repeated "denial of existence" phrase in abstract could flow more smoothly.

[vttale]

Proposed, change:

"The Domain Name System Security (DNSSEC) Extensions introduced the
NSEC resource record (RR) for authenticated denial of existence and
the NSEC3 RR for hashed authenticated denial of existence. This
document introduces NSEC5 as an alternative mechanism for DNSSEC
authenticated denial of existence. "

to:

"The Domain Name System Security (DNSSEC) Extensions introduced the
NSEC resource record (RR) for authenticated denial of existence and
the NSEC3 RR for hashed authenticated denial of existence. This
document introduces NSEC5 as an alternative mechanism for DNSSEC
denials. "

Having "denial of existence" repeated three times in two sentences feels prosaically cumbersome to me.