Decrypt jenkins encrypted value

gistfile1.txt

Go to https://jenkinsurl.com/script and run : 
println(hudson.util.Secret.decrypt("{encrypted_value}"))

To get the encrypted_value, go to the credential page, click on update and after do inspect element on the password field. Take the "value" property of the field. It should be between curly braces.

To get ALL the credentials : 
def creds = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
    com.cloudbees.plugins.credentials.common.StandardUsernameCredentials.class,
    Jenkins.instance,
    null,
    null
)

for(c in creds) {
  if(c instanceof com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey){
    println(String.format("id=%s desc=%s key=%s\n", c.id, c.description, c.privateKeySource.getPrivateKeys()))
  }
  if (c instanceof com.cloudbees.plugins.credentials.impl.UsernamePasswordCredentialsImpl){
    println(String.format("id=%s desc=%s user=%s pass=%s\n", c.id, c.description, c.username, c.password))
  }
}