NSA Snooping Domestic Crypto

[John Young]

Debate on whether the NSA spies domestically on US 
persons appears to be "yes" according to USSID 18, dated 
July 23, 1993, which was obtained by the National Security 
Archive a while back, for which we offer an HTML:

  http://cryptome.org/nsa-ussid18.htm

Parts previously redacted concerning domestic surveillance 
are now  revealed, among them these provisions for acquiring 
and retaining indefinitely domestically acquired encipherments:

[Quote]

(2) Domestic communications reasonably believed to 
contain technical data base information may be retained 
for a period sufficient to allow a thorough exploitation and 
to permit access to data that are, or are reasonably believed
likely to become, relevant to a current or future foreign 
intelligence requirement. Sufficient duration may vary 
with the nature of the exploitation.   (S-CCO)

a. In the context of a cryptanalytic effort, maintenance of 
technical data bases requires retention of all communications 
that are enciphered or reasonably believed to contain secret 
meaning, and sufficient duration may consist of any period of 
time during which encrypted material is subject to, or of use
in, cryptanalysis. (S-CCO)

b. In the case of communications that are not enciphered or 
otherwise thought to contain secret meaning, sufficient duration 
is one year unless the Deputy Director for Operations, NSA, 
determines in writing that retention for a longer period is 
required to respond to authorized foreign intelligence or 
counterintelligence requirements. (S-CCO)

[End quote]

Again, these sections were censored in versions of USSID 18
previously made public, a 1980 version here:

  http://cryptome.org/nsa-ussid18-80.htm

While the quoted material is a small part of the 52-page
document, variations on it are repeated more than
once, and seems to be the one exception to the
requirement to avoid domestic interceptions and
to destroy any that are inadvertently acquired.

The classification (S-CCO) is not explained but some
think it perhaps indicates material limited to the UK/USA
agreement and/or the Echelon partners. A better answer
is welcomed.