FDES: Fast DES in LMI Lambda Microcode

Back in the 80s, Bob Baldwin was hacking cryptography at MIT and one hack he built was a streamlined DES implementation which tried to trim as many clock cycles as possible to do a DES encryption. Unix machines were using a salted DES password hashing scheme with a hardcoded constant of 64 zero bits that was encrypted 25 times. In traditional Unix crypt(3), the salt—a 12-bit value derived from a 2-character ASCII string—permutes the expansion function E in the DES algorithm, swapping 24 bits of the round expansion so that hardware DES chips couldn't be used to accelerate password cracking. Bob wrote a C implementation of the Unix crypt(3) DES that was fast enough to run a dictionary attack on a password file in a few hours. This got me inspired. The LMI Lambda processor had basically the same data paths as the CADR and the TI Explorer; in fact, both the Lambda and Explorer had a CADR compatibility mode so that they could run exactly the same microcode. Like the CADR, the ALU took…