add hex_encode

docs/crypto.md

@@ -23,16 +23,32 @@ in case you need to know the size of the decoded data, otherwise you can just pa
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
 ```
 
+### hex_encode
+
+Encodes an array of bytes into a string in hex representation. For example, converts 
+`[0xDE, 0xAD, 0xBE, 0xEF]` into `"DEADBEEF"`. The returned string will always be in capital
+letters with no leading `0x`. User is responsible for the freeing of the returned string
+
+```c
+const char *hex_encode(const unsigned char *hex, size_t sz);
+
+// Example
+const char *s = hex_encode(h, 4);
+assert(strcmp(s, "DEADBEEF") == 0);
+free(s);
+```
+
 ### hex_decode
 
 Decodes a string of characters representing hexadecimal bytes into an array of `unsigned char`.
-For example, converts `"DEADBEEF"` into `[0xDE, 0xAD, 0xBE, 0xEF]`.
+For example, converts `"DEADBEEF"` into `[0xDE, 0xAD, 0xBE, 0xEF]`. User is reponsible for the
+freeing of the returned byte array
 
 ```c
 unsigned char *hex_decode(const char *orig, size_t *sz);
 
 // Example
-s = hex_decode("DEADBEEF", &s_sz);
+unsigned char *s = hex_decode("DEADBEEF", &s_sz);
 unsigned char h[4] = {
     0xDE, 0xAD, 0xBE, 0xEF
 };