You can use the PeopleSoft classes to encrypt and decrypt values.
To Encrypt a value:
Local JavaObject &SPCipherIn = CreateJavaObject("com.peoplesoft.pt.integrationgateway.common.EncryptPassword");
&vte = "valuetoencrypt";
&encryptedValue = &SPCipherIn.encryptPassword(&vte);
To Decrypt a value:
Local JavaObject &SPCipherOut = CreateJavaObject("psft.pt8.pshttp.PSCipher");
&decryptedValue = &SPCipherOut.decodePassword(&encryptedValue);