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The Release Authority can be manual or automated. The manual control of messages could be used if the need for increased control were required. Because it will be automated in Phase 2, the Release Authority filters will be set. These filters are used to automatically review message traffic.
Filters can perform checks on each message [e.g., ASCII E-mail only, label required, restrict senders, restrict recipients, restrict hosts, authorized attachments only (text file, WordPerfect 6.0 for Windows, etc.), restrict source routes, and perform word searches]. If a message does not pass the filter checks, the message can be returned to sender, returned to postmaster, returned to sender and postmaster, or destroyed. The filter and their functions are described below.
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6.5.1 | Message Security Protocol Filter |
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6.5.2 | Envelope Filter |
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6.5.3 | Message Filter |
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6.5.4 | Dirty Word Search Filter |
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6.5.5 | Manual Reviewer Filter |
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6.5.1 Message Security Protocol Filter
When activated, the Message Security Protocol (MSP) filter is responsible for processing all mail messages for MSP-compliance (i.e., signed or signed/encrypted). The filter verifies that the message is MSP-compliant, that the message has had the correct security processing applied, and that the person signing the message is authorized to pass messages through the SNS. The MSP filter requires the use of the Fortezza card and the PCMCIA card reader. For the other filters to properly process a message, the message must be forwarded from the MSP filter without a digital signature and in plain text format. Because the SNS must decrypt and inspect MSP-encrypted messages, it is considered a recipient of the message.
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The Envelope filter defines the hosts, senders, and recipients that will be allowed to transfer mail through the SNS. The Envelope filter can also check to see if a mail message has been sent using SMTP source routes and will reject the mail message if source routing is not allowed. Messages sent using source routing present a possible security risk to networks protected by the SNS. Source routing can be used to attack specific workstations on the high side of an SNS network.
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The Message filter places certain restrictions on the mail messages that pass through the SNS. In particular, the Message filter can be configured to check for the following message characteristics: printable ASCII E-mail; classification label; and authorized file attachment types such as text files prepared with Windows software (e.g., Lotus 1-2-3, Excel, PowerPoint, Word, WordPerfect, Harvard Graphics, and PerFORM PRO), DOS executables, and Windows executables.
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6.5.4 Dirty Word Search Filter
The Dirty Word Search filter scans mail messages for text containing security-sensitive (dirty) words. Words and phrases that are defined as sensitive by local site security policy are included in a dirty word list for use by the filter. If a message is found to contain a dirty word, the message will be rejected by the filter.
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Messages received by the Manual Reviewer filter will be forwarded to the manual review queue. There they will be reviewed by the Release Authority. Mail messages can also be forwarded to the manual review queue even if the Manual Reviewer filter is disabled. Messages rejected by one of the other four filters will be automatically forwarded to the manual review queue if the Manual Review Upon Reject field is specified as "On" for that filter.
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The CAW, which is a part of the Certification Authority (CA) hierarchy, will be used to provide directory information to the Directory System Agent and the Mail List Agent. Fortezza cards being tested in the Oak Ridge Testbed were programmed by NSA, but a CAW will be required for the NN-50 Demonstration LANs.
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