I've got a very old USB disk, on which there's a very old encrypted partition.

It mounts as /dev/sdb1

On a newish box (with cryptsetup 1.7.3), I can attach to it with:

cryptsetup -c aes-plain -s 128 -h sha256 create wdexternal /dev/sdb1

But on an older box with (cryptsetup 1.6.1), that results in a /dev/mapper/wdexternal that doesn't look like a filesystem (according to fsck)

I've also tried the old command:

cryptsetup open /dev/sdb1 wdexternal

which my notes tell me used to work back in the day, but that gives

Device /dev/sdb1 is not a valid LUKS device.

Anyone know what's going on/how to fix it/how to go about understanding the problem?