Fixing checksum uri generator again.

This time, it's ensured that generate_uri_checksum(sum) will succeed,
provided the sum is an even number between 80 and 100 (tested)

It's still not great for arbitrary checksum targets, but that's because
there are lots of strings that cannot satisfy the requirement. I kind of
think this is the fault of Rex.

lib/msf/core/handler/reverse_http.rb

@@ -60,14 +60,17 @@ module ReverseHttp
 		
 		uri_match
 	end
-	
+
 	#
 	# Create a URI that matches a given checksum
 	#
 	def generate_uri_checksum(sum)
-		uri = Rex::Text.rand_text_alphanumeric(3)
-		("a".."z").sort_by {rand}.each do |x|
-			return(uri + x) if Rex::Text.checksum8(uri + x)
+		chk = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a
+		32.times do 
+			uri = Rex::Text.rand_text_alphanumeric(3)
+			chk.sort_by {rand}.each do |x|
+				return(uri + x) if Rex::Text.checksum8(uri + x) == sum
+			end
 		end
 		raise RuntimeError, "Unable to generate a string with checksum #{sum}"
 	end

lib/msf/core/handler/reverse_https.rb

@@ -66,9 +66,12 @@ module ReverseHttps
 	# Create a URI that matches a given checksum
 	#
 	def generate_uri_checksum(sum)
-		uri = Rex::Text.rand_text_alphanumeric(3)
-		("a".."z").sort_by {rand}.each do |x|
-			return(uri + x) if Rex::Text.checksum8(uri + x)
+		chk = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a
+		32.times do 
+			uri = Rex::Text.rand_text_alphanumeric(3)
+			chk.sort_by {rand}.each do |x|
+				return(uri + x) if Rex::Text.checksum8(uri + x) == sum
+			end
 		end
 		raise RuntimeError, "Unable to generate a string with checksum #{sum}"
 	end