CREATE FUNCTION my_secret_key()
RETURNS int8 IMMUTABLE
AS $$
    SELECT 1234567890987654321
$$ LANGUAGE sql;

CREATE SEQUENCE userid_plaintext_seq;

CREATE TABLE users (
    userid bigint NOT NULL
        DEFAULT pgspeck_encrypt32(nextval('userid_plaintext_seq'), my_secret_key()),
    PRIMARY KEY (userid)
);

=# INSERT INTO users DEFAULT VALUES RETURNING *;
   userid
------------
 3497276207
(1 row)

INSERT 0 1
=# INSERT INTO users DEFAULT VALUES RETURNING *;
   userid
------------
 1514490635
(1 row)

INSERT 0 1

-- Encrypts a 32-bit plaintext using a 64-bit key.  Only the lowermost 32 bits
-- of the plaintext are used.  For the key, the full 64-bit range is effective.
CREATE FUNCTION pgspeck_encrypt32(plaintext int8, key int8)
	RETURNS int8
	AS 'pgspeck', 'pgspeck_encrypt32' LANGUAGE c STRICT;

-- Decrypts a value encrypted with pgspeck_encrypt32.
CREATE FUNCTION pgspeck_decrypt32(ciphertext int8, key int8)
	RETURNS int8
	AS 'pgspeck', 'pgspeck_decrypt32' LANGUAGE c STRICT;

-- Encrypts a 48-bit plaintext using a 96-bit key.  Only the lowermost 48 bits
-- of each key component can be non-zero.
CREATE FUNCTION pgspeck_encrypt48(plaintext int8, key1 int8, key2 int8)
	RETURNS int8
	AS 'pgspeck', 'pgspeck_encrypt48' LANGUAGE c STRICT;

-- Decrypts a value encrypted with pgspeck_encrypt48.
CREATE FUNCTION pgspeck_decrypt48(ciphertext int8, key1 int8, key2 int8)
	RETURNS int8
	AS 'pgspeck', 'pgspeck_decrypt48' LANGUAGE c STRICT;