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Updated DANE How to (markdown)

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Dennis Baaten 2019-04-12 16:38:23 +02:00
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DANE-How-to.md
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@ -20,65 +20,59 @@ This part of the How-to describes the steps that should be taken with regard to
* Mailserver is operational
## Generating DANE records
**primairy mailserver (mail1.example.com)**
**Primairy mailserver (mail1.example.com)**
Generate the DANE SHA-256 hash with `openssl x509 -in /path/to/primairy-mailserver.crt -noout -pubkey | openssl pkey -pubin -outform DER | openssl sha256`. This command results in the following output.
> (stdin)= 29c8601cb562d00aa7190003b5c17e61a93dcbed3f61fd2f86bd35fbb461d084
**secundairy mailserver (mail2.example.com)**
**Secundairy mailserver (mail2.example.com)**
For the secundairy mailserver we generate the DANE SHA-256 hash using
`openssl x509 -in /path/to/secundairy-mailserver.crt -noout -pubkey | openssl pkey -pubin -outform DER | openssl sha256`. This command results in the following output.
> (stdin)= 22c635348256dc53a2ba6efe56abfbe2f0ae70be2238a53472fef5064d9cf437
## Publishing DANE records
Configuration options
* Selector field is "1" because we used the certificates' public key to generate DANE hash/signature
* Usage is "3". In this case we generated a DANE hash of the leaf certificate itself. Therefore we use usage field "3" (DANE-EE: Domain Issued Certificate)
* Matching-type is "1" because we use SHA-256.
Now that we have the SHA-256 hashes, we can construct the DNS records. We make the following configuration choices:
* Usage field is "**3**"; we generated a DANE hash of the leaf certificate itself (DANE-EE: Domain Issued Certificate).
* Selector field is "**1**"; we used the certificates' public key to generate DANE hash/signature.
* Matching-type field is "**1**"; we use SHA-256.
With this information we can create a DNS record for DANE:
With this information we can create the DNS record for DANE:
`_25._tcp.mail.example.com. IN TLSA 3 1 1 29c8601cb562d00aa7190003b5c17e61a93dcbed3f61fd2f86bd35fbb461d084`
`_25._tcp.mail2.example.com. IN TLSA 3 1 1 22c635348256dc53a2ba6efe56abfbe2f0ae70be2238a53472fef5064d9cf437`
> _25._tcp.mail.example.com. IN TLSA 3 1 1 29c8601cb562d00aa7190003b5c17e61a93dcbed3f61fd2f86bd35fbb461d084
> _25._tcp.mail2.example.com. IN TLSA 3 1 1 22c635348256dc53a2ba6efe56abfbe2f0ae70be2238a53472fef5064d9cf437
## Generating DANE roll-over records
First we split the bundle file into multiple certificates.
`cat ca-bundle-file.crt | awk 'BEGIN {c=0;} /BEGIN CERT/{c++} { print > "bundlecert." c ".crt"}'`
In this case this results in two files: _bundlecert.1.crt_ and _bundlecert.2.crt_.
We use the provided bundle file for generating the DANE hashes belonging to the root certificate. In order to do that, we first split the bundle file into multiple certificates using `cat ca-bundle-file.crt | awk 'BEGIN {c=0;} /BEGIN CERT/{c++} { print > "bundlecert." c ".crt"}'`. In this specific case this results in two files: _bundlecert.1.crt_ and _bundlecert.2.crt_.
For each file we view the subject and the issuer.
Command
`openssl x509 -in bundlecert.1.crt -noout -subject -issuer`
For each file we view the **subject** and the **issuer**. We start with the first file using `openssl x509 -in bundlecert.1.crt -noout -subject -issuer`. This results in the following output.
Output
`subject=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA`
`issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority`
> subject=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA
Command
openssl x509 -in bundlecert.2.crt -noout -subject -issuer
Output
subject=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
> issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
The second certificate (bundlecert.2.crt) is the root certficate as the subject and the issuer are the same. Root certificates are self-signed, while intermediate certificates are signed by another certificate (being a root certificate, of another intermediate certificate).
For the second file we use `openssl x509 -in bundlecert.2.crt -noout -subject -issuer`. This results in the following output.
> subject=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
> issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
Based on the information of these two certificates, we can conclude that the second certificate (bundlecert.2.crt) is the root certificate; since root certificates are self-signed the **subject** and the **issuer** are the same. The other certificate (bundlecert.1.crt) is an intermediate certificate which is (in this case) signed by the root certificate.
## Publishing DANE roll-over records
In this case we select the root certificate as a roll-over anchor.
Because we prefer the root certificate to be our roll-over anchor, we generate the DANE SHA-256 hash using `openssl x509 -in bundlecert.2.crt -noout -pubkey | openssl pkey -pubin -outform DER | openssl sha256`. This results in the following output.
Command
`openssl x509 -in bundlecert.2.crt -noout -pubkey | openssl pkey -pubin -outform DER | openssl sha256`
> (stdin)= c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde
Output
`(stdin)= c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde`
Since both certificates for the primary and secondary come from the same Certificate Authority, they both have the same root certificate. So we don't have to repeat this with a different bundle file.
Configuration options
* Selector field is "1" because we use the certificate public key to generate DANE hash/signature
* Usage is "2". In this case I generated a DANE hash of a certificate in the chain the chain of trust, instead of the certificate itself. Therefore we use usage field "2" (DANE-TA: Trust Anchor Assertion)
* Matching-type is "1" because I use SHA-256.
Now that we have the SHA-256 hash, we can construct the DANE roll-over DNS records. We make the following configuration choices:
* Usage field is "**2**"; we generated a DANE hash of the root certificate which is in the chain the chain of trust of the actual leaf certificate (DANE-TA: Trust Anchor Assertion).
* Selector field is "**1**"; because we use the root certificate's public key to generate a DANE hash.
* Matching-type field is "**1**"; because we use SHA-256.
With this information we can create a rollover DNS record for DANE:
`_25._tcp.mail.traxotic.net. IN TLSA 2 1 1 c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde`
`_25._tcp.mail2.traxotic.net. IN TLSA 2 1 1 c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde`
> _25._tcp.mail.example.com. IN TLSA 2 1 1 c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde
> _25._tcp.mail2.example.com. IN TLSA 2 1 1 c784333d20bcd742b9fdc3236f4e509b8937070e73067e254dd3bf9c45bf4dde
## Configuring mailserver