cryptopals_c

commit 03eb6a68660664fdc45934404d1b3a06cc23d51c
parent 9fa92a533c32c17354fee573638b41920f24551f
Author: anna <anna@brokenlove.online>
Date:   Fri, 26 Jul 2024 23:54:44 +0200

c2 fixups, c3 done

Diffstat:
M
s1/c2.c
 | 
30
+++++++++++++++---------------
A
s1/c3.c
 | 
45
+++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 60 insertions(+), 15 deletions(-)
diff --git a/s1/c2.c b/s1/c2.c
@@ -1,19 +1,19 @@
 #include <ba.h> /* see my tools repo for this */
 
 int main(int argc, char* argv[]) {
-    if(argc != 3)
-        return -1;
-    ba* a;
-    ba* b;
-    a = ba_from_hex(argv[1]);
-    b = ba_from_hex(argv[2]);
-    if (a == NULL || b == NULL) {
-        return -1;
-    }
-    ba_xor(a, b);
-    ba_fprint(a, stdout, 0);
-    printf("\n");
-    ba_free(a);
-    ba_free(b);
-    return 0;
+	if (argc != 3)
+		return -1;
+	ba* a;
+	ba* b;
+	a = ba_from_hex(argv[1]);
+	b = ba_from_hex(argv[2]);
+	if (a == NULL || b == NULL) {
+		return -1;
+	}
+	ba_xor(a, b);
+	ba_fprint(a, stdout, 0);
+	printf("\n");
+	ba_free(a);
+	ba_free(b);
+	return 0;
 }
diff --git a/s1/c3.c b/s1/c3.c
@@ -0,0 +1,45 @@
+#include <ba.h>
+#include <stdlib.h>
+#include <ctype.h>
+
+int score_english(ba *text)
+{
+	int res = 0;
+	for (int i = 0; i < text->len; i++)
+		res += isalnum((text->val)[i]) || isspace((text->val)[i]);
+	return res;
+}
+
+int main(int argc, char* argv[]) {
+	if (argc != 2)
+		return -1;
+
+	ba *ct;
+	ba *key;
+	ct = ba_from_hex(argv[1]);
+	uint8_t best_key;
+	int max = 0;
+	if (!ct)
+		return -1;
+	printf("decrypting...\n");
+	for (uint16_t i = 0; i < 0xff; i++) {
+		char buf[2*(ct->len)];
+		snprintf(buf, 16, "%2x", i);
+		key = ba_from_hex_n(buf, ct->len);
+		ba_xor(key, ct);
+		int sc = score_english(key);
+		if (sc > max) {
+			max = sc;
+			best_key = i;
+		}
+	}
+
+	char buf[2*(ct->len)];
+	snprintf(buf, 16, "%2x", best_key);
+	key = ba_from_hex_n(buf, ct->len);
+	ba_xor(key, ct);
+	ba_fprint_ascii(key, stdout, 0);
+	printf("\n");
+
+	ba_free(ct);
+}