5 files changed, 149 insertions, 1 deletions

diff --git a/extract_decoded_executable/build.sh b/extract_decoded_executable/build.sh
index 6af8971..7d0bc0d 100755
--- a/extract_decoded_executable/build.sh
+++ b/extract_decoded_executable/build.sh
@@ -1,7 +1,14 @@
 #!/usr/bin/env bash
 
+SEED=$(seq 1 10 | shuf --random-source=/dev/urandom | sed -z 's/\n//g')
+
+echo "Encryption seed: ${SEED}"
+
 gcc -Wall -Werror -pedantic -O2 -mavx2 -march=x86-64-v3 -std=gnu23 ./test_binary.c -o ./test_binary
+gcc -Wall -Werror -pedantic -O2 -mavx2 -march=x86-64-v3 -std=gnu23 -DSEED_VAL=${SEED} ./encrypter.c -o ./encrypter
+./encrypter
+rm ./encrypter
 xxd -g1 -p ./test_binary | sed -z 's/\n$/\"/;s/^/\"/;s/\n//g' > ./test_binary_hex.dat
 rm ./test_binary
-gcc -O2 -mavx2 -march=x86-64-v3 -std=gnu23 -DBIN_HEX=$(cat ./test_binary_hex.dat) ./extractor.c -o ./extractor
+gcc -O2 -mavx2 -march=x86-64-v3 -std=gnu23 -DSEED_VAL=${SEED} -DBIN_HEX=$(cat ./test_binary_hex.dat) ./extractor.c -o ./extractor
 rm ./test_binary_hex.dat
diff --git a/extract_decoded_executable/encrypter.c b/extract_decoded_executable/encrypter.c
new file mode 100644
index 0000000..34732cb
--- /dev/null
+++ b/extract_decoded_executable/encrypter.c
@@ -0,0 +1,70 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <math.h>
+#include <sys/stat.h>
+#include "rng.h"
+
+void encrypt_test_binary(){
+	init_rng();
+	unsigned char enc_key[256];
+	memset( (void*)&enc_key, 0, sizeof(enc_key) );
+	size_t k_size = 0;
+	for ( ; k_size < 256; k_size++ )
+		enc_key[k_size] = (unsigned char)get_random_int( 1, 255 );
+	struct stat test_bin_info;
+	memset( (void*)&test_bin_info, 0, sizeof(struct stat) );
+	if ( stat("./test_binary", &test_bin_info) == -1 ){
+		fprintf( stderr, "Failed to stat: %s\n", strerror(errno) );
+		return;
+	}
+	if ( !((test_bin_info.st_mode & S_IFMT) == S_IFREG) ){
+		fputs( "Error: test binary is not regular file\n", stderr );
+		return;
+	}
+	unsigned char *test_bin_bytes = (unsigned char*)calloc( (size_t)test_bin_info.st_size, sizeof(unsigned char) );
+	if ( test_bin_bytes == NULL ){
+		fprintf( stderr, "Error: failed to allocate memory for reading test binary: %s\n", strerror(errno) );
+		return;
+	}
+	int test_bin_fd = open( "./test_binary", O_RDONLY, 0755 );
+	if ( test_bin_fd == -1 ){
+		fprintf( stderr, "Error: failed to open test binary for encryption: %s\n", strerror(errno) );
+		free( test_bin_bytes );
+		return;
+	}
+	if ( read(test_bin_fd, (void*)test_bin_bytes, (size_t)test_bin_info.st_size) == -1 ){
+		fprintf( stderr, "Error: failed to read test binary bytes: %s\n", strerror(errno) );
+		close( test_bin_fd );
+		free( test_bin_bytes );
+		return;
+	}
+	close( test_bin_fd );
+	size_t encrypted_bytes = 0;
+	for ( ; encrypted_bytes < (size_t)test_bin_info.st_size; encrypted_bytes++ )
+		test_bin_bytes[encrypted_bytes] = test_bin_bytes[encrypted_bytes] ^ enc_key[(size_t)test_bin_info.st_size % 255];
+	test_bin_fd = open( "./test_binary", O_RDWR | O_CREAT | O_TRUNC );
+	if ( test_bin_fd == -1 ){
+		fprintf( stderr, "Error: failed to open test binary for writing: %s\n", strerror(errno) );
+		free( test_bin_bytes );
+		return;
+	}
+	if ( write(test_bin_fd, (const void*)test_bin_bytes, (size_t)test_bin_info.st_size) == -1 ){
+		fprintf( stderr, "Error: failed to write encrypted test binary: %s\n", strerror(errno) );
+		close( test_bin_fd );
+		free( test_bin_bytes );
+		return;
+	}
+	close( test_bin_fd );
+	free( test_bin_bytes );
+	return;
+}
+
+int main( int argc, char *const *args ){
+	encrypt_test_binary();
+	return 0;
+}
diff --git a/extract_decoded_executable/extractor.c b/extract_decoded_executable/extractor.c
index 3a53536..5bda48d 100644
--- a/extract_decoded_executable/extractor.c
+++ b/extract_decoded_executable/extractor.c
@@ -1,9 +1,25 @@
 #include <stdlib.h>
 #include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
 #include <errno.h>
 #include <unistd.h>
+#include <math.h>
 #include <fcntl.h>
 #include <string.h>
+#include "rng.h"
+
+void decrypt_decoded_bytes( unsigned char *encrypted_bytes, size_t byte_count ){
+	unsigned char dec_key[256];
+	memset( (void*)&dec_key, 0, sizeof(dec_key) );
+	size_t recv_key_size = 0;
+	for ( ; recv_key_size < 256; recv_key_size++ )
+		dec_key[recv_key_size] = (unsigned char)get_random_int( 1, 255 );
+	size_t c_byte = 0;
+	for ( ; c_byte < byte_count; c_byte++ )
+		encrypted_bytes[c_byte] = encrypted_bytes[c_byte] ^ dec_key[byte_count % 255];
+	return;
+}
 
 void extract_contained_binary(){
 	double bin_hex_div = (double)strlen((const char*)BIN_HEX) / 2;
@@ -33,6 +49,7 @@ void extract_contained_binary(){
 		}
 		decoded_bytes[dec_byte_pos] = decoded_byte;
 	}
+	decrypt_decoded_bytes( decoded_bytes, hex_byte_count );
 	int out_fd = open( "/tmp/test_output_binary", O_RDWR | O_CREAT, 0755 );
 	if ( out_fd == -1 ){
 		fprintf( stderr, "Error: failed to open /tmp/test_output_binary for writing: %s\n", strerror(errno) );
@@ -52,6 +69,7 @@ void extract_contained_binary(){
 }
 
 int main( int argc, char *const *args ){
+	init_rng();
 	extract_contained_binary();
 	return 0;
 }
diff --git a/extract_decoded_executable/rng.h b/extract_decoded_executable/rng.h
new file mode 100644
index 0000000..93fd317
--- /dev/null
+++ b/extract_decoded_executable/rng.h
@@ -0,0 +1,51 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+
+struct rngstate{
+	uint64_t state[16];
+	int idx;
+};
+
+static struct rngstate global_rng_state;
+
+void init_rng(){
+	uint64_t seed_val = (uint64_t)SEED_VAL;
+	size_t c_idx = 0;
+	for ( ; c_idx < 16; c_idx++ ){
+		seed_val = seed_val * 0x13371337;
+		seed_val = seed_val ^ (seed_val >> 16);
+		global_rng_state.state[c_idx] = seed_val;
+	}
+	return;
+}
+
+uint64_t get_rng_output(){
+	int c_idx = global_rng_state.idx;
+	const uint64_t next_state = global_rng_state.state[c_idx++];
+	uint64_t use_state = global_rng_state.state[c_idx &= 15];
+	use_state ^= use_state << 31;
+	use_state ^= use_state >> 16;
+	use_state ^= next_state ^ (next_state >> 31);
+	global_rng_state.state[c_idx] = use_state;
+	global_rng_state.idx = c_idx;
+	return use_state * 0x1337;
+}
+
+unsigned int get_random_int( unsigned int min, unsigned int max ){
+	if ( min >= max )
+		return min;
+	uint64_t nmax = 0xffffffffffffffff;
+	uint64_t ncount = (max - min) + 1;
+	uint64_t upper_limit = nmax - (nmax % ncount);
+	uint64_t rand_int = get_rng_output();
+	if ( rand_int > upper_limit ){
+		while ( rand_int > upper_limit )
+			rand_int = get_rng_output();
+	}
+	return (unsigned int)(rand_int % max) + min;
+}
diff --git a/extract_decoded_executable/test_binary.c b/extract_decoded_executable/test_binary.c
index 0ac5c4c..6e1b72f 100644
--- a/extract_decoded_executable/test_binary.c
+++ b/extract_decoded_executable/test_binary.c
@@ -1,5 +1,7 @@
 #include <stdlib.h>
 #include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
 #include <errno.h>
 #include <unistd.h>
 #include <string.h>