Properly implement calibration

barf.py

@@ -41,7 +41,7 @@ def main():
     bm = BreakpointManager(args["positiveAddr"], args["negativeAddr"], args["winAddr"])
 
     # Manage the target with the TargetManager
-    tm = TargetManager(args["persistent"], args["startAddr"], args["endAddr"], args["buffAddr"])
+    tm = TargetManager(bm, args["persistent"], args["startAddr"], args["endAddr"], args["buffAddr"])
 
     # start the bruteforcing madness ;)
     Bruteforce(bm, tm, args["knownPrefix"], args["knownSuffix"], args["chunksize"])

src/Bruteforce.py

@@ -14,14 +14,10 @@ def BruteforceChar(bm, tm, knownPrefix, knownSuffix, chunksize):
 
     found = False
 
-    ## detect best score
-    # we want to get the score for "everything correct except last character".
-    # we do this by combining knownPrefix + keyFragment with an "impossible" character.
-    # the resulting score is the base for the next round of guessing, hopefully with a single solution better than the score of knownPrefix + keyFragment + impossibleChar.
-    # please also note that this will massively fail if the "impossible" character is part of the flag, at the very position it was tested on ... have fun detecting that
-    bm.ResetBreakpoints()
-    tm.Run(knownPrefix + keyFragment + "^" * chunksize + knownSuffix)
-    refScore = bm.PopScore()
+    # detect best score
+    refScore = Calibrate(bm, tm, knownPrefix + keyFragment, knownSuffix, chunksize)
+    if refScore is False:
+        return False
 
     # iterate over every character in the charset
     for c in generateCharset(chunksize):
@@ -29,9 +25,7 @@ def BruteforceChar(bm, tm, knownPrefix, knownSuffix, chunksize):
         inp = knownPrefix + keyFragment + c + knownSuffix
 
         # and try it
-        bm.ResetBreakpoints()
-        tm.Run(inp)
-        score = bm.PopScore()
+        score = RunAndScore(bm, tm, inp)
         
         # yay, that's a hit
         if score > refScore or bm.HitWin():
@@ -79,6 +73,38 @@ def Bruteforce(bm, tm, knownPrefix, knownSuffix, chunksize):
                 return knownPrefix + knownSuffix
 
 
+# Finds out the base score when filling the binary with partly correct chars (e.g. the already found-to-be-correct prefix)
+# It does this by combining knownPrefix + keyFragment and knownSuffix with an "impossible" character.
+# We're only able to proceed if every character (except one) returns the same score - the "except one" score is the winner ;)
+# Note that this function will massively fail if the "impossible" character is part of the flag, at the very position it was tested on ... have fun detecting that
+def Calibrate(bm, tm, prefix, suffix, chunksize):
+    score1 = RunAndScore(bm, tm, prefix + '^' * chunksize + suffix)
+    score2 = RunAndScore(bm, tm, prefix + '`' * chunksize + suffix)
+
+    if score1 == score2:
+        # we found a stable score, return it
+        return score1
+    else:
+        # There is some kind of inconsistency in the executable, stop here.
+        EnableLogging()
+        print(score1)
+        print(score2)
+        print("BARF was unable to calibrate.")
+        print("While this may have multiple reasons, the most realistic are:")
+        print(" - The specified binary is not solvable on a round-based approach")
+        print("   -> reverse the binary further - is there some shuffeling mechanism in place?")
+        print(" - The 'no way that character is part of the flag' charset is actually part of the flag")
+        DisableLogging()
+        return False
+
+
+# Runs the given input and returns its breakpoint score
+def RunAndScore(bm, tm, inp):
+    bm.ResetBreakpoints()
+    tm.Run(inp)
+    return bm.PopScore()
+
+
 # generateCharset returns an iteratable object (string or set) to be used by the bruteforce function.
 # the chunksize is the amount of characters to stuff into an entry
 def generateCharset(chunksize):

src/TargetManager.py

@@ -13,6 +13,7 @@ from PersistenceBreakpoint import PersistenceBreakpoint
 # The TargetManager aims to be the one-size-fits-all solution for execution handling.
 # That means it is designed to have a unified interface, independent of e.g. persistent mode.
 class TargetManager:
+    breakpointManager = None
     usePersistent = False
 
     # vars used for persistent mode
@@ -22,11 +23,13 @@ class TargetManager:
     checkpointIndex = 1
     isRunning = False
 
+    # bm is the BreakpointManager in use
     # usePersistent is a boolean, determing if the experimental persistent mode should be used
     # startAddr is the address to start the persistent run
     # endAddr is the address to jump back to startAddr
     # buffAddr is the address of the target buffer to be written in persistent mode
-    def __init__(self, usePersistent, startAddr, endAddr, buffAddr):
+    def __init__(self, bm, usePersistent, startAddr, endAddr, buffAddr):
+        self.breakpointManager = bm
         self.usePersistent = usePersistent
         
         if usePersistent:
@@ -68,6 +71,9 @@ class TargetManager:
                 # Please note, as this may cast some confusion, that at this point the binary
                 # had a full run-thru, is equipped with checkpoints and breakpoints and is
                 # currently in break mode (not running, so to speak), and is at startAddr.
+                # But, because we likely already hit some breakpoints (depends on the executable),
+                # we need to reset the scores.
+                self.breakpointManager.ResetBreakpoints()
  
             # the executable is already running and reset
             # means we just need to feed input into the binary, then continue running it