diff --git a/problems/09.md b/problems/09.md
index c86fb01..11d8185 100644
--- a/problems/09.md
+++ b/problems/09.md
@@ -7,23 +7,45 @@
 // sign.js
 var sodium = require('sodium-native')
 
+var args = process.argv
+
+if (args.length !== 3) {
+  console.log(`Usage: node sign.js "<message>"`)
+  process.exit()
+}
+
+var message = Buffer.from(args[2])
+
 var publicKey = Buffer.alloc(sodium.crypto_sign_PUBLICKEYBYTES)
 var secretKey = Buffer.alloc(sodium.crypto_sign_SECRETKEYBYTES)
 sodium.crypto_sign_keypair(publicKey, secretKey)
 
-var message = Buffer.from('Hello world!')
 var signature = Buffer.alloc(sodium.crypto_sign_BYTES)
+sodium.crypto_sign_detached(signature, message, secretKey)
 
-sodium.crypto_sign_detached(signature, message, privateKey)
-
-console.log('Public key:': publicKey.toString('hex'))
-console.log('Message:': message.toString())
-console.log('Signature:': signature.toString('hex'))
+console.log(`Message: ${message}`)
+console.log(`Public key: ${publicKey.toString('hex')}`)
+console.log(`Signature: ${signature.toString('hex')}`)
 ```
 
 ```js
 // verify.js
+var sodium = require('sodium-native')
+
+var args = process.argv
+
+if (args.length !== 5) {
+  console.log(`Usage: node verify.js "<message>" <publicKey (hex)> <signature (hex)>`)
+  process.exit()
+}
+
+var message = Buffer.from(args[2])
+var publicKey = Buffer.from(args[3], 'hex')
+var signature = Buffer.from(args[4], 'hex')
+
+const isSignatureValid = sodium.crypto_sign_verify_detached(signature, message, publicKey)
 
+console.log(`Signature is ${isSignatureValid ? 'valid' : 'invalid'}.`)
 ```
 
 </details>