# SixArm.com » Ruby »
XID excellent identifier
[](https://codeclimate.com/github/SixArm/sixarm_ruby_xid)
[](https://travis-ci.org/SixArm/sixarm_ruby_xid)
* Doc:
* Gem:
* Repo:
* Email: Joel Parker Henderson,
## Introduction
XID is an excellent identifier. The XID much like a UUID (Universally Unique Identifier) or GUID (Globally Unique Identifer).
Example:
XID.new
#=> "90f44e35a062479289ff75ab2abc0ed3"
What makes the XID excellent: a streamlined specfication, stronger security, speedier algorithms, and simple string comparisons.
XID specification:
* 128 bit.
* Completely random and generated with a secure random generator.
* The string representation is entirely hexidecimal: digits 0-9 and lowercase a-f.
For docs go to
Want to help? We're happy to get pull requests.
## Install quickstart
Install:
gem install sixarm_ruby_xid
Bundler:
gem "sixarm_ruby_xid", ">=3.4.0", "<4"
Require:
require "sixarm_ruby_xid"
## Install with security (optional)
To enable high security for all our gems:
wget http://sixarm.com/sixarm.pem
gem cert --add sixarm.pem
gem sources --add http://sixarm.com
To install with high security:
gem install sixarm_ruby_xid --trust-policy HighSecurity
## Details
Methods:
* `XID.new`: create an XID and initialize to a random string.
* `XID.new(s)`: create an XID and initialize to a given string.
* `XID.valid?`: is this XIDa valid, i.e. the correct format?
* `XID#valid?(s)`: is a string a valid XID, i.e. the correct format?
* `XID#digest`: return a SHA256 digest as a 64-character string.
* `XID.digest(s)`: return a SHA256 digest as a 64-character string.
* `XID.parse(s)`: parse any string with enough data to a new XID.
Notes:
* XID uses Ruby's SecureRandom methods for strong security.
* An XID is a Ruby string, so you can do any string methods on it.
## UUID comparison
The XID is much like a UUID:
* The XID and UUID are both 128 bit.
* The XID has one form. The UUID has multiple forms, known as variants and versions.
* The XID is completely random. The UUID may have non-random pieces, such as a MAC sequence, and a fixed bit for the variant and version.
* The XID specification requires the use of a secure random generator. The UUID has no guarantee, and some forms use predicatable sequences.
* The XID uses digits 0-9 and lowecase a-f. The UUID canoncical form uses dashes to separate sequencies, and may use uppercase or lowercase.
To format an XID in the style of a UUID canonical representation:
xid = "90f44e35a062479289ff75ab2abc0ed3"
xid.sub(/(.{8})(.{4})(.{4})(.{16})/,"#$1-#$2-#$3-#$4")
#=> "90f44e35-a062-4792-89ff75ab2abc0ed3"
Note: the result string is formatted like a UUID, but is not guaranteed to be valid UUID. This is because the XID is random, whereas the UUID specification requires a specific bit that indicates the UUID is random.
To format a UUID in the style of an XID:
uuid = "14fFE137-2DB2-4A37-A2A4-A04DB1C756CA"
uuid.gsub(/-/,"").downcase
#=> ""14f7e1372db24a37a2a4a04db1c756ca"
Note: the result string is formatted like a XID, but is not a valid XID. This is because there's no guarantee that the UUID was randomly generated using a secure random generator, and also because the UUID-4 specification requires a random UUID to set the third section's first digit to 4.
## Unix tooling
To generate an XID on a typical Unix system, one way is the hexdump command:
$ hexdump -n 16 -v -e '16/1 "%02x" "\n"' /dev/random
b29dd48b7040f788fd926ebf1f4eddd0
To digest an XID by using SHA256:
$ echo -n "b29dd48b7040f788fd926ebf1f4eddd0" | shasum -a 256
afdfb0400e479285040e541ee87d9227d5731a7232ecfa5a07074ee0ad171c64
## Database tooling
To store an XID in a database, one way is using a string field that is 32 characters long.
Some databases have specialize fields for 128 bit values, such as PostgreSQL and its UUID extensions. PostgreSQL states that a UUID field will accept a string that is lowercase and that omits dashes. PostgreSQL does not do any validity-checking on the UUID value. Thus it is viable to store an XID in a UUID field. Our team has a goal to create a PostgreSQL extension for the XID data type.