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+## [xchapolybox](https://git.zx2c4.com/xchapolybox/about/)
+
+by Jason A. Donenfeld
+
+_Warning: you probably shouldn't use this. It hasn't actually ever been used._
+
+This is a very simple "crypto box", meant for being included as a single C file inside your project. It presents an extremely simple API:
+
+### Constants
+
+  - `XCHAPOLYBOX_OVERHEAD_LEN`
+  - `XCHAPOLYBOX_KEY_LEN`
+
+### Functions
+
+  - `void xchapolybox_seal(uint8_t *dst, const uint8_t *src, size_t src_len, const uint8_t key[XCHAPOLYBOX_KEY_LEN]);`
+  - `bool xchapolybox_open(uint8_t *dst, const uint8_t *src, size_t src_len, const uint8_t key[XCHAPOLYBOX_KEY_LEN]);`
+  - `void xchapolybox_genkey(uint8_t key[XCHAPOLYBOX_KEY_LEN]);`
+
+### Example
+
+```c
+uint8_t key[XCHAPOLYBOX_KEY_LEN];
+uint8_t *output, *input, *input2;
+size_t input_len, output_len;
+
+xchapolybox_genkey(key);
+
+input = get_input_from_somewhere(&input_len);
+assert(input);
+output_len = input_len + XCHAPOLYBOX_OVERHEAD_LEN;
+output = malloc(output_len);
+assert(output);
+
+xchapolybox_seal(output, input, input_len, key);
+
+input2 = malloc(input_len);
+assert(input2);
+
+if (!xchapolybox_open(input2, output, output_len, key)) {
+    // Always remember to check the auth tag.
+    return -1;
+}
+assert(!memcmp(input, input2, input_len));
+```