xorcat

commit 3d2f9ccc6ebe61fea284a043513668dd77d324fb
Author: Louis Burda <quent.burda@gmail.com>
Date:   Mon,  5 Sep 2022 14:16:48 +0200

Allow key masking for bruteforce

Diffstat:
A
.gitignore
 | 
1
+
A
Makefile
 | 
8
++++++++
A
xorcat.c
 | 
109
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 118 insertions(+), 0 deletions(-)
diff --git a/.gitignore b/.gitignore
@@ -0,0 +1 @@
+xorcat
diff --git a/Makefile b/Makefile
@@ -0,0 +1,8 @@
+all: xorcat
+
+clean:
+	rm -f xorcat
+
+xorcat: xorcat.c
+
+.PHONY: all clean
diff --git a/xorcat.c b/xorcat.c
@@ -0,0 +1,109 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <err.h>
+
+static const char usage[] = "USAGE: xorcat KEYMASK";
+
+void
+die(const char *fmtstr)
+{
+	fprintf(stderr, "%s\n", fmtstr);
+	exit(1);
+}
+
+void
+xorcat(uint8_t *indata, size_t insize, uint8_t *key, size_t keylen)
+{
+	uint8_t writebuf[4098];
+	size_t i, nout, pos;
+
+	pos = 0;
+	while (pos < insize) {
+		for (i = 0; i < sizeof(writebuf) && i < insize - pos; i++)
+			writebuf[i] = indata[pos + i] ^ key[(pos + i) % keylen];
+		nout = write(STDOUT_FILENO, writebuf, i);
+		if (nout != i) err(1, "write");
+		pos += i;
+	}
+}
+
+uint8_t *
+collect(size_t *size)
+{
+	uint8_t readbuf[4098];
+	uint8_t *data;
+	size_t nread, cap;
+
+	cap = 4098;
+	data = malloc(cap);
+	if (!data) err(1, "malloc");
+
+	*size = 0;
+	while (1) {
+		nread = read(STDIN_FILENO, readbuf, sizeof(readbuf));
+		if (nread <= 0) break;
+		if (cap < *size + nread) {
+			cap *= 2;
+			data = realloc(data, cap);
+		}
+		memcpy(data + *size, readbuf, nread);
+		*size += nread;
+	}
+
+	return data;
+}
+
+int
+main(int argc, const char **argv)
+{
+	uint8_t *mask, *key;
+	size_t keylen;
+	uint8_t *indata;
+	size_t insize;
+	unsigned maskb;
+	ssize_t i;
+
+	if (argc != 2) die(usage);
+
+	if (strlen(argv[1]) % 2) die(usage);
+
+	keylen = strlen(argv[1]) / 2;
+	mask = calloc(keylen, 1);
+	key = calloc(keylen, 1);
+	if (!mask || !key) err(1, "malloc");
+
+	for (i = 0; i < keylen; i++) {
+		if (!strncmp(argv[1] + 2 * i, "??", 2)) {
+			mask[i] = 1;
+		} else {
+			if (!sscanf(argv[1] + 2 * i, "%02X", &maskb))
+				die("Bad mask");
+			mask[i] = (uint8_t) maskb;
+		}
+	}
+
+	indata = collect(&insize);
+	while (1) {
+		printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> ");
+		for (i = 0; i < keylen; i++)
+			printf("%02X", key[i]);
+		printf("\n");
+		fflush(stdout);
+
+		xorcat(indata, insize, key, keylen);
+
+		for (i = keylen - 1; i >= 0; i--) {
+			if (mask[i]) {
+				key[i] += 1;
+				if (key[i]) break;
+			}
+		}
+		if (i < 0) break;
+	}
+
+	free(key);
+	free(mask);
+}