Ballot SMC017v2: Increase Minimum RSA CA Key Size

Overview

• This ballot proposes updates to the S/MIME Baseline Requirements based on Version 1.0.14.
• It increases the minimum RSA key size for Root and Subordinate CA certificates from 2048 bits to 4096 bits for keys created after September 15, 2026.
• It retains the 2048-bit minimum RSA key size for Subscriber certificates.
• It requires CAs to stop issuing Subscriber certificates from certain legacy RSA Subordinate CAs by September 15, 2027.
• It also includes minor typographic corrections.

Proposed requirement changes

• New Root or Subordinate CA RSA keys must be at least 4096 bits beginning September 15, 2026.
• For keys corresponding to CA certificates, including Root, Subordinate, and Cross Certificates, signed on or after September 15, 2026, the modulus size must be at least 4096 bits.
• For keys corresponding to Subscriber certificates, the modulus size must remain at least 2048 bits.
• Effective September 15, 2027, a CA must not issue certificates from any CA when all of these conditions are true:
  • the certificate contains id-kp-emailProtection in extKeyUsage
  • the certificate contains a subjectAltName extension that complies with Section 7.1.4.2.1
  • the CA certificate RSA key modulus size is less than 3072 bits
• The linked redline notes that this is intended to prevent issuance of S/MIME Subscriber certificates by existing Subordinate CAs with RSA keys smaller than 3072 bits, while still permitting issuance of Delegated OCSP Signing Certificates by those CAs.

Other edits

• The ballot includes typographic corrections, including capitalization changes for Curve25519 and Curve448.

Procedure status

• The ballot is described as a proposed Final Maintenance Guideline.
• The evidence shows only the discussion period, from June 16, 2026 at 18:00:00 UTC to June 23, 2026 at 18:00:00 UTC.
• No voting period, voting result, or Intellectual Property Review outcome is provided in the evidence.