scope:

Introduction

The "JSON Web Signature (JWS)" [JWS] specification defines the JWS Signing Input as the input to the digital signature or Message Authentication Code (MAC) computation, with the value ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload)). While this works well in practice for many use cases, including those accommodating arbitrary payload values, other use cases have been described in which base64url-encoding the payload is unnecessary and/or an impediment to adoption, particularly when the payload is large and/or detached.

This specification introduces a new JWS Header Parameter value that generalizes the JWS Signing Input computation in a manner that makes base64url-encoding the payload selectable and optional. The primary set of use cases where this enhancement may be helpful are those in which the payload may be very large and where means are already in place to enable the payload to be communicated between the parties without modifications. Appendix F of [JWS] describes how to represent JWSs with detached content, which would typically be used for these use cases.

The advantages of not having to base64url-encode a large payload are that allocation of the additional storage to hold the base64urlencoded form is avoided and the base64url-encoding computation never has to be performed. In summary, this option can help avoid unnecessary copying and transformations of the potentially large payload, resulting in sometimes significant space and time improvements for deployments.