There seems to be a bug biting crypt(3) on Lenny amd64. On such platforms when using crypt(3) with the traditional DES scheme you get a segmentation fault. You do not get this when using the Modular Crypt Format ($digit$ password hash style). Fortunately, for the problem I was facing, I located and used the crypt(3) implementation from the Seventh Edition Unix. It is available from The Unix Heritage Society thanks to Henry Spencer.