/usr/share/igtf-policy/classic/DarkMatterSecureCA.namespaces is in igtf-policy-classic 1.88-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#NAMESPACES-VERSION: 1.0
#
# @(#)secureca.namespaces
# CA alias    : DarkMatterSecureCA
#    subord_of: QuoVadis-Root-CA2G3
#    subjectDN: /C=AE/O=DarkMatter LLC/CN=DarkMatter Secure CA
#    hash     : secureca
#    (generated automatically from dmsecureca.signing_policy)
#
TO Issuer "/C=AE/O=DarkMatter LLC/CN=DarkMatter Secure CA" \
  PERMIT Subject "/C=AE/O=DarkMatterGrid/.*"
TO Issuer "/C=AE/O=DarkMatter LLC/CN=DarkMatter Secure CA" \
  PERMIT Subject "/DC=com/DC=DarkMatterGrid/.*"
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