Simply encrypt and decrypt Strings in ruby.

encrypt_decrypt.rb

require 'openssl'
require 'base64'

# key and iv stored in configs, generated using:
# cipher = OpenSSL::Cipher::Cipher.new('AES-256-CBC').encrypt
# key = cipher.random_key
# iv = cipher.random_iv

def encrypt_id(key, iv, id)
  cipher = OpenSSL::Cipher::Cipher.new('AES-256-CBC').encrypt
  cipher.key = key
  cipher.iv = iv
  encrypted_binary = cipher.update(id.to_s(36)) + cipher.final
  Base64.urlsafe_encode64(encrypted_binary)
end

def decrypt_id(key, iv, eid)
  cipher = OpenSSL::Cipher::Cipher.new('AES-256-CBC').decrypt
  cipher.key = key
  cipher.iv = iv
  decrypted_binary = Base64.urlsafe_decode64(eid)
  (cipher.update(decrypted_binary) + cipher.final).to_i(36)
end

# example:
cipher = OpenSSL::Cipher::Cipher.new('AES-256-CBC').encrypt
key = cipher.random_key
iv = cipher.random_iv
id = 876345875645
eid = encrypt_id(key, iv, id)

decrypt_id('guess', eid)
decrypt_id(key, iv, eid)