You can use CryptoUtil
:
import com.kms.katalon.util.CryptoUtil
def originalText = 'mypassword'
println("Original text: ${originalText}")
def encryptedText = CryptoUtil.encode(CryptoUtil.getDefault(originalText))
println("Encrypted text: ${encryptedText}")
def decryptedText = (CryptoUtil.decode(CryptoUtil.getDefault(encryptedText)))
println("Decrypted text: ${decryptedText}")