Update DANE-for-SMTP-how-to.md

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@ -17,8 +17,8 @@ This how-to is created by the Dutch Internet Standards Platform (the organizatio
- [Why use DANE for SMTP?](#why-use-dane-for-smtp-)
* [Risks of SMTP with opportunistic TLS](#risks-of-smtp-with-opportunistic-tls)
* [DANE addresses these risks](#dane-addresses-these-risks)
* [How about MTA-STS?](#how-about-mta-sts)
- [DANE TLSA record example](#dane-tlsa-record-example)
* [How about MTA-STS?](#how-about-mta-sts-)
- [DANE TLSA record structure](#dane-tlsa-record-structure)
- [Advantages of DANE explained by illustrations](#advantages-of-dane-explained-by-illustrations)
* [Mail delivery: TLS without DANE](#mail-delivery--tls-without-dane)
* [Mail delivery: TLS with MITM stripping TLS](#mail-delivery--tls-with-mitm-stripping-tls)
@ -108,21 +108,23 @@ In view of the foregoing and considering the facts that the Dutch NCSC [advises]
Note that MTA-STA and DANE can co-exists next to each other. They intentionally do not interfere.
# DANE TLSA record example
# DANE TLSA record structure
![](images/DANE-example-TLSA-record.png)
**Usage**: says something about the type of certificate that is used for this TLSA record.
2: intermediate / root certificate
3: end-entity certificate (also called 'host certificate' or 'server certificate')
0: PKIX-TA (not recommended / [not used for SMTP](https://tools.ietf.org/html/rfc7672#section-3.1.3))
1: PKIX-EE (not recommended / [not used for SMTP](https://tools.ietf.org/html/rfc7672#section-3.1.3))
2: DANE-TA: intermediate / root certificate (recommended)
3: DANE-EE: end-entity certificate (also called 'host certificate' or 'server certificate') (recommended)
**Selector**: this is about the scope of the fingerprint regarding this TLSA record.
0: fingerprint with regard to the full certificate
1: fingerprint with regard to the public key
0: fingerprint with regard to the full certificate (not recommended / [to be avoided](http://dnssec-stats.ant.isi.edu/~viktor/x3hosts.html))
1: fingerprint with regard to the public key (recommended)
**Matching-Type**: information about the hashing mechanism used for fingeeprint regarding this TLSA record.
0: no hasing, full information
1: SHA2-256 hash
2: SHA2-512 hash
0: no hasing, full information (not recommended / [to be avoided](https://tools.ietf.org/html/rfc7672#section-3.1.2))
1: SHA2-256 hash ([recommended](https://tools.ietf.org/html/rfc7672#section-3.1.1))
2: SHA2-512 hash (not recommended / [less supported](https://www.rfc-editor.org/rfc/rfc6698.html#section-6))
# Advantages of DANE explained by illustrations
## Mail delivery: TLS without DANE