cryptopals_c

commit 96b7d3b9962f77398553b0784b044845dc82c8af
parent 3d2a2afbcc28da6f736c4e1bd5c18558a5d909cc
Author: anna <anna@brokenlove.online>
Date:   Thu, 29 Aug 2024 20:46:48 +0200

c6 finished - might be a lil buggy idc

Diffstat:
M
s1/c6.c
 | 
91
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-

1 file changed, 90 insertions(+), 1 deletion(-)
diff --git a/s1/c6.c b/s1/c6.c
@@ -5,6 +5,88 @@
 
 const char b64table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
+float i_c(ba *ct)
+{
+	unsigned int occur[256];
+	unsigned int i;
+	unsigned int t;
+	float res;
+
+	res = 0;
+	memset(occur, 0, sizeof(occur));
+
+	for (i = 0; i < ct->len; i++)
+		occur[ct->val[i]]++;
+
+	t = 0;
+	for (i = 0; i < 256; i++)
+		t += occur[i] * (occur[i] - 1);
+
+	res = t / (float) (ct->len * (ct->len - 1));
+	return res;
+}
+
+float get_i_c_m(ba *ct, unsigned int m)
+{
+	float res;
+	int i;
+	res = 0;
+	for (i = 0; i < m; i++) {
+		ba *chunk = (ba *) malloc(sizeof(ba));
+		int j;
+		int k;
+
+		chunk->len = ct->len / m;
+		chunk->val = (uint8_t *) malloc(sizeof(uint8_t) * chunk->len);
+		
+		for (j = 0, k = 0; j <chunk->len &&  k + i < ct->len; j++, k += m)
+			chunk->val[j] = ct->val[k + i];
+		res += i_c(chunk);
+	}
+	return res / m;
+}
+
+unsigned int guess_m(ba *ct)
+{
+	unsigned int best;
+	float max;
+	int m;
+
+	max = 0;
+	for (m = 1; m < 40; m++) {
+		float avg;
+		
+		avg = get_i_c_m(ct, m);
+		if (avg > max) {
+			max = avg;
+			best = m;
+		}
+	}
+	return best;
+}
+
+void break_m(ba *ct, unsigned int m)
+{
+	int i;
+
+	for (i = 0; i < m; i++) {
+		ba *chunk = (ba *) malloc(sizeof(ba));
+		int j;
+		int k;
+
+		chunk->len = ct->len / m;
+		chunk->val = (uint8_t *) malloc(sizeof(uint8_t) * chunk->len);
+		
+		for (j = 0, k = 0; j <chunk->len &&  k + i < ct->len; j++, k += m)
+			chunk->val[j] = ct->val[k + i];
+
+		chunk = decrypt_scxor(chunk);
+
+		for (j = 0, k = 0; j <chunk->len &&  k + i < ct->len; j++, k += m)
+			 ct->val[k + i] = chunk->val[j];
+	}
+}
+
 int b64_chunk_to_hex(char **hex, char *b64)
 {
 	unsigned int val;
@@ -76,8 +158,15 @@ int main(int argc, char *argv[])
 
 	base64_to_hex(&hex, b64);
 	ct = ba_from_hex(hex);	
-	ba_fprint(ct, stdout, 0);
+	
+	int m = guess_m(ct);
+
+	break_m(ct, m);
+
+	ba_fprint_ascii(ct, stdout, 0);
 	printf("\n");
 
+	ba_free(ct);
 	fclose(f);
+	return 0;
 }