set7: task51: completed

1 files changed, 190 insertions, 0 deletions

diff --git a/set7/task51.c b/set7/task51.c
new file mode 100644
index 0000000..b380a0b
--- /dev/null
+++ b/set7/task51.c
@@ -0,0 +1,190 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include "../lib/lib7.h"
+#include <zlib.h>
+
+
+void generate_random_printable_bytes(char *s, unsigned int length)
+{
+	int i;
+
+	for(i=0;i<length;i++)
+		s[i] = random_number_between(33,127);
+}
+
+void format_request(char **res, char *content, char *secret)
+{
+	char *request_template =
+		"POST / HTTP/1.1\n"
+		"Host: hapless.com\n"
+		"Cookie: sessionid=%s\n"
+		"Content-Length: %i\n\n\n"
+		"%s";
+
+	// 10 for the content length as max
+	*res = malloc(strlen(request_template)+10+strlen(content)+strlen(secret));
+	sprintf(*res, request_template, secret, strlen(content), content);
+}
+
+void my_compress(char *toCompress, char **compressed, int *compressed_length)
+{
+	// 20 bytes for metadata and bla but normally it should be smaller
+	// than the uncompressed one
+	*compressed = malloc(strlen(toCompress)+20);
+	// compress
+	z_stream defstream;
+	defstream.zalloc = Z_NULL;
+	defstream.zfree = Z_NULL;
+	defstream.opaque = Z_NULL;
+
+	defstream.avail_in = strlen(toCompress);
+	defstream.next_in = toCompress;
+	defstream.avail_out = strlen(toCompress)+20;
+	defstream.next_out = *compressed;
+
+	deflateInit(&defstream, Z_BEST_COMPRESSION);
+	deflate(&defstream, Z_FINISH);
+	deflateEnd(&defstream);
+
+	*compressed_length = defstream.total_out;
+	//printf("uncompressed/compressed: %i/%i\n", strlen(toCompress), defstream.total_out);
+
+}
+int oracle_count = 0;
+
+int compression_oracle(char *content, char* secret, int stream_cipher)
+{
+	oracle_count++;
+	char *res;
+	char *compressed;
+	int compressed_length;
+	format_request(&res, content, secret);
+	//printf("%s\n", res);
+	my_compress(res, &compressed, &compressed_length);
+	// encrypt
+	// using AES_CTR, plaintext and ciphertext length are the same
+	// do it anyway
+	if(stream_cipher == 1) {
+		char *encrypted = malloc(compressed_length);
+		generate_random_bytes(key, 16);
+		generate_random_bytes(nonce, 16);
+		aes_ctr(compressed, compressed_length, encrypted, key, nonce);
+		return compressed_length;
+	}
+	else {
+		// do CBC encryption aka add padding
+		char *encrypted;
+		int pad_len = aes_cbc_padded(compressed, compressed_length, &encrypted,
+				key, iv, 1);
+		return pad_len;
+	}
+}
+
+int max_int_index(int *numbers, int length)
+{
+	int i;
+	int max = 0;
+	int index = 0;
+
+	for(i=0;i<length;i++) {
+		if(numbers[i] > max) {
+			max = numbers[i];
+			index = i;
+			}
+	}
+
+	return index;
+}
+
+int main()
+{
+	srand(time(NULL));
+	char *known_text = "Cookie: sessionid=";
+	char *secret = "TmV2ZXIgcmV2ZWFsIHRoZSBXdS1UYW5nIFNlY3JldCE=";
+	// generate password between 33, 127 
+	// assume here that the session id is printable (HTTP is text protocol)
+	char *t = malloc(strlen(known_text)+50);
+	memset(t, 0, strlen(known_text)+50);
+	memcpy(t, known_text, strlen(known_text));
+	int max, res, i, k;
+	
+	// assume that the string we wanne find is less than 100 bytes
+	for(k=0;k<100;k++) {
+		t[strlen(known_text)+k] = 0x09;
+		max = compression_oracle(t, secret, 1);
+		for(i=33;i<128;i++) {
+			t[strlen(known_text)+k] = (char) i;			
+			res = compression_oracle(t, secret, 1);
+			if(res < max)
+				break;
+		}
+		if(max == res)
+			break;
+	}
+
+	printf("found string : %s\n", t);
+	printf("should string: Cookie: sessionid=%s\n", secret);
+	// doing binary search above would reduce the calls to the orcale
+	// significant
+	printf("calls to the oracle: %i\n", oracle_count);
+	
+	
+	// with cbc
+	// length will always be a multiple of the block size
+	oracle_count = 0;
+	printf("with CBC mode\n");
+	// because we only get multiple of 16 as result we have to take
+	// care that a complete block gets compressed
+	// we than need control over the size of the request so that
+	// is is a multiple of 16 BEFORE padding
+	// otherwise we compress 15 bytes and use one block less
+	char *kt = malloc(strlen(known_text)+strlen(secret));
+	memcpy(kt, known_text, strlen(known_text));
+	memcpy(&kt[strlen(known_text)], secret, strlen(secret));
+	// one block which should be compressed away
+	// 6 is the alignment to get a full block
+	char rand[17+6];
+	char ttt[18+8];
+	int j,l;
+	generate_random_printable_bytes(rand, 16+8);
+	rand[17] = '\0';
+	char *raw_request;
+	char *compressed;
+	int compressed_length;
+	int pad;
+	int counts[127-33];
+	int times = 8;
+	char found_sec_cbc[100];
+
+	format_request(&raw_request, "AAAAAAAAAAAAAAAA", secret);
+	my_compress(raw_request, &compressed, &compressed_length);
+	__pkcs7_padding(compressed, compressed_length, 16, &pad);
+	int max_ = compression_oracle(rand, secret, 0);
+
+	memcpy(&ttt[pad], &known_text[strlen(known_text)-16], 16);
+	for(l=0;l<strlen(secret);l++) {
+		memset(&counts, 0, sizeof(int)*(127-33));
+		generate_random_printable_bytes(ttt, pad);
+		for(i=0;i<15;i++)
+			ttt[pad+i] = ttt[pad+i+1];
+		for(k=0;k<10;k++) {
+			for(i=33;i<127;i++) {
+				ttt[pad+15] = i;
+				ttt[pad+16] = '\0';
+				int len = compression_oracle(ttt, secret, 0);
+				if( len < max_)
+					break;
+			}
+			counts[i-33]++;
+		}
+		i = max_int_index(counts, 127-33);
+		found_sec_cbc[l] = (char) (i + 33);
+	}
+	found_sec_cbc[l] = '\0';
+	printf("should: %s\n", secret);
+	printf("is    : %s\n", found_sec_cbc);
+	printf("calls to the oracle: %i\n", oracle_count);
+}