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Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book:
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----------- Algorithms for Export
Algorithms for export out of the United States must be approved by the U.S. government (actually, by the NSA—see Section 25.1). It is widely believed that these export-approved algorithms can be broken by the NSA. Although no one has admitted this on the record, these are some of the things the NSA is rumored to privately suggest to companies wishing to export their cryptographic products: — Leak a key bit once in a while, embedded in the ciphertext. — “Dumb down” the effective key to something in the 30-bit range. For example, while the algorithm might accept a 100-bit key, most of those keys might be equivalent. — Use a fixed IV, or encrypt a fixed header at the beginning of each encrypted message. This facilitates a known-plaintext attack. — Generate a few random bytes, encrypt them with the key, and then put both the plaintext and the ciphertext of those random bytes at the beginning of the encrypted message. This also facilitates a known-plaintext attack. NSA gets a copy of the source code, but the algorithm’s details remain secret from everyone else. Certainly no one advertises any of these deliberate weaknesses, but beware if you buy a U.S. encryption product that has been approved for export. 10.2 Public-Key Cryptography versus Symmetric Cryptography...
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