Vulnerability
In 1994, Matt Blaze published the paper Protocol Failure in the Escrowed Encryption Standard. It pointed out that the Clipper's escrow system has a serious vulnerability. The chip transmitted a 128-bit "Law Enforcement Access Field" (LEAF) that contained the information necessary to recover the encryption key. To prevent the software that transmitted the message from tampering with the LEAF, a 16-bit hash was included. The Clipper chip would not decode messages with an invalid hash; however, the 16 bit hash was too short to provide meaningful security. A brute force attack would quickly produce another LEAF value that would give the same hash but not yield the correct keys after the escrow attempt. This would allow the Clipper chip to be used as an encryption device, while disabling the key escrow capability.
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