sh expect $CRYPTTAB_TRIED (if [ "$CRYPTTAB_TRIED" -gt 0 ]; then) to be set so the following fails:
busybox sh /lib/cryptsetup/scripts/wget_or_ask "somepassphrase:https://example.org/encrypted_keyfile" > unencrypted_keyfile
the following works (but without passing by busybox):
CRYPTTAB_TRIED=0 /lib/cryptsetup/scripts/wget_or_ask "somepassphrase:https://example.org/encrypted_keyfile" > unencrypted_keyfile