All transaction information passed between merchant sites and Sage Pay’s systems is encrypted using 128-bit SSL certificates. No cardholder information is ever passed unencrypted and any messages sent to your servers from Sage Pay are signed using MD5 hashing to prevent tampering. You can be completely assured that nothing you pass to Sage Pay’s servers can be examined, used or modified by any third parties attempting to gain access to sensitive information.
All sensitive data is secured using the same internationally recognised 256-bit encryption standards used by, among others, the US Government. The encryption keys are held on state-of-the-art, tamper proof systems in the same family as those used to secure VeriSign's Global Root certificate, making them all but impossible to extract.
For full details of Sage Pay's Security Measures and how your payment is handled, please visit : http://www.sagepay.co.uk/policies/security-policy