In general, the subject matter described in this specification relates to security credentials for documents, such as identification documents. One example is an identification document that includes a photographic image of an individual associated with the document, and a spiral pattern applied to a region of the identification document. The spiral pattern includes an elliptical spiral segmented into a plurality of arc segments, where wherein the arc segments of the spiral pattern encode identification data associated with the individual. Other implementations include corresponding processes, systems, apparatus, and computer programs related to generating and verifying identification documents with spiral patterns.