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Designing Security Architecture Solutions phần 5

này để đi đến một quyết định một yêu cầu truy cập cụ thể ("X có thể đọc B?" "Có"). Chúng ta có thể xem mỗi quyết định truy cập như kết hợp tất cả dữ liệu có sẵn để đi đến một danh sách các quy tắc kiểm soát truy cập và áp dụng một quá trình ra quyết định để thiết lập các quy tắc. | Trusted Code 163 The infrastructure requirements of Authenticode are also required by Netscape s object signing solution software publishing policy and management PKI and all the attendant services and key distribution and life-cycle management. Signed Self-Decrypting and Self-Extracting Packages The last mechanism for trusting downloaded content is a catch-all clause to support distributed software delivery through any means not just through Web browsers. The content can be any arbitrary collection of bits and can be used for any arbitrary purpose. We need the ability to securely download software packages in many circumstances. We can purchase application software online and have it digitally delivered. We can download operating system patches that require high privileges to execute correctly. We might need authoritative and trusted data files containing information such as authoritative DNS mappings stock quotes legal contracts configuration changes or firmware patches for Internet appliances. Digitally delivered software can be dangerous. How should we ensure the integrity of a download Using digital downloads requires some level of trust. We must be sure of the source and integrity of a file before we install a patch update a DNS server sign a legal document or install a new firmware release. The same methods of using public-key technology apply here. Software must be digitally signed but might also require encryption because we do not want unauthorized personnel to have access to valuable code. Secure software delivery solutions use public and symmetric-key cryptography to digitally sign and encrypt packages in transit. The order of signing and encrypting is important. Anderson and Needham note in AN95 that a digital signature on an encrypted file proves nothing about the signer s knowledge of the contents of the file. If the signer is not the entity that encrypts the package the signer could be fooled into validating and certifying one input and digitally .