handle string or buffer input for securing encryption key

index.js

@@ -20,7 +20,8 @@ class Crypto {
 
   encryptionKey (encryptionKey) {
     var key = sodium.sodium_malloc(sodium.crypto_secretbox_KEYBYTES)
-    if (encryptionKey) key.write(encryptionKey)
+    if (encryptionKey && Buffer.isBuffer(encryptionKey)) key.copy(encryptionKey)
+    else if (encryptionKey && typeof encryptionKey === 'string') key.write(encryptionKey)
     else sodium.randombytes_buf(key)
     return key
   }

test/index.test.js

@@ -30,13 +30,20 @@ describe('key generation', (context) => {
     next()
   })
 
-  context('encryptionKey(key)', (assert, next) => {
+  context('encryptionKey(string)', (assert, next) => {
     const key = crypto.encryptionKey(crypto.randomBytes(32).toString('hex'))
     assert.ok(key, 'Key successfully generated')
     assert.ok(key instanceof Buffer, 'key is a secure buffer')
     next()
   })
 
+  context('encryptionKey(buffer)', (assert, next) => {
+    const key = crypto.encryptionKey(crypto.randomBytes(32))
+    assert.ok(key, 'Key successfully generated')
+    assert.ok(key instanceof Buffer, 'key is a secure buffer')
+    next()
+  })
+
   context('accessKey()', (assert, next) => {
     const accessKey = crypto.accessKey()
     assert.ok(accessKey, 'Key successfully generated')