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- Current PEPPOL AS2 specification 1.01 references RFC 3851 - S/MIME 3.1 Message Specification
- RFC 3851 (dated July 2004) allows for SHA2 algorithms, but only on a voluntary basis
- https://www.ietf.org/rfc/rfc3851.txt
- RFC 5751 (dated Jan 2010) obsoletes RFC 3851 - S/MIME 3.2 Message Specification:
- https://tools.ietf.org/html/rfc5751
- It mandates the use of SHA 256 and makes the support for SHA1 and MD5 optional
- The names of the MIC algorithms changes (RFC 3851: "sha256"; RFC 5751: "sha-256"), so it's easy to identify what version is used
- All changes from RFC 3851 are documented in chapter 1.6 - https://tools.ietf.org/html/rfc5751#section-1.6
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