Security Equipment Integration Working Group (SEIWG) Specification 012

Overview
The Security Equipment Integration Working Group (SEIWG) Specification 012 establishes the requirements for the performance, design, manufacture, test and acceptance for the Magnetic Stripe Credential (MSC) prime item. The SEIWG-012 specification states that a 40-digit credential or "unique identifier" should be encoded on all access control cards that contain a magnetic stripe.

The unique identifier is in the form of a 40-digit numbering scheme. This specification initially only pertained to magnetic stripe cards because these cards were the only cards that had sufficient storage capacity to comply with the specification. As smart card technology became more prevalent, the SEIWG-012 specification was applied to it as well. Smart card technology is capable of securely storing the 40-digit credential and smart card readers are capable of securely reading the information from the card.

Source

 * Government Smart Card Handbook, at 31-32.