Commits on Feb 20, 2024

1. Fix ASN.1 issues in PKCS#7 and S/MIME signing (pyca#10373) …

   * Fix ASN.1 for S/MIME capabilities.
   
   The current implementation defines the SMIMECapabilities attribute
   so that its value is a SEQUENCE of all the algorithm OIDs that are
   supported.
   However, the S/MIME v3 spec (RFC 2633) specifies that each algorithm
   should be specified in its own SEQUENCE:
   
   SMIMECapabilities ::= SEQUENCE OF SMIMECapability
   
   SMIMECapability ::= SEQUENCE {
      capabilityID OBJECT IDENTIFIER,
      parameters ANY DEFINED BY capabilityID OPTIONAL }
   
   (RFC 2633, Appendix A)
   
   This commit changes the implementation so that each algorithm
   is inside its own SEQUENCE. This also matches the OpenSSL
   implementation.
   
   * Fix the RSA OID used for signing PKCS#7/SMIME
   
   The current implementation computes the algorithm identifier used
   in the `digest_encryption_algorithm` PKCS#7 field
   (or `SignatureAlgorithmIdentifier` in S/MIME) based on both the
   algorithm used to sign (e.g. RSA) and the digest algorithm (e.g. SHA512).
   
   This is correct for ECDSA signatures, where the OIDs used include the
   digest algorithm (e.g: ecdsa-with-SHA512). However, due to historical
   reasons, when signing with RSA the OID specified should be the one
   corresponding to just RSA ("1.2.840.113549.1.1.1" rsaEncryption),
   rather than OIDs which also include the digest algorithm (such as
   "1.2.840.113549.1.1.13", sha512WithRSAEncryption).
   
   This means that the logic to compute the algorithm identifier is the
   same except when signing with RSA, in which case the OID will always
   be `rsaEncryption`. This is consistent with the OpenSSL implementation,
   and the RFCs that define PKCS#7 and S/MIME.
   
   See RFC 3851 (section 2.2), and RFC 3370 (section 3.2) for more details.
   
   * Add tests for the changes in PKCS7 signing
   
   * PKCS7 fixes from code review
   
   * Update CHANGELOG

   

   facutuesca authored and alex committed Feb 20, 2024
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