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Cryptographic Security Architecture: Design and Verification phần 9

Pentium hiện tại III duy nhất nối tiếp khả năng số có thể được mở rộng cho một nguồn sao lưu đầu vào cho các ắc entropy bằng cách lưu trữ với mỗi bộ xử lý một giá trị duy nhất, không giống như các ID vi xử lý, không có thể được đọc bên ngoài mà là được sử dụng để điều khiển một số hình thức của máy phát điện tương đương với các máy phát điện X9.17 | 6.4 The cryptlib Generator 239 The existing Pentium III unique serial number capability could be extended to provide a backup source of input for the entropy accumulator by storing with each processor a unique value which unlike the processor ID cannot be read externally that is used to drive some form of generator equivalent to the X9.17-like generator used in the Capstone Fortezza generator supplementing the existing physical randomness source. In the simplest case one or more linear feedback shift registers LFSRs driven from the secret value would serve to supplement the physical source while consuming an absolute minimum of die real estate. Although the use of SHA-1 in the output protects the relatively insecure LFSRs an extra safety margin could be provided through the addition of a small amount of extra circuitry to implement an enhanced LFSR-based generator such as a stop-and-go generator 64 which like the basic LFSR generator can be implemented with a fairly minimal transistor count. In addition like various other generators this generator reveals a portion of its internal state every time that it is used because of the lack of a real PRNG post-processing stage. Since a portion of the generator state is already being discarded each time it is stepped it would have been better to avoid recycling the output data into the internal state. Currently two 32-bit blocks of previous output data are present in each set of internal state data. 6.4 The cryptlib Generator Now that we have examined several generator designs and the various problems that they can run into we can look at the cryptlib generator. This section mostly covers the random pool management and PRNG post-processing functionality the entropy accumulation process is covered in Section 6.5. 6.4.1 The Mixing Function The function used in this generator improves on the generally used style of mixing function by incorporating far more state than the 128 or 160 bits used by other code. The mixing function