)
+        else:
+            plaintext += char
+
+    print(f"Attack type: Known plaintext attack")
+    print(f"Ciphertext: {ctext}")
+    print(f"Decrypted: {plaintext}")
+
+if __name__ == '__main__':
+    main()

IS/Lab/Lab1/q6_affine_bf.py

@@ -0,0 +1,47 @@
+def main():
+    # Affine cipher: E(x) = (ax + b) mod 26
+    # Given: "ab" -> "GL"
+    # a=0, b=1 -> G=6, L=11
+    # So: 6 = (a*0 + b) mod 26 -> b = 6
+    # And: 11 = (a*1 + b) mod 26 -> 11 = (a + 6) mod 26 -> a = 5
+
+    ciphertext = "XPALASXYFGFUKPXUSOGEUTKCDGEXANMGNVS"
+
+    # Try all possible values of a and b for affine cipher
+    for a in range(1, 26):
+        # a must be coprime to 26
+        if gcd(a, 26) != 1:
+            continue
+
+        for b in range(26):
+            # Check if this key produces "ab" -> "GL"
+            if (a * 0 + b) % 26 == 6 and (a * 1 + b) % 26 == 11:
+                # Found the key, now decrypt the message
+                a_inv = mod_inverse(a, 26)
+                decrypted = ""
+                for char in ciphertext:
+                    if char.isalpha():
+                        y = ord(char.upper()) - ord('A')
+                        x = (a_inv * (y - b)) % 26
+                        decrypted += chr(x + ord('A'))
+                    else:
+                        decrypted += char
+
+                print(f"Key found: a={a}, b={b}")
+                print(f"Ciphertext: {ciphertext}")
+                print(f"Decrypted: {decrypted}")
+                return
+
+def gcd(a, b):
+    while b:
+        a, b = b, a % b
+    return a
+
+def mod_inverse(a, m):
+    for i in range(1, m):
+        if (a * i) % m == 1:
+            return i
+    return None
+
+if __name__ == '__main__':
+    main()

OS/C/Week11/qq1.c

@@ -1,234 +1,11 @@
 #include <stdio.h>
 #include <stdlib.h>
-#include <limits.h>
+#include <math.h>
-
+#define MAX 100
-void sstf(int requests[], int n, int head) {
+void sstf(int a[],int n,int h){int v[MAX]={0},t=0,c=h;printf("\nSSTF:\n%d ",c);for(int i=0;i<n;i++){int x=-1,m=1e9;for(int j=0;j<n;j++){if(!v[j]){int d=abs(a[j]-c);if(d<m){m=d;x=j;}}}v[x]=1;t+=m;c=a[x];printf("->%d ",c);}printf("\nTotal:%d\n",t);}
-    int total_seek = 0;
+void sortAsc(int a[],int n){for(int i=0;i<n-1;i++)for(int j=i+1;j<n;j++)if(a[i]>a[j]){int t=a[i];a[i]=a[j];a[j]=t;}}
-    int completed = 0;
+void sortDesc(int a[],int n){for(int i=0;i<n-1;i++)for(int j=i+1;j<n;j++)if(a[i]<a[j]){int t=a[i];a[i]=a[j];a[j]=t;}}
-    int visited[100] = {0};
+void scan(int a[],int n,int h,int d){int l[MAX],r[MAX],x=0,y=0;for(int i=0;i<n;i++)if(a[i]<h)l[x++]=a[i];else r[y++]=a[i];sortDesc(l,x);sortAsc(r,y);int t=0,c=h;printf("\nSCAN:\n%d ",c);for(int i=0;i<x;i++){t+=abs(c-l[i]);c=l[i];printf("->%d ",c);}if(c){t+=c;c=0;printf("->%d ",c);}for(int i=0;i<y;i++){t+=abs(r[i]-c);c=r[i];printf("->%d ",c);}printf("\nTotal:%d\n",t);}
-    int current = head;
+void cscan(int a[],int n,int h,int d){int l[MAX],r[MAX],x=0,y=0;for(int i=0;i<n;i++)if(a[i]<h)l[x++]=a[i];else r[y++]=a[i];sortAsc(l,x);sortAsc(r,y);int t=0,c=h;printf("\nCSCAN:\n%d ",c);for(int i=0;i<y;i++){t+=abs(r[i]-c);c=r[i];printf("->%d ",c);}if(c!=d-1){t+=abs(d-1-c);c=d-1;printf("->%d ",c);}t+=d-1;c=0;printf("->%d ",c);for(int i=0;i<x;i++){t+=abs(l[i]-c);c=l[i];printf("->%d ",c);}printf("\nTotal:%d\n",t);}
-
+void clook(int a[],int n,int h){int l[MAX],r[MAX],x=0,y=0;for(int i=0;i<n;i++)if(a[i]<h)l[x++]=a[i];else r[y++]=a[i];sortAsc(l,x);sortAsc(r,y);int t=0,c=h;printf("\nCLOOK:\n%d ",c);for(int i=0;i<y;i++){t+=abs(r[i]-c);c=r[i];printf("->%d ",c);}if(x){t+=abs(c-l[0]);c=l[0];printf("->%d ",c);for(int i=1;i<x;i++){t+=abs(l[i]-c);c=l[i];printf("->%d ",c);}}printf("\nTotal:%d\n",t);}
-    printf("\nSSTF Disk Scheduling\n");
+int main(){int c,n,h,d,a[MAX];printf("1.SSTF\n2.SCAN\n3.CSCAN\n4.CLOOK\nChoice:");scanf("%d",&c);printf("Requests:");scanf("%d",&n);printf("Queue:");for(int i=0;i<n;i++)scanf("%d",&a[i]);printf("Head:");scanf("%d",&h);if(c==2||c==3){printf("Size:");scanf("%d",&d);}switch(c){case 1:sstf(a,n,h);break;case 2:scan(a,n,h,d);break;case 3:cscan(a,n,h,d);break;case 4:clook(a,n,h);break;default:printf("Invalid\n");}return 0;}
-    printf("Seek Sequence: %d", head);
-
-    while (completed < n) {
-        int min_distance = INT_MAX;
-        int min_index = -1;
-
-        for (int i = 0; i < n; i++) {
-            if (!visited[i]) {
-                int distance = abs(requests[i] - current);
-                if (distance < min_distance) {
-                    min_distance = distance;
-                    min_index = i;
-                }
-            }
-        }
-
-        visited[min_index] = 1;
-        current = requests[min_index];
-        total_seek += min_distance;
-        completed++;
-        printf(" -> %d", current);
-    }
-
-    printf("\nTotal Seek Time: %d\n", total_seek);
-}
-
-void scan(int requests[], int n, int head, int disk_size) {
-    int total_seek = 0;
-    int direction = 1; // 1 for moving right, 0 for moving left
-    int current = head;
-
-    printf("\nSCAN Disk Scheduling\n");
-    printf("Seek Sequence: %d", head);
-
-    // Sort requests
-    for (int i = 0; i < n; i++) {
-        for (int j = 0; j < n - i - 1; j++) {
-            if (requests[j] > requests[j + 1]) {
-                int temp = requests[j];
-                requests[j] = requests[j + 1];
-                requests[j + 1] = temp;
-            }
-        }
-    }
-
-    // Find position of head in sorted array
-    int index;
-    for (index = 0; index < n; index++) {
-        if (requests[index] >= head)
-            break;
-    }
-
-    // Move right
-    for (int i = index; i < n; i++) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    // Move to the end of disk
-    printf(" -> %d", disk_size - 1);
-    total_seek += abs(disk_size - 1 - head);
-    head = disk_size - 1;
-
-    // Move left
-    for (int i = index - 1; i >= 0; i--) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    printf("\nTotal Seek Time: %d\n", total_seek);
-}
-
-void cscan(int requests[], int n, int head, int disk_size) {
-    int total_seek = 0;
-    int current = head;
-
-    printf("\nC-SCAN Disk Scheduling\n");
-    printf("Seek Sequence: %d", head);
-
-    // Sort requests
-    for (int i = 0; i < n; i++) {
-        for (int j = 0; j < n - i - 1; j++) {
-            if (requests[j] > requests[j + 1]) {
-                int temp = requests[j];
-                requests[j] = requests[j + 1];
-                requests[j + 1] = temp;
-            }
-        }
-    }
-
-    // Find position of head in sorted array
-    int index;
-    for (index = 0; index < n; index++) {
-        if (requests[index] >= head)
-            break;
-    }
-
-    // Move right
-    for (int i = index; i < n; i++) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    // Move to the end of disk
-    printf(" -> %d", disk_size - 1);
-    total_seek += abs(disk_size - 1 - head);
-
-    // Move to the beginning
-    printf(" -> 0");
-    total_seek += disk_size - 1;
-    head = 0;
-
-    // Move right again
-    for (int i = 0; i < index; i++) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    printf("\nTotal Seek Time: %d\n", total_seek);
-}
-
-void clook(int requests[], int n, int head) {
-    int total_seek = 0;
-    int current = head;
-
-    printf("\nC-LOOK Disk Scheduling\n");
-    printf("Seek Sequence: %d", head);
-
-    // Sort requests
-    for (int i = 0; i < n; i++) {
-        for (int j = 0; j < n - i - 1; j++) {
-            if (requests[j] > requests[j + 1]) {
-                int temp = requests[j];
-                requests[j] = requests[j + 1];
-                requests[j + 1] = temp;
-            }
-        }
-    }
-
-    // Find position of head in sorted array
-    int index;
-    for (index = 0; index < n; index++) {
-        if (requests[index] >= head)
-            break;
-    }
-
-    // Move right
-    for (int i = index; i < n; i++) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    // Move to first request
-    for (int i = 0; i < index; i++) {
-        current = requests[i];
-        printf(" -> %d", current);
-        total_seek += abs(current - head);
-        head = current;
-    }
-
-    printf("\nTotal Seek Time: %d\n", total_seek);
-}
-
-int main() {
-    int requests[100], n, head, disk_size, choice;
-
-    printf("Enter the number of disk requests: ");
-    scanf("%d", &n);
-
-    printf("Enter the disk requests: ");
-    for (int i = 0; i < n; i++) {
-        scanf("%d", &requests[i]);
-    }
-
-    printf("Enter the initial head position: ");
-    scanf("%d", &head);
-
-    printf("Enter the disk size (0 to size-1): ");
-    scanf("%d", &disk_size);
-
-    do {
-        printf("\n\nDisk Scheduling Algorithms\n");
-        printf("1. SSTF (Shortest Seek Time First)\n");
-        printf("2. SCAN\n");
-        printf("3. C-SCAN\n");
-        printf("4. C-LOOK\n");
-        printf("5. Exit\n");
-        printf("Enter your choice: ");
-        scanf("%d", &choice);
-
-        switch (choice) {
-            case 1:
-                sstf(requests, n, head);
-                break;
-            case 2:
-                scan(requests, n, head, disk_size);
-                break;
-            case 3:
-                cscan(requests, n, head, disk_size);
-                break;
-            case 4:
-                clook(requests, n, head);
-                break;
-            case 5:
-                printf("Exiting program...\n");
-                break;
-            default:
-                printf("Invalid choice!\n");
-        }
-    } while (choice != 5);
-
-    return 0;
-}

OS/C/Week12/rtos.c

@@ -1,153 +1,52 @@
 #include <stdio.h>
-
-// Define Task structure (simplified for memorization)
 typedef struct {
-    int id;                 // Task ID
+    int id,p,et,re,ad,ta;
-    int period;             // Period (also deadline for simplicity)
-    int execution_time;     // Worst-case execution time (WCET)
-    // --- Simulation State ---
-    int remaining_execution; // Remaining execution time for current instance
-    int absolute_deadline;   // Absolute deadline for current instance
-    int time_to_arrival;     // Time until the next instance arrives/is released
 } Task;
 
-// --- Global Variables ---
+Task tasks[]={{1,5,2,0,0,0},{2,8,3,0,0,0}};
-// Define the tasks for the simulation (Example Set)
+int nt=sizeof(tasks)/sizeof(Task);
-// Format: {id, Period, ExecutionTime, 0, 0, 0} <-- Initial state values
+int st=40;
-Task tasks[] = {
-    {1, 5, 2, 0, 0, 0},  // Task 1: Period=5, Exec Time=2
-    {2, 8, 3, 0, 0, 0}   // Task 2: Period=8, Exec Time=3
-    // Add more tasks here if needed
-};
-// Calculate number of tasks automatically
-int num_tasks = sizeof(tasks) / sizeof(Task);
-// Set simulation duration (e.g., Hyperperiod or a fixed time)
-// LCM(5, 8) = 40
-int simulation_time = 40;
 
-// --- Rate Monotonic (RM) Simulation ---
+void simulate_rm(){
-void simulate_rm() {
+    printf("--- RM ---\n");
-    printf("--- Rate Monotonic Scheduling ---\n");
+    for(int i=0;i<nt;i++){tasks[i].re=tasks[i].ad=tasks[i].ta=0;}
-    // Reset task states for the simulation run
+    for(int t=0;t<st;t++){
-    for (int i = 0; i < num_tasks; i++) {
+        for(int i=0;i<nt;i++){
-        tasks[i].remaining_execution = 0;
+            if(!tasks[i].ta){
-        tasks[i].absolute_deadline = 0;
+                if(tasks[i].re>0)printf("!T%d:Task%d missed!\n",t,tasks[i].id);
-        tasks[i].time_to_arrival = 0; // All tasks start at time 0
+                tasks[i].re=tasks[i].et;
-    }
+                tasks[i].ad=t+tasks[i].p;
-
+                tasks[i].ta=tasks[i].p;
-    // Main simulation loop
-    for (int time = 0; time < simulation_time; time++) {
-        // 1. Check for task arrivals (release time)
-        for (int i = 0; i < num_tasks; i++) {
-            if (tasks[i].time_to_arrival == 0) {
-                // Check if the previous instance of this task missed its deadline
-                if (tasks[i].remaining_execution > 0) {
-                    printf("!!! Time %d: Task %d MISSED DEADLINE !!!\n", time, tasks[i].id);
-                    // Simple handling: Continue with the new instance, old one is lost
-                }
-                // Release new instance of the task
-                tasks[i].remaining_execution = tasks[i].execution_time;
-                tasks[i].absolute_deadline = time + tasks[i].period; // Deadline = Period
-                tasks[i].time_to_arrival = tasks[i].period; // Set timer for the *next* arrival
             }
-            tasks[i].time_to_arrival--; // Decrement time until the next arrival for all tasks
+            tasks[i].ta--;
-        }
-
-        // 2. Select highest priority task to run (RM: Shortest Period has highest priority)
-        int task_to_run = -1; // -1 indicates CPU Idle
-        int highest_priority = 10000; // Initialize with a low priority (large period)
-
-        for (int i = 0; i < num_tasks; i++) {
-            // Check if task is ready (has arrived and needs execution)
-            if (tasks[i].remaining_execution > 0) {
-                // RM priority check: Lower period value means higher priority
-                if (tasks[i].period < highest_priority) {
-                    highest_priority = tasks[i].period;
-                    task_to_run = i; // Select this task
-                }
-            }
-        }
-
-        // 3. Execute the selected task (or remain idle)
-        if (task_to_run != -1) {
-            // Task selected to run
-            printf("Time %d: Task %d running\n", time, tasks[task_to_run].id);
-            tasks[task_to_run].remaining_execution--; // Execute for one time unit
-
-            // Optional: Check if task just finished
-            // if (tasks[task_to_run].remaining_execution == 0) {
-            //     printf("Time %d: Task %d finished\n", time + 1, tasks[task_to_run].id);
-            // }
-        } else {
-            // No task ready to run
-            printf("Time %d: CPU Idle\n", time);
         }
+        int r=-1,hp=10000;
+        for(int i=0;i<nt;i++)
+            if(tasks[i].re>0&&tasks[i].p<hp){hp=tasks[i].p;r=i;}
+        if(r>=0){printf("T%d:Task%d run\n",t,tasks[r].id);tasks[r].re--;}
+        else printf("T%d:Idle\n",t);
     }
-    printf("--- RM Simulation Complete ---\n");
 }
 
-// --- Earliest Deadline First (EDF) Simulation ---
+void simulate_edf(){
-void simulate_edf() {
+    printf("\n--- EDF ---\n");
-    printf("\n--- Earliest Deadline First Scheduling ---\n");
+    for(int i=0;i<nt;i++){tasks[i].re=tasks[i].ad=tasks[i].ta=0;}
-    // Reset task states
+    for(int t=0;t<st;t++){
-    for (int i = 0; i < num_tasks; i++) {
+        for(int i=0;i<nt;i++){
-        tasks[i].remaining_execution = 0;
+            if(!tasks[i].ta){
-        tasks[i].absolute_deadline = 0;
+                if(tasks[i].re>0)printf("!T%d:Task%d missed!\n",t,tasks[i].id);
-        tasks[i].time_to_arrival = 0;
+                tasks[i].re=tasks[i].et;
-    }
+                tasks[i].ad=t+tasks[i].p;
-
+                tasks[i].ta=tasks[i].p;
-    // Main simulation loop
-    for (int time = 0; time < simulation_time; time++) {
-        // 1. Check for task arrivals (same as RM)
-        for (int i = 0; i < num_tasks; i++) {
-            if (tasks[i].time_to_arrival == 0) {
-                if (tasks[i].remaining_execution > 0) {
-                    printf("!!! Time %d: Task %d MISSED DEADLINE !!!\n", time, tasks[i].id);
-                }
-                tasks[i].remaining_execution = tasks[i].execution_time;
-                tasks[i].absolute_deadline = time + tasks[i].period;
-                tasks[i].time_to_arrival = tasks[i].period;
             }
-            tasks[i].time_to_arrival--;
+            tasks[i].ta--;
-        }
-
-        // 2. Select highest priority task to run (EDF: Earliest Absolute Deadline has highest priority)
-        int task_to_run = -1;
-        int earliest_deadline = 10000; // Initialize with a late deadline
-
-        for (int i = 0; i < num_tasks; i++) {
-            // Check if task is ready
-            if (tasks[i].remaining_execution > 0) {
-                // EDF priority check: Lower deadline value means higher priority (earlier deadline)
-                if (tasks[i].absolute_deadline < earliest_deadline) {
-                    earliest_deadline = tasks[i].absolute_deadline;
-                    task_to_run = i; // Select this task
-                }
-            }
-        }
-
-        // 3. Execute the selected task (same as RM)
-        if (task_to_run != -1) {
-            printf("Time %d: Task %d running\n", time, tasks[task_to_run].id);
-            tasks[task_to_run].remaining_execution--;
-            // Optional: Check finish
-            // if (tasks[task_to_run].remaining_execution == 0) {
-            //     printf("Time %d: Task %d finished\n", time + 1, tasks[task_to_run].id);
-            // }
-        } else {
-            printf("Time %d: CPU Idle\n", time);
         }
+        int r=-1,ed=10000;
+        for(int i=0;i<nt;i++)
+            if(tasks[i].re>0&&tasks[i].ad<ed){ed=tasks[i].ad;r=i;}
+        if(r>=0){printf("T%d:Task%d run\n",t,tasks[r].id);tasks[r].re--;}
+        else printf("T%d:Idle\n",t);
     }
-    printf("--- EDF Simulation Complete ---\n");
 }
 
-// --- Main Function ---
+int main(){simulate_rm();simulate_edf();return 0;}
-int main() {
-    // Run Rate Monotonic simulation
-    simulate_rm();
-
-    // Run Earliest Deadline First simulation
-    simulate_edf();
-
-    return 0; // Indicate successful execution
-}