Solve optional data signing task

Lab 2 - Certificates/README.md

@@ -299,3 +299,27 @@ Check the output:
 ```sh
 openssl x509 -in intermediate.cer -noout -text
 ```
+
+# Signing Data
+Create a file with secret content:
+```sh
+cd /root
+vi secret.txt
+```
+
+## Create Signature
+```sh
+# Create and encrypt hash of file
+openssl dgst -sha256 -sign /root/ca/private/ca.key.pem -out /tmp/hash.sha256 secret.txt
+# Convert hash file to base64
+openssl base64 -in /tmp/hash.sha256 -out secret.sig
+```
+
+## Verify Signature
+Under normal circumstances:
+```sh
+# Re-create hash file from base64
+openssl base64 -d -in secret.sig -out /tmp/hash.sha256
+# Check integrity of `secret.txt`
+openssl dgst -sha256 -verify /root/ca/ca.key.pem.pub -signature /tmp/hash.sha256 secret.txt
+```