Update to the Cryptographic Message Syntax (CMS) Algorithm Identifier Protection Attribute

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Table of Contents

1. Introduction

This document corrects a mistake in [RFC6211]. It corrects an error in definition of the id-aa-CMSAlgorithmProtection ASN.1 object identifier.¶

The IANA registry entry for this ASN.1 object identifier does not need to be updated; it has always been correct.¶

The authors are aware of two implementations of RFC 6211, but they did not interoperate because one used the ASN.1 object identifier from RFC 6211 and the other used the ASN.1 object identifier from the IANA registry.¶

The mistakes were reported in [Err9144] and [Err9145].¶

In addition, the body of the document says that the set of attributes will "include only one instance of the algorithm protection attribute." This requirement can be included in the ASN.1 defintion.¶

This update to RFC 6211 will hopefully resolve future interoperability troubles.¶

2. Update to Section 2 of RFC 6211

OLD:¶

       aa-cmsAlgorithmProtection ATTRIBUTE ::= {
           TYPE CMSAlgorithmProtection
           IDENTIFIED BY { id-aa-CMSAlgorithmProtection }
       }

   The following object identifier identifies the algorithm protection
   attribute:

       id-aa-CMSAlgorithmProtection OBJECT IDENTIFIER ::= { iso(1)
            member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) 52 }

NEW:¶

       aa-cmsAlgorithmProtection ATTRIBUTE ::= {
           TYPE CMSAlgorithmProtection
           COUNTS MAX 1
           IDENTIFIED BY id-aa-CMSAlgorithmProtect
       }

   The following object identifier identifies the algorithm protection
   attribute:

       id-aa-CMSAlgorithmProtect OBJECT IDENTIFIER ::= { iso(1)
            member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
            smime(16) aa(2) 52 }

3. Update to Appendix A of RFC 6211

OLD:¶

     aa-cmsAlgorithmProtection ATTRIBUTE ::= {
        TYPE CMSAlgorithmProtection
        IDENTIFIED BY { id-aa-cmsAlgorithmProtect }
     }

     id-aa-cmsAlgorithmProtect OBJECT IDENTIFIER ::= {
        iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
        pkcs9(9) 52 }

NEW:¶

     aa-cmsAlgorithmProtection ATTRIBUTE ::= {
           TYPE CMSAlgorithmProtection
           COUNTS MAX 1
           IDENTIFIED BY id-aa-CMSAlgorithmProtect
     }

     id-aa-cmsAlgorithmProtect OBJECT IDENTIFIER ::= {
        iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
        pkcs9(9) smime(16) aa(2) 52 }

4. IANA Considerations

No IANA registry updates are needed. The IANA registry is correct.¶

5. Security Considerations

The CMS attribute specified in [RFC6211] is designed to address the security issue of algorithm substitutions. That is, the originator uses one algorithm, an attacker modifies the message, and then the validator uses a different algorithm. The specified protection is not successful unless all implementers use the same ASN.1 object identifier for the attribute.¶

6. References

Acknowledgments

Thanks to Paul Timmel for being the first person to spot the error in [RFC6211].¶

Thanks to Corey Bonnell and Mike StJohns for their careful review and constructive comments. The document is much better because of their review.¶

Authors' Addresses