From 4ed371cc378a3b579d46ed89a2677769a6d5ea24 Mon Sep 17 00:00:00 2001
From: Benedict <benedict@0xb8000.de>
Date: Tue, 22 Mar 2016 19:11:22 +0100
Subject: completed set 2 challenge 11

---
 lib/lib.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 42 insertions(+), 8 deletions(-)

(limited to 'lib/lib.c')

diff --git a/lib/lib.c b/lib/lib.c
index 0eb5be8..7c8beae 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -81,7 +81,6 @@ static void three_bytes_to_base64(char * encode, int bytes_to_print, char *resul
 	// last six bit11s
 	four = encode[2] & 0x3F;
 	ret[3] = base64_encode[four];
-	ret[4] = '\0';
 	if(bytes_to_print-- > 0)
 		result[3] = ret[3];
 }
@@ -378,12 +377,11 @@ static int frequent_histogramm_matchs(char *string, int length)
  * encode the given string into base64 and stores it in result
  */
 
-void encode_to_base64(char *encode, char *result)
+void encode_to_base64(char *encode, int length_encode, char *result)
 {
-	int length = strlen(encode);
 	
-	int rounds = length / 3;
-	int bytes_last_round = length % 3;
+	int rounds = length_encode / 3;
+	int bytes_last_round = length_encode % 3;
 	int i;
 
 	for (i=0;i<rounds;i++) {
@@ -391,11 +389,15 @@ void encode_to_base64(char *encode, char *result)
 	}
 	// in der letzen runde nicht mehr alle ausgeben
 	// nur noch 3-leftover
+	result[rounds*4] = '\0';
+
 	if (bytes_last_round > 0) {
-		three_bytes_to_base64(encode + i*3, 1+bytes_last_round, &result[i*4]);
+		three_bytes_to_base64(&encode[i*3], (4-bytes_last_round), &result[i*4]);
 
-		for(i=0;i<(3-bytes_last_round);i++)
-			result[i*4+(1+bytes_last_round)] = '=';
+		for(i=bytes_last_round;i>=0;i--)
+			result[rounds*4+(4-bytes_last_round)] = '=';
+
+		result[rounds*4+4] = '\0';
 	}
 
 }
@@ -522,3 +524,35 @@ int read_base64_file(const char *file, char **out)
 	return file_pos;
 
 }
+
+int count_equal_blocks(char *string, int length_string, int blocksize)
+{
+	int number_blocks = length_string / blocksize;
+	printf("number_blocks: %i", number_blocks);
+	int hits = 0, i, j, k;
+
+	for(i=0;i<number_blocks;i++) {
+		for(j=1;j<number_blocks;j++) {
+			for(k=0;k<blocksize;k++) {
+				if(string[i*blocksize+k] != string[j*blocksize+k])
+					break;
+				if ( k == (blocksize-1))
+					hits++;
+			}
+		}
+	}
+	printf("hits:%i\n", hits);
+	return hits;
+
+}
+	
+int string_is_ecb_encrypted(char *string, int length_string, int blocksize)
+{
+	/**
+	 * equal cleartext blocks results in equal ciphertext blocks
+	 * in ECB mode, so basically we are just counting equal blocks...
+	 */
+	return (count_equal_blocks(string, length_string, blocksize) > (length_string/blocksize));
+}
+
+
-- 
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