diff --git a/README.md b/README.md
index 2a55bc2..953db89 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,11 @@ Calculate the required length for a `ciphertext` from `plaintext` Buffer.
 
 Number of bytes written into `ciphertext` at last call to `tx.encrypt`
 
+### `tx.destroy()`
+
+Destroys the internal state and zero all memory. Can only be called once,
+you may never call `encrypt` after and sets `.bytes` to `null`.
+
 ### `var rx = secretstream.decrypt(header, key)`
 
 Create an decrypt instance with `key`, using `header` from `encrypt`.
@@ -90,6 +95,11 @@ compared against one of the exported tags. Please review the [libsodium
 documentation](https://download.libsodium.org/doc/secret-key_cryptography/secretstream#usage)
 for how tags should be interpreted.
 
+### `rx.destroy()`
+
+Destroys the internal state and zero all memory. Can only be called once,
+you may never call `encrypt` after and sets `.bytes` and `.tag` to `null`.
+
 ## Install
 
 ```sh
diff --git a/example.js b/example.js
index 8a6e938..2468b68 100644
--- a/example.js
+++ b/example.js
@@ -18,3 +18,6 @@ var rx = secretstream.decrypt(header, key)
 var plaintext = rx.decrypt(ciphertext)
 
 console.log(plaintext.equals(Buffer.from('Hello world!')), rx.decrypt.tag.equals(secretstream.TAG_MESSAGE))
+
+rx.destroy()
+tx.destroy()
diff --git a/index.js b/index.js
index a763458..fea1870 100644
--- a/index.js
+++ b/index.js
@@ -18,10 +18,13 @@ exports.encrypt = function (header, key) {
   assert(Buffer.isBuffer(key), 'key must be Buffer')
   assert(key.byteLength >= exports.KEYBYTES, 'key must be at least KEYBYTES (' + exports.KEYBYTES + ') long')
 
+  var destroyed = false
   var state = sodium.crypto_secretstream_xchacha20poly1305_state_new()
   sodium.crypto_secretstream_xchacha20poly1305_init_push(state, header, key)
 
   function encrypt (tag, plaintext, ad, ciphertext, offset) {
+    assert(destroyed === false, 'state already destroyed')
+    assert(Buffer.isBuffer(plaintext), 'plaintext must be Buffer')
     if (ciphertext == null) ciphertext = Buffer.alloc(encryptionLength(plaintext))
     if (offset == null) offset = 0
 
@@ -33,12 +36,23 @@ exports.encrypt = function (header, key) {
   encrypt.bytes = 0
 
   function encryptionLength (plaintext) {
+    assert(Buffer.isBuffer(plaintext), 'plaintext must be Buffer')
+
     return plaintext.byteLength + exports.ABYTES
   }
 
+  function destroy () {
+    assert(destroyed === false, 'state already destroyed')
+    state = null // Should memzero when we have buffer trick in sodium-native
+    encrypt.bytes = null
+
+    destroyed = true
+  }
+
   return {
     encrypt,
-    encryptionLength
+    encryptionLength,
+    destroy
   }
 }
 
@@ -49,10 +63,13 @@ exports.decrypt = function (header, key) {
   assert(Buffer.isBuffer(key), 'key must be Buffer')
   assert(key.byteLength >= exports.KEYBYTES, 'key must be at least KEYBYTES (' + exports.KEYBYTES + ') long')
 
+  var destroyed = false
   var state = sodium.crypto_secretstream_xchacha20poly1305_state_new()
   sodium.crypto_secretstream_xchacha20poly1305_init_pull(state, header, key)
 
   function decrypt (ciphertext, ad, plaintext, offset) {
+    assert(destroyed === false, 'state already destroyed')
+    assert(Buffer.isBuffer(ciphertext), 'ciphertext must be Buffer')
     if (plaintext == null) plaintext = Buffer.alloc(decryptionLength(ciphertext))
     if (offset == null) offset = 0
 
@@ -65,11 +82,23 @@ exports.decrypt = function (header, key) {
   decrypt.bytes = 0
 
   function decryptionLength (ciphertext) {
+    assert(Buffer.isBuffer(ciphertext), 'ciphertext must be Buffer')
+
     return ciphertext.byteLength - exports.ABYTES
   }
 
+  function destroy () {
+    assert(destroyed === false, 'state already destroyed')
+    state = null // Should memzero when we have buffer trick in sodium-native
+    decrypt.tag = null
+    decrypt.bytes = null
+
+    destroyed = true
+  }
+
   return {
     decrypt,
-    decryptionLength
+    decryptionLength,
+    destroy
   }
 }