UDF fingerprints are used to create strong Strong Internet Names (SINs). These are a DNS address that include a UDF fingerprint in one of the labels. The DNS prefix mm-- is used to identify a DNS label that represents a UDF fingerprint.
The presence of a UDF fingerprint in a DNS address other than the Top Level Domain is a security policy assertion that the corresponding address SHOULD be interpreted in the context of a security policy that is validated by the root of trust corresponding to the specified fingerprint. If the fingerprint is the Top Level Domain, this requirement becomes a MUST.
For example, Alice has the email security key with fingerprint MB2GK-6DUF5-YGYYL-JNY5E. She uses the following email addresses: