Choose a prefix for the password recovery

include/Arguments.hpp

@@ -58,6 +58,7 @@ class Arguments
 
         std::size_t maxLength = 0; ///< Maximum password length to try during password recovery
         bytevec charset; ///< Characters to generate password candidates
+        std::string prefix; ///< Expected recovered password prefix
 
         bool help = false; ///< Tell whether help message is needed or not
 

include/password.hpp

@@ -14,7 +14,7 @@ class Recovery
         Recovery(const Keys& keys, const bytevec& charset, Progress& progress);
 
         /// Look for a password of length 6 or less
-        bool recoverShortPassword();
+        bool recoverShortPassword(const Keys& initial);
 
         /// Look for a password of given length (at least 7)
         bool recoverLongPassword(const Keys& initial, std::size_t length);
@@ -43,6 +43,6 @@ class Recovery
 };
 
 /// Try to recover the password associated with the given keys
-bool recoverPassword(const Keys& keys, std::size_t max_length, const bytevec& charset, std::string& password, Progress& progress);
+bool recoverPassword(const std::string& prefix, const Keys& keys, std::size_t max_length, const bytevec& charset, std::string& password, Progress& progress);
 
 #endif // BKCRACK_PASSWORD_HPP

src/Arguments.cpp

@@ -140,6 +140,9 @@ void Arguments::parseArgument()
             maxLength = readSize("length");
             charset = readCharset();
             break;
+        case 'm':
+            prefix = readString("prefix");
+            break;
         case 'h':
             help = true;
             break;

src/main.cpp

@@ -51,6 +51,7 @@ Crack legacy zip encryption with Biham and Kocher's known plaintext attack.
                       ?a alpha-numerical characters (same as ?l?u?d)
                       ?p printable characters (same as ?a?s)
                       ?b all bytes (0x00 - 0xff)
+ -m prefix          The expected starting characters of the password to recover
 
  -h                 Show this help and exit)_";
 
@@ -168,7 +169,7 @@ try
 
         {
             ConsoleProgress progress(std::cout);
-            success = recoverPassword(keysvec.front(), args.maxLength, args.charset, password, progress);
+            success = recoverPassword(args.prefix, keysvec.front(), args.maxLength, args.charset, password, progress);
         }
 
         if(success)

src/password.cpp

@@ -38,19 +38,19 @@ Recovery::Recovery(const Keys& keys, const bytevec& charset, Progress& progress)
     }
 }
 
-bool Recovery::recoverShortPassword()
+bool Recovery::recoverShortPassword(const Keys& initial)
 {
-    Keys initial;
+    Keys init = initial;
 
     for(int length = 6; length >= 0; length--)
     {
-        if(recover(initial))
+        if(recover(init))
         {
             password.erase(0, 6 - length);
             return true;
         }
 
-        initial.updateBackwardPlaintext(charset.front());
+        init.updateBackwardPlaintext(charset.front());
     }
 
     return false;
@@ -176,16 +176,17 @@ bool Recovery::recursion(int i)
     return false;
 }
 
-bool recoverPassword(const Keys& keys, std::size_t max_length, const bytevec& charset, std::string& password, Progress& progress)
+bool recoverPassword(const std::string& prefix, const Keys& keys, std::size_t max_length, const bytevec& charset, std::string& password, Progress& progress)
 {
     Recovery worker(keys, charset, progress);
+    const Keys initial{prefix};
 
     // look for a password of length between 0 and 6
     progress.log([](std::ostream& os) { os << "length 0-6..." << std::endl; });
 
-    if(worker.recoverShortPassword())
+    if(worker.recoverShortPassword(initial))
     {
-        password = worker.getPassword();
+        password = prefix + worker.getPassword();
         progress.state = Progress::State::EarlyExit;
         return true;
     }
@@ -195,9 +196,9 @@ bool recoverPassword(const Keys& keys, std::size_t max_length, const bytevec& ch
     {
         progress.log([length](std::ostream& os) { os << "length " << length << "..." << std::endl; });
 
-        if(worker.recoverLongPassword(Keys{}, length))
+        if(worker.recoverLongPassword(initial, length))
         {
-            password = worker.getPassword();
+            password = prefix + worker.getPassword();
             progress.state = Progress::State::EarlyExit;
             return true;
         }
@@ -222,15 +223,13 @@ bool recoverPassword(const Keys& keys, std::size_t max_length, const bytevec& ch
             if(progress.state != Progress::State::Normal)
                 continue; // cannot break out of an OpenMP for loop
 
-            Keys init;
+            Keys init = initial;
             init.update(charset[i / charsetSize]);
             init.update(charset[i % charsetSize]);
 
             if(worker.recoverLongPassword(init, length - 2))
             {
-                password = worker.getPassword();
-                password.insert(password.begin(), charset[i % charsetSize]);
-                password.insert(password.begin(), charset[i / charsetSize]);
+                password = prefix + static_cast<char>(charset[i / charsetSize]) + static_cast<char>(charset[i % charsetSize]) + worker.getPassword();
                 found = true;
                 progress.state = Progress::State::EarlyExit;
             }