A standard conforming implementation of UUIDs in three lines.

uuid.c

// Surprisingly, a standard conforming implementation of UUIDs in three lines.

#include <stdlib.h>

static void generate_random_uuid(unsigned char uuid[16])
{	
	arc4random_buf(uuid, 16);

	// Version 4, Variant 1: http://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
	uuid[6] = (uuid[6] & 0x0F) | 0x40;
	uuid[8] = (uuid[8] & 0x3F) | 0x80;
}

uuid.sql

CREATE TABLE id (
	  id INTEGER PRIMARY KEY,
	uuid BLOB NOT NULL DEFAULT ( -- // Version 4, Variant 1
		randomblob(6) ||
		substr(X'404142434445464748494a4b4c4d4e4f', 1 + (abs(random()) % 16) , 1) ||
		randomblob(1) || 
		substr(X'a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9f', 
			1 + (abs(random()) % 64) , 1) ||
		randomblob(7)),
	urn GENERATED ALWAYS AS ( 'urn:uuid:' ||
		substr(lower(hex(uuid)), 1,8) || '-' || 
		substr(lower(hex(uuid)), 9,4) || '-' || 
		substr(lower(hex(uuid)),13,4) || '-' || 
		substr(lower(hex(uuid)),17,4) || '-' || 
		substr(lower(hex(uuid)),21)
	) VIRTUAL
);