[ansible@ansible ~]$ ansible-vault encrypt secret.yaml
New Vault password: 
Confirm New Vault password: 
Encryption successful

[ansible@ansible ~]$ cat secret.yaml 
$ANSIBLE_VAULT;1.1;AES256
66306635613562363439353734343137346161353763636162383363616234303962616363336366
6633396663663462353864393231313461353532373531340a306333616563306133343332373335
61356334383632656432333538366262636261646233363661386638366533616537373034356263
3961353663633331320a383261663839376463396534313237323266306564623637613637373462
39646263383532356362353833393635613732653334646134613262313439313739353331333831
6332343031333734373935336338333638656661386636613730