finished task 4.

hw3/task4/.gitignore

@@ -0,0 +1,2 @@
+find_key
+testing.txt

hw3/task4/find_key.cpp

@@ -1,12 +1,15 @@
 #include <cstdio>
 #include <iostream>
 #include <fstream>
+#include <sstream>
 #include <cstring>
 #include <ctype.h>
 #include <openssl/evp.h>
 
 using namespace std;
 
+// This is the same as what was given, just added the key string as a parameter
+// so I could manipulate it in here instead.
 int do_crypt(FILE *in, FILE *out, string inkey, int do_encrypt)
 {
     /* Allow enough space in output buffer for additional block */
@@ -17,23 +20,20 @@ int do_crypt(FILE *in, FILE *out, string inkey, int do_encrypt)
      * Bogus key and IV: we'd normally set these from
      * another source.
     */
-    unsigned char iv[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
-    //unsigned char iv[] = "0000000000000000";
-    unsigned char key[16];
     
-    for(int i = 0; i < 16; i++)
+    // hardcoding the IV because we already know what it is.
+    unsigned char iv[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
+    
+    // I'm adding the spaces in here.
+    for(int i = inkey.length(); i < 16; ++i)
     {
-        if(i < inkey.length())
-        {
-            key[i] = inkey.at(i);
+        inkey += ' ';
     }
-        else
-        {
-            key[i] = '\x20';
-        }
-    }
-    //string str( key, key + sizeof key / sizeof key[0] );
-    //cout << str << endl;
+
+    // Converting the input key into an unsigned char array.
+    unsigned char key[17];
+    strcpy((char*) key, inkey.c_str());
+    
     /* Don't set key or IV right away; we want to check lengths */
     ctx = EVP_CIPHER_CTX_new();
     EVP_CipherInit_ex(ctx, EVP_aes_128_cbc(), NULL, NULL, NULL, do_encrypt);
@@ -42,7 +42,7 @@ int do_crypt(FILE *in, FILE *out, string inkey, int do_encrypt)
     /* Now we can set key and IV */
     EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt);
     for (;;) {
-        inlen = fread(inbuf, 1, 256, in);
+        inlen = fread(inbuf, 1, 1024, in);
         if (inlen <= 0)
             break;
         if (!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf, inlen)) {
@@ -55,75 +55,95 @@ int do_crypt(FILE *in, FILE *out, string inkey, int do_encrypt)
     if (!EVP_CipherFinal_ex(ctx, outbuf, &outlen)) {
         /* Error */
         EVP_CIPHER_CTX_free(ctx);
+
+        // I added this just in case to make sure thigns cleaned up properly.
+        EVP_CIPHER_CTX_cleanup(ctx);
         return 0;
     }
 
-    cout << "I made it." << endl;
-    if(outlen > 0)
-        cout << outbuf << endl;
     fwrite(outbuf, 1, outlen, out);
 
     EVP_CIPHER_CTX_free(ctx);
+    EVP_CIPHER_CTX_cleanup(ctx);
     return 1;
 }
 
 int main()
 {
-    cout << "Test." << endl;
-
+    // Initialize files.
     FILE *input;
     FILE *output;
-    //FILE *original;
 
+    // Open the needed files.
     input = fopen("ciphertext.txt", "rb");
     output = fopen("testing.txt", "wb");
-    //original = fopen("plaintext.txt", "r");
 
+    // I prefer ifstreams when dealing with files,
+    // but I leave the other two as file pointers
+    // so I don't have to change more code.
     ifstream words("words.txt");
     ifstream original("plaintext.txt");
 
+    // Just an initial key. It will be overwritten.
     string key = "0123456789abcdef";
     
+    // Variable to storing the goal string.
     string secret = "";
     getline(original, secret);
 
-    char line[256];
-
-    unsigned char keyc[16];
+    // Variable for storing output when we read
+    // from the file that we wrote to.
+    string templine = "";
 
     while(!words.eof())
     {
+        // Get the current key to test with.
         key = "";
         getline(words, key);
+
+        // Only test it if it's less that 16 characters.
         if(key.length() > 16)
         {
             continue;
         }
-        //cout << key << endl;
 
+        // Try to decrypt with this key.
         do_crypt(input, output, key, 0);
 
+        // Set the file pointers back to the beginning
+        // of the files.
+        rewind(input);
+        rewind(output);
+
+        // Read the file and see if it matches the original
+        // message, if it does, then we guessed the key.
         fclose(output);
-        output = fopen("testing.txt", "r");
         
-        if (NULL != output)
+        ifstream tempoutput("testing.txt");
+
+        getline(tempoutput, templine);
+
+        tempoutput.close();
+
+        if(templine.compare("This is a top secret.") == 0)
         {
-            fseek (output, 0, SEEK_END);
-            int size = ftell(output);
-            
-            if (0 != size)
+            // Output the key and the output text
+            // to prove we know the key and we
+            // successfully decrypted the message.
+            cout << key << endl;
+            cout << templine << endl;
+            break;
+        }
+        else
         {
-                fgets(line, sizeof(line), output);
-                cout << key << "\t" << secret << "\t" << line << endl;
-            }
-        }
-
-        fclose(output);
+            // We didn't decrypt it, try again,
+            // overwrite whatever was in the file.
             output = fopen("testing.txt", "wb");
         }
 
+    }
+
     fclose(input);
-    fclose(output);
     words.close();
     original.close();
 

hw3/task4/find_key.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+filename="itworkmaybe.txt"
+while read line; do
+    openssl enc -aes-128-cbc -d -in ciphertext.txt -out itworkmaybe.txt -iv 0000000000000000 -K $line
+    read aline < "$filename"
+    if [ "$aline" == "This is a top secret." ]; then
+        echo $line
+        break
+    fi
+done < "$1"