add AES Encrypt Decrypt file stream example

_examples/aes_decrypt_file.md

@@ -0,0 +1,91 @@
+### AES Decrypt File example
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "crypsi.h"
+
+int write_file(char const* path, unsigned char* buffer, int buffer_size);
+char* load_file(char const* path, long* length_dst);
+
+int main(int argc, char** argv) {
+
+    unsigned char key_128[17] = "abc$#128djdyAgbj";
+    key_128[sizeof(key_128)-1] = 0x0; 
+
+    unsigned char key_192[25] = "abc$#128djdyAgbjau&YAnmc";
+    key_192[sizeof(key_192)-1] = 0x0; 
+
+    unsigned char key_256[33] = "abc$#128djdyAgbjau&YAnmcbagryt5x";
+    key_256[sizeof(key_256)-1] = 0x0; 
+
+    long burger_encrypted_stream_length = 0;
+
+    // load file
+    unsigned char* burger_encrypted_stream = load_file("./testdata/burger_aes_128_gcm_encrypted.bin", &burger_encrypted_stream_length);
+
+    unsigned char* dst;
+    int dst_len;
+
+    if(crypsi_aes_128_gcm_decrypt(key_128, burger_encrypted_stream, burger_encrypted_stream_length, &dst, &dst_len) != 0) {
+        printf("decrypt with aes error\n");
+        free((void*) dst);
+        free((void*) burger_encrypted_stream);
+        return -1;
+    }
+
+    if (write_file("./testdata/burger_out.png", dst, dst_len) != 0) {
+      printf("writing decrypted data to file error\n");
+      free((void*) dst);
+      free((void*) burger_encrypted_stream);
+      return -1;
+    }
+
+    printf("decrypted data written to the file\n");
+
+    free((void*) dst);
+    free((void*) burger_encrypted_stream);
+
+    return 0;
+}
+
+char* load_file(char const* path, long* length_dst) {
+    char* buffer = 0;
+    long length;
+    FILE * f = fopen (path, "rb");
+
+    if (f != NULL) {
+      fseek (f, 0, SEEK_END);
+      length = ftell (f);
+      fseek (f, 0, SEEK_SET);
+      buffer = (char*) malloc((length+1)*sizeof(char));
+      if (buffer) {
+        fread(buffer, sizeof(char), length, f);
+      }
+
+      fclose(f);
+    }
+
+    buffer[length] = 0x0;
+    *length_dst = length;
+
+    return buffer;
+}
+
+int write_file(char const* path, unsigned char* buffer, int buffer_size) {
+    long length;
+    FILE * f = fopen (path, "wb");
+
+    if (f != NULL) {
+      if (buffer) {
+        fwrite(buffer, sizeof(char), buffer_size, f);
+      }
+
+      fclose(f);
+      return 0;
+    }
+
+    return -1;
+}
+```

_examples/aes_encrypt_file.md

@@ -0,0 +1,91 @@
+### AES Encrypt File example
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "crypsi.h"
+
+int write_file(char const* path, unsigned char* buffer, int buffer_size);
+char* load_file(char const* path, long* length_dst);
+
+int main(int argc, char** argv) {
+
+    unsigned char key_128[17] = "abc$#128djdyAgbj";
+    key_128[sizeof(key_128)-1] = 0x0; 
+
+    unsigned char key_192[25] = "abc$#128djdyAgbjau&YAnmc";
+    key_192[sizeof(key_192)-1] = 0x0; 
+
+    unsigned char key_256[33] = "abc$#128djdyAgbjau&YAnmcbagryt5x";
+    key_256[sizeof(key_256)-1] = 0x0; 
+
+    long burger_stream_length = 0;
+
+    // load file
+    unsigned char* burger_stream = load_file("./testdata/burger.png", &burger_stream_length);
+
+    unsigned char* dst;
+    int dst_len;
+
+    if(crypsi_aes_128_gcm_encrypt(key_128, burger_stream, burger_stream_length, &dst, &dst_len) != 0) {
+        printf("encrypt with aes error\n");
+        free((void*) dst);
+        free((void*) burger_stream);
+        return -1;
+    }
+
+    if (write_file("./testdata/burger_aes_128_gcm_encrypted.bin", dst, dst_len) != 0) {
+      printf("writing encrypted data to file error\n");
+      free((void*) dst);
+      free((void*) burger_stream);
+      return -1;
+    }
+
+    printf("encrypted data written to the file\n");
+
+    free((void*) dst);
+    free((void*) burger_stream);
+
+    return 0;
+}
+
+char* load_file(char const* path, long* length_dst) {
+    char* buffer = 0;
+    long length;
+    FILE * f = fopen (path, "rb");
+
+    if (f != NULL) {
+      fseek (f, 0, SEEK_END);
+      length = ftell (f);
+      fseek (f, 0, SEEK_SET);
+      buffer = (char*) malloc((length+1)*sizeof(char));
+      if (buffer) {
+        fread(buffer, sizeof(char), length, f);
+      }
+
+      fclose(f);
+    }
+
+    buffer[length] = 0x0;
+    *length_dst = length;
+
+    return buffer;
+}
+
+int write_file(char const* path, unsigned char* buffer, int buffer_size) {
+    long length;
+    FILE * f = fopen (path, "wb");
+
+    if (f != NULL) {
+      if (buffer) {
+        fwrite(buffer, sizeof(char), buffer_size, f);
+      }
+
+      fclose(f);
+      return 0;
+    }
+
+    return -1;
+}
+```