/lib/partman/choose_partition/35crypto/choices is in ubiquity 2.18.7.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | #!/bin/sh
. /lib/partman/lib/crypto-base.sh
# Only show menu option if there is at least one partition that can be used
# as a physical volume for encryption
[ $(crypto_list_allowed | wc -l) -gt 0 ] || exit 0
db_metaget partman-crypto/text/configure_crypto description
printf "crypto\t%s\n" "$RET"
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