chacha8: add a key generation variant that take a pointer and size

src/crypto/chacha8.h

@@ -70,13 +70,17 @@ namespace crypto {
     chacha8(data, length, reinterpret_cast<const uint8_t*>(&key), reinterpret_cast<const uint8_t*>(&iv), cipher);
   }
 
-  inline void generate_chacha8_key(std::string password, chacha8_key& key) {
+  inline void generate_chacha8_key(const void *data, size_t size, chacha8_key& key) {
     static_assert(sizeof(chacha8_key) <= sizeof(hash), "Size of hash must be at least that of chacha8_key");
     char pwd_hash[HASH_SIZE];
-    crypto::cn_slow_hash(password.data(), password.size(), pwd_hash);
+    crypto::cn_slow_hash(data, size, pwd_hash);
     memcpy(&key, pwd_hash, sizeof(key));
     memset(pwd_hash, 0, sizeof(pwd_hash));
   }
+
+  inline void generate_chacha8_key(std::string password, chacha8_key& key) {
+    return generate_chacha8_key(password.data(), password.size(), key);
+  }
 }
 
 #endif