1 files changed, 98 insertions, 0 deletions
diff --git a/stegtoy/bmpencode.c b/stegtoy/bmpencode.c
new file mode 100644
index 0000000..731693a
--- /dev/null
+++ b/stegtoy/bmpencode.c
@@ -0,0 +1,98 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#define FLAG "UMASS{f1l3f0rm4754r3h4rd_r3m3mb3rh34r7bl33d}"
+
+int main(int argc, char **argv)
+{
+		struct stat st;
+		const char *path_in, *path_out, *data;
+		char *buf, *output, *flag;
+		size_t file_size, data_len;
+		FILE *fp;
+		int i;
+
+		int32_t data_start;
+		uint32_t compression, image_size;
+
+		flag = malloc(strlen(FLAG) + 1);
+		strcpy(flag, FLAG);
+
+		if (argc != 4) {
+				fprintf(stderr, "usage: %s [in] [out] [data]\n", argv[0]);
+				return 1;
+		}
+
+		path_in = argv[1]; path_out = argv[2]; data = argv[3];
+
+		stat(path_in, &st);
+		file_size = st.st_size;
+
+		buf = malloc(file_size);
+
+		fp = fopen(path_in, "rb");
+		if (fp == NULL) {
+				fprintf(stderr, "%s: no such file\n", path_in);
+				return 2;
+		}
+
+		fread(buf, file_size, 1, fp);
+		fclose(fp);
+
+		// Here's where the actual parsing
+		if (buf[0] != 'B' || buf[1] != 'M') {
+				fprintf(stderr, "%s: not a valid BMP\n", path_in);
+				return 3;
+		}
+
+		compression = *((uint32_t *) (buf + 0x1e));
+		if (compression != 0) {
+				fprintf(stderr, "%s: no support for compressed BMP\n", path_in);
+				return 4;
+		}
+
+		data_start = *((int32_t *) (buf + 0xa));
+		image_size = *((uint32_t *) (buf + 0x22));
+
+		output = malloc(0x6 + 0x28 + image_size);
+		output[0] = 'B'; // Header
+		output[1] = 'M';
+		*((uint32_t *) (output + 0x2)) = 0x6 + 0x28 + image_size; // File size
+		*((uint32_t *) (output + 0xa)) = 0x36; // Data start
+		*((uint32_t *) (output + 0xe)) = 0x28; // Header size
+		*((uint32_t *) (output + 0x12)) = *((uint32_t *) (buf + 0x12)); // Width
+		*((uint32_t *) (output + 0x16)) = *((uint32_t *) (buf + 0x16)); // Height
+		*((uint16_t *) (output + 0x1a)) = 1; // nb plan
+		*((uint16_t *) (output + 0x1c)) = 24; // bpp
+		*((uint32_t *) (output + 0x1e)) = 0; // compression
+		*((uint32_t *) (output + 0x22)) = image_size; // Image size
+
+		// Here's the vuln.
+		memcpy(output + 0x36, buf + data_start, image_size);
+
+		data_len = strlen(data);
+		for (i = 0; i < image_size - 8 && i < data_len; i += 8) {
+				output[0x36 + i + 0] = output[0x36 + i + 0] & 254 | ((data[i] & (1 << 7)) >> 7);
+				output[0x36 + i + 1] = output[0x36 + i + 1] & 254 | ((data[i] & (1 << 6)) >> 6);
+				output[0x36 + i + 2] = output[0x36 + i + 2] & 254 | ((data[i] & (1 << 5)) >> 5);
+				output[0x36 + i + 3] = output[0x36 + i + 3] & 254 | ((data[i] & (1 << 4)) >> 4);
+				output[0x36 + i + 4] = output[0x36 + i + 4] & 254 | ((data[i] & (1 << 3)) >> 3);
+				output[0x36 + i + 5] = output[0x36 + i + 5] & 254 | ((data[i] & (1 << 2)) >> 2);
+				output[0x36 + i + 6] = output[0x36 + i + 6] & 254 | ((data[i] & (1 << 1)) >> 1);
+				output[0x36 + i + 7] = output[0x36 + i + 7] & 254 | ((data[i] & (1 << 0)) >> 0);
+		}
+
+		fp = fopen(path_out, "wb+");
+		if (fp == NULL) {
+				fprintf(stderr, "%s: could not write\n", path_out);
+				return 5;
+		}
+		fwrite(output, 0x6 + 0x28 + image_size, 1, fp);
+		fclose(fp);
+
+		free(buf);
+		return 0;
+}