DNS-based Authentication of Named Entities


DNS-based Authentication of Named Entities is an Internet security protocol to allow X.509 digital certificates, commonly used for Transport Layer Security, to be bound to domain names using Domain Name System Security Extensions.
It is proposed in as a way to authenticate TLS client and server entities without a certificate authority. It is updated with operational and deployment guidance in. Application specific usage of DANE is defined in for SMTP and for using DANE with Service records.

Rationale

TLS/SSL encryption is currently based on certificates issued by certificate authorities. Within the last few years, a number of CA providers suffered serious security breaches, allowing the issuance of certificates for well-known domains to those who don't own those domains. Trusting a large number of CAs might be a problem because any breached CA could issue a certificate for any domain name. DANE enables the administrator of a domain name to certify the keys used in that domain's TLS clients or servers by storing them in the Domain Name System. DANE needs the DNS records to be signed with DNSSEC for its security model to work.
Additionally DANE allows a domain owner to specify which CA is allowed to issue certificates for a particular resource, which solves the problem of any CA being able to issue certificates for any domain.
DANE solves similar problems as:
; Certificate Transparency : ensuring that rogue CAs cannot issue certificates without the permission of the domain holder without being detected
; DNS Certification Authority Authorization : limiting which CAs can issue certificates for a given domain
However, unlike DANE, those technologies have wide support from browsers.

Email encryption

Until recently, there has been no widely implemented standard for encrypted email transfer. Sending an email is security agnostic; there is no URI scheme to designate secure SMTP. Consequently, most email that is delivered over TLS uses only opportunistic encryption. Since DNSSEC provides authenticated denial of existence, DANE enables an incremental transition to verified, encrypted SMTP without any other external mechanisms, as described by. A DANE record indicates that the sender must use TLS.
Additionally, a draft exists for applying DANE to S/MIME, and standardises bindings for OpenPGP.

Support

Applications

The TLSA RR for a service is located at a DNS name that specifies certificate constraints should be applied for the services at a certain TCP or UDP port. At least one of the TLSA RRs must provide a validation for the certificate offered by the service at the specified address.
Not all protocols handle Common Name matching the same way. HTTP requires that the Common Name in the X.509 certificate provided by the service matches regardless of the TLSA asserting its validity. SMTP does not require the Common Name matches, if the certificate usage value is 3, but otherwise does require a Common Name match. It is important to verify if there are specific instructions for the protocol being used.

RR data fields

The RR itself has 4 fields of data, describing which level of validation the domain owner provides.
E.g. _25._tcp.somehost.example.com. TLSA 3 1 1 BASE64

Certificate usage

The first field after the TLSA text in the DNS RR, specifies how to verify the certificate.
RR points
to a trust anchor		RR points to an
end entity certificate,
i.e. a specific certificate
used in the TLS
Require PKIX validation01
PKIX path validation not required23

Selector

When connecting to the service and a certificate is received, the selector field specifies which parts of it should be checked.
The actual data to be matched given the settings of the other fields. This is a long "text string" of hexadecimal data.

Examples

The HTTPS certificate for www.ietf.org specifies to check the SHA-256 hash of the public key of the certificate provided, ignoring any CA.
_443._tcp.www.ietf.org. TLSA 3 1 1 0C72AC70B745AC19998811B131D662C9AC69DBDBE7CB23E5B514B56664C5D3D6
Their mail service has the same exact certificate and TLSA.
ietf.org. MX 0 mail.ietf.org.
_25._tcp.mail.ietf.org. TLSA 3 1 1 0C72AC70B745AC19998811B131D662C9AC69DBDBE7CB23E5B514B56664C5D3D6
Finally, the following example, does the same as the others, but does the hash calculation over the entire certificate.
_25._tcp.mail.alice.example. TLSA 3 0 1 AB9BEB9919729F3239AF08214C1EF6CCA52D2DBAE788BB5BE834C13911292ED9

Standards