cryptopals_c

commit 3d2a2afbcc28da6f736c4e1bd5c18558a5d909cc
parent 6331d486eb989eb5819cd9845f77ae13629ce9b9
Author: anna <anna@brokenlove.online>
Date:   Tue, 27 Aug 2024 23:14:10 +0200

s1/c6: decode b64 to hex (and finally into ba)

Diffstat:
A
s1/c6.c
 | 
83
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 83 insertions(+), 0 deletions(-)
diff --git a/s1/c6.c b/s1/c6.c
@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <ba.h>
+#include <cryptanalysis.h>
+
+const char b64table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+int b64_chunk_to_hex(char **hex, char *b64)
+{
+	unsigned int val;
+	unsigned int sz;
+	unsigned int i;
+
+	if (strlen(b64) != 4)
+		return -1;
+
+	val = 0;
+	for (i = 0; i < 4; i++) {
+		int j = 0;
+		val <<= 6;
+
+		while (b64[i] != '=' && b64table[j] != b64[i])
+			j++;
+
+		val += j;
+	}
+
+	sz = 6 - 2 * ((b64[2] == '=') + (b64[3] == '='));
+	sz++;
+
+	*hex = (char *) malloc(sizeof(char) * sz);
+	snprintf(*hex, sz, "%0*x", sz - 1, val);
+	return 0;
+}
+
+int base64_to_hex(char **hex, char *b64)
+{
+	unsigned int len;
+
+	len = (strlen(b64) * 3 / 4) + 2;
+	*hex = (char *) malloc(sizeof(char *) * len);
+
+	for (int i = 0; i < strlen(b64)/4; i++) {
+		char b64_chunk[5];
+		char *hex_chunk;
+
+		b64_chunk[4] = '\0';
+		memcpy(b64_chunk, b64+4*i, 4);
+		b64_chunk_to_hex(&hex_chunk, b64_chunk);
+		strcat(*hex, hex_chunk);
+	}
+}
+
+/* use coincidence test to determine the key */
+int main(int argc, char *argv[])
+{
+	char line[256];
+	char *b64;
+	char *hex;
+	FILE *f;
+	ba *ct;
+	int sz;
+
+	b64 = (char *) malloc(sizeof(char));
+
+	f = fopen(argv[1], "r");
+	if (!f)
+		fprintf(stderr, "error opening file\n");
+
+	sz = 1;
+	while (fgets(line, sizeof(line), f)) {
+		sz += strlen(line) - 1;
+		b64 = (char *) realloc(b64, sz);
+		strncat(b64, line, strlen(line) - 1);
+	}
+
+	base64_to_hex(&hex, b64);
+	ct = ba_from_hex(hex);	
+	ba_fprint(ct, stdout, 0);
+	printf("\n");
+
+	fclose(f);
+}