"Programming semantics for multiprogrammed computations" (at http://citeseer.ist.psu.edu/511286.html ) is the original capability paper.

This paper can also be found at http://www.lcs.mit.edu/publications/pubs/pdf/MIT-LCS-TR-023.pdf

CiteSeer seems to be giving a blank page for this, but http://citeseer.ist.psu.edu/dennis66programming.html is similar.

For the first link try http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.16.9948

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CategorySecurity CategorySecurityModel ObjectCapabilityModel