anchor.diff:  
     postPatch = ''
       cp README.md README
  +
  +    ${optionalString withPkcs11 ''
  +      substituteInPlace rngd.c \
  +        --replace /usr/lib64/opensc-pkcs11.so ${opensc}/lib/opensc-pkcs11.so
  +    ''}
     '';
   
     nativeBuildInputs = [ autoreconfHook libtool pkgconfig ];
  
positive.code:   buildInputs = [ sysfsutils ]
      ++ optionals withGcrypt        [ libgcrypt ]
      ++ optionals withJitterEntropy [ jitterentropy ]
      ++ optionals withNistBeacon    [ openssl curl libxml2 ]
      ++ optionals withPkcs11        [ libp11 openssl ];
  
    # This shouldn't be necessary but is as of 6.7
  
negative.code:   # Not sure if jitterentropy is safe to use for cryptography
    # and thus a default entropy source
  , jitterentropy ? null, withJitterEntropy ? false
  , libp11 ? null, opensc ? null, withPkcs11 ? true
  }:
  
  with stdenv.lib;
  