$RCSfile$ – Ruby-space definitions that completes C-space funcs for X509 and subclasses


'OpenSSL for Ruby 2' project
Copyright (C) 2002  Michal Rokos <m.rokos@sh.cvut.cz>
All rights reserved.


This program is licenced under the same licence as Ruby.
(See the file 'LICENCE'.)



OpenSSL provides SSL, TLS and general purpose cryptography. It wraps the OpenSSL library.


All examples assume you have loaded OpenSSL with:

require 'openssl'

These examples build atop each other. For example the key created in the next is used in throughout these examples.


Creating a Key

This example creates a 2048 bit RSA keypair and writes it to the current directory.

key = OpenSSL::PKey::RSA.new 2048

open 'private_key.pem', 'w' do |io| io.write key.to_pem end
open 'public_key.pem', 'w' do |io| io.write key.public_key.to_pem end

Exporting a Key

Keys saved to disk without encryption are not secure as anyone who gets ahold of the key may use it unless it is encrypted. In order to securely export a key you may export it with a pass phrase.

cipher = OpenSSL::Cipher::Cipher.new 'AES-128-CBC'
pass_phrase = 'my secure pass phrase goes here'

key_secure = key.export cipher, pass_phrase

open 'private.secure.pem', 'w' do |io|
  io.write key_secure

OpenSSL::Cipher.ciphers returns a list of available ciphers.

Loading a Key

A key can also be loaded from a file.

key2 = OpenSSL::PKey::RSA.new File.read 'private_key.pem'
key2.public? # => true


key3 = OpenSSL::PKey::RSA.new File.read 'public_key.pem'
key3.private? # => false

Loading an Encrypted Key

OpenSSL will prompt you for your pass phrase when loading an encrypted key. If you will not be able to type in the pass phrase you may provide it when loading the key:

key4_pem = File.read 'private.secure.pem'
key4 = OpenSSL::PKey::RSA.new key4_pem, pass_phrase

RSA Encryption

RSA provides ecryption and decryption using the public and private keys. You can use a variety of padding methods depending upon the intended use of encrypted data.


Documents encrypted with the public key can only be decrypted with the private key.

public_encrypted = key.public_encrypt 'top secret document'

Documents encrypted with the private key can only be decrypted with the public key.

private_encrypted = key.private_encrypt 'public release document'


Use the opposite key type do decrypt the document

top_secret = key.public_decrypt public_encrypted

public_release = key.private_decrypt private_encrypted

PKCS #5 Password-based Encryption

PKCS #5 is a password-based encryption standard documented at RFC2898. It allows a short password or passphrase to be used to create a secure encryption key.

PKCS #5 uses a Cipher, a pass phrase and a salt to generate an encryption key.

pass_phrase = 'my secure pass phrase goes here'
salt = '8 octets'


First set up the cipher for encryption

encrypter = OpenSSL::Cipher::Cipher.new 'AES-128-CBC'
encrypter.pkcs5_keyivgen pass_phrase, salt

Then pass the data you want to encrypt through

encrypted = encrypter.update 'top secret document'
encrypted << encrypter.final


Use a new Cipher instance set up for decryption

decrypter = OpenSSL::Cipher::Cipher.new 'AES-128-CBC'
decrypter.pkcs5_keyivgen pass_phrase, salt

Then pass the data you want to decrypt through

plain = decrypter.update encrypted
plain << decrypter.final

X509 Certificates

Creating a Certificate

This example creates a self-signed certificate using an RSA key and a SHA1 signature.

name = OpenSSL::X509::Name.parse 'CN=nobody/DC=example'

cert = OpenSSL::X509::Certificate.new
cert.version = 2
cert.serial = 0
cert.not_before = Time.now
cert.not_after = Time.now + 3600

cert.public_key = key.public_key
cert.subject = name

Certificate Extensions

You can add extensions to the certificate with OpenSSL::SSL::ExtensionFactory to indicate the purpose of the certificate.

extension_factory = OpenSSL::X509::ExtensionFactory.new nil, cert

extension_factory.create_extension 'basicConstraints', 'CA:FALSE'
extension_factory.create_extension 'keyUsage',
extension_factory.create_extension 'subjectKeyIdentifier', 'hash'

Signing a Certificate

To sign a certificate set the issuer and use OpenSSL::X509::Certificate#sign with a digest algorithm. This creates a self-signed cert because we’re using the same name and key to sign the certificate as was used to create the certificate.

cert.issuer = name
cert.sign key, OpenSSL::Digest::SHA1.new

open 'certificate.pem', 'w' do |io| io.write cert.to_pem end

Loading a Certificate

Like a key, a cert can also be loaded from a file.

cert2 = OpenSSL::X509::Certificate.new File.read 'certificate.pem'

Verifying a Certificate

Certificate#verify will return true when a certificate was signed with the given public key.

raise 'certificate can not be verified' unless cert2.verify key

Certificate Authority

A certificate authority (CA) is a trusted third party that allows you to verify the ownership of unknown certificates. The CA issues key signatures that indicate it trusts the user of that key. A user encountering the key can verify the signature by using the CA’s public key.

CA Key

CA keys are valuable, so we encrypt and save it to disk and make sure it is not readable by other users.

ca_key = OpenSSL::PKey::RSA.new 2048

cipher = OpenSSL::Cipher::Cipher.new 'AES-128-CBC'

open 'ca_key.pem', 'w', 0400 do |io|
  io.write key.export(cipher, pass_phrase)

CA Certificate

A CA certificate is created the same way we created a certificate above, but with different extensions.

ca_name = OpenSSL::X509::Name.parse 'CN=ca/DC=example'

ca_cert = OpenSSL::X509::Certificate.new
ca_cert.serial = 0
ca_cert.version = 2
ca_cert.not_before = Time.now
ca_cert.not_after = Time.now + 86400

ca_cert.public_key = ca_key.public_key
ca_cert.subject = ca_name
ca_cert.issuer = ca_name

extension_factory = OpenSSL::X509::ExtensionFactory.new
extension_factory.subject_certificate = ca_cert
extension_factory.issuer_certificate = ca_cert

extension_factory.create_extension 'subjectKeyIdentifier', 'hash'

This extension indicates the CA’s key may be used as a CA.

extension_factory.create_extension 'basicConstraints', 'CA:TRUE', true

This extension indicates the CA’s key may be used to verify signatures on both certificates and certificate revocations.

extension_factory.create_extension 'keyUsage', 'cRLSign,keyCertSign', true

Root CA certificates are self-signed.

ca_cert.sign ca_key, OpenSSL::Digest::SHA1.new

The CA certificate is saved to disk so it may be distributed to all the users of the keys this CA will sign.

open 'ca_cert.pem', 'w' do |io|
  io.write ca_cert.to_pem

Certificate Signing Request

The CA signs keys through a Certificate Signing Request (CSR). The CSR contains the information necessary to identify the key.

csr = OpenSSL::X509::Request.new
csr.version = 0
csr.subject = name
csr.public_key = key.public_key
csr.sign key, OpenSSL::Digest::SHA1.new

A CSR is saved to disk and sent to the CA for signing.

open 'csr.pem', 'w' do |io|
  io.write csr.to_pem

Creating a Certificate from a CSR

Upon receiving a CSR the CA will verify it before signing it. A minimal verification would be to check the CSR’s signature.

csr = OpenSSL::X509::Request.new File.read 'csr.pem'

raise 'CSR can not be verified' unless csr.verify csr.public_key

After verification a certificate is created, marked for various usages, signed with the CA key and returned to the requester.

csr_cert = OpenSSL::X509::Certificate.new
csr_cert.serial = 0
csr_cert.version = 2
csr_cert.not_before = Time.now
csr_cert.not_after = Time.now + 600

csr_cert.subject = csr.subject
csr_cert.public_key = csr.public_key
csr_cert.issuer = ca_cert.subject

extension_factory = OpenSSL::X509::ExtensionFactory.new
extension_factory.subject_certificate = csr_cert
extension_factory.issuer_certificate = ca_cert

extension_factory.create_extension 'basicConstraints', 'CA:FALSE'
extension_factory.create_extension 'keyUsage',
extension_factory.create_extension 'subjectKeyIdentifier', 'hash'

csr_cert.sign ca_key, OpenSSL::Digest::SHA1.new

open 'csr_cert.pem', 'w' do |io|
  io.write csr_cert.to_pem

SSL and TLS Connections

Using our created key and certificate we can create an SSL or TLS connection. An SSLContext is used to set up an SSL session.

context = OpenSSL::SSL::SSLContext.new

SSL Server

An SSL server requires the certificate and private key to communicate securely with its clients:

context.cert = cert
context.key = key

Then create an SSLServer with a TCP server socket and the context. Use the SSLServer like an ordinary TCP server.

require 'socket'

tcp_server = TCPServer.new 5000
ssl_server = OpenSSL::SSL::SSLServer.new tcp_server, context

loop do
  ssl_connection = ssl_server.accept

  data = connection.gets

  response = "I got #{data.dump}"
  puts response

  connection.puts "I got #{data.dump}"

SSL client

An SSL client is created with a TCP socket and the context. SSLSocket#connect must be called to initiate the SSL handshake and start encryption. A key and certificate are not required for the client socket.

require 'socket'

tcp_client = TCPSocket.new 'localhost', 5000
ssl_client = OpenSSL::SSL::SSLSocket.new client_socket, context

ssl_client.puts "hello server!"
puts ssl_client.gets

Peer Verification

An unverified SSL connection does not provide much security. For enhanced security the client or server can verify the certificate of its peer.

The client can be modified to verify the server’s certificate against the certificate authority’s certificate:

context.ca_file = 'ca_cert.pem'
context.verify_mode = OpenSSL::SSL::VERIFY_PEER

require 'socket'

tcp_client = TCPSocket.new 'localhost', 5000
ssl_client = OpenSSL::SSL::SSLSocket.new client_socket, context

ssl_client.puts "hello server!"
puts ssl_client.gets

If the server certificate is invalid or context.ca_file is not set when verifying peers an OpenSSL::SSL::SSLError will be raised.






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