module OpenSSL
OpenSSL provides SSL, TLS and general purpose cryptography. It wraps the OpenSSL library.
Examples¶ ↑
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.
Keys¶ ↑
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.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 end
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
or
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 encryption and decryption using the public and private keys. You can use a variety of padding methods depending upon the intended use of encrypted data.
Encryption & Decryption¶ ↑
Asymmetric public/private key encryption is slow and victim to attack in cases where it is used without padding or directly to encrypt larger chunks of data. Typical use cases for RSA encryption involve “wrapping” a symmetric key with the public key of the recipient who would “unwrap” that symmetric key again using their private key. The following illustrates a simplified example of such a key transport scheme. It shouldn't be used in practice, though, standardized protocols should always be preferred.
wrapped_key = key.public_encrypt key
A symmetric key encrypted with the public key can only be decrypted with the corresponding private key of the recipient.
original_key = key.private_decrypt wrapped_key
By default PKCS#1 padding will be used, but it is also possible to use other forms of padding, see PKey::RSA for further details.
Signatures¶ ↑
Using “private_encrypt” to encrypt some data with the private key is equivalent to applying a digital signature to the data. A verifying party may validate the signature by comparing the result of decrypting the signature with “public_decrypt” to the original data. However, OpenSSL::PKey already has methods “sign” and “verify” that handle digital signatures in a standardized way - “private_encrypt” and “public_decrypt” shouldn't be used in practice.
To sign a document, a cryptographically secure hash of the document is computed first, which is then signed using the private key.
digest = OpenSSL::Digest::SHA256.new signature = key.sign digest, document
To validate the signature, again a hash of the document is computed and the signature is decrypted using the public key. The result is then compared to the hash just computed, if they are equal the signature was valid.
digest = OpenSSL::Digest::SHA256.new if key.verify digest, signature, document puts 'Valid' else puts 'Invalid' end
PBKDF2 Password-based Encryption¶ ↑
If supported by the underlying OpenSSL version used, Password-based Encryption should use the features of PKCS5. If not supported or if required by legacy applications, the older, less secure methods specified in RFC 2898 are also supported (see below).
PKCS5 supports PBKDF2 as it was specified in PKCS#5 v2.0. It still uses a password, a salt, and additionally a number of iterations that will slow the key derivation process down. The slower this is, the more work it requires being able to brute-force the resulting key.
Encryption¶ ↑
The strategy is to first instantiate a Cipher for encryption, and then to generate a random IV plus a key derived from the password using PBKDF2. PKCS #5 v2.0 recommends at least 8 bytes for the salt, the number of iterations largely depends on the hardware being used.
cipher = OpenSSL::Cipher.new 'AES-128-CBC' cipher.encrypt iv = cipher.random_iv pwd = 'some hopefully not to easily guessable password' salt = OpenSSL::Random.random_bytes 16 iter = 20000 key_len = cipher.key_len digest = OpenSSL::Digest::SHA256.new key = OpenSSL::PKCS5.pbkdf2_hmac(pwd, salt, iter, key_len, digest) cipher.key = key Now encrypt the data: encrypted = cipher.update document encrypted << cipher.final
Decryption¶ ↑
Use the same steps as before to derive the symmetric AES key, this time setting the Cipher up for decryption.
cipher = OpenSSL::Cipher.new 'AES-128-CBC' cipher.decrypt cipher.iv = iv # the one generated with #random_iv pwd = 'some hopefully not to easily guessable password' salt = ... # the one generated above iter = 20000 key_len = cipher.key_len digest = OpenSSL::Digest::SHA256.new key = OpenSSL::PKCS5.pbkdf2_hmac(pwd, salt, iter, key_len, digest) cipher.key = key Now decrypt the data: decrypted = cipher.update encrypted decrypted << cipher.final
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. If possible, PBKDF2 as described above should be used if the circumstances allow it.
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'
Encryption¶ ↑
First set up the cipher for encryption
encrypter = OpenSSL::Cipher.new 'AES-128-CBC' encrypter.encrypt encrypter.pkcs5_keyivgen pass_phrase, salt
Then pass the data you want to encrypt through
encrypted = encrypter.update 'top secret document' encrypted << encrypter.final
Decryption¶ ↑
Use a new Cipher instance set up for decryption
decrypter = OpenSSL::Cipher.new 'AES-128-CBC' decrypter.decrypt 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 cert.add_extension extension_factory.create_extension('basicConstraints', 'CA:FALSE', true) cert.add_extension extension_factory.create_extension( 'keyUsage', 'keyEncipherment,dataEncipherment,digitalSignature') cert.add_extension extension_factory.create_extension('subjectKeyIdentifier', 'hash')
The list of supported extensions (and in some cases their possible values) can be derived from the “objects.h” file in the OpenSSL source code.
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 ca_key.export(cipher, pass_phrase) end
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 ca_cert.add_extension extension_factory.create_extension('subjectKeyIdentifier', 'hash')
This extension indicates the CA's key may be used as a CA.
ca_cert.add_extension 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.
ca_cert.add_extension 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 end
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 end
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 csr_cert.add_extension extension_factory.create_extension('basicConstraints', 'CA:FALSE') csr_cert.add_extension extension_factory.create_extension( 'keyUsage', 'keyEncipherment,dataEncipherment,digitalSignature') csr_cert.add_extension 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 end
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}" connection.close end
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.connect 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.connect 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.
Constants
- OPENSSL_FIPS
- OPENSSL_LIBRARY_VERSION
Version of OpenSSL the ruby OpenSSL extension is running with
- OPENSSL_VERSION
Version of OpenSSL the ruby OpenSSL extension was built with
- OPENSSL_VERSION_NUMBER
Version number of OpenSSL the ruby OpenSSL extension was built with (base 16)
- VERSION
OpenSSL ruby extension version
Public Class Methods
Returns a Digest subclass by
name
.
require 'openssl' OpenSSL::Digest("MD5") # => OpenSSL::Digest::MD5 Digest("Foo") # => NameError: wrong constant name Foo
# File ext/openssl/lib/openssl/digest.rb, line 81 def Digest(name) OpenSSL::Digest.const_get(name) end
static VALUE ossl_debug_get(VALUE self) { return dOSSL; }
Turns on or off CRYPTO_MEM_CHECK. Also shows some debugging message on stderr.
static VALUE ossl_debug_set(VALUE self, VALUE val) { VALUE old = dOSSL; dOSSL = val; if (old != dOSSL) { if (dOSSL == Qtrue) { CRYPTO_mem_ctrl(CRYPTO_MEM_CHECK_ON); fprintf(stderr, "OSSL_DEBUG: IS NOW ON!\n"); } else if (old == Qtrue) { CRYPTO_mem_ctrl(CRYPTO_MEM_CHECK_OFF); fprintf(stderr, "OSSL_DEBUG: IS NOW OFF!\n"); } } return val; }
See any remaining errors held in queue.
Any errors you see here are probably due to a bug in ruby's OpenSSL implementation.
VALUE ossl_get_errors() { VALUE ary; long e; ary = rb_ary_new(); while ((e = ERR_get_error()) != 0){ rb_ary_push(ary, rb_str_new2(ERR_error_string(e, NULL))); } return ary; }
Turns FIPS mode on or off. Turning on FIPS mode will obviously only have an effect for FIPS-capable installations of the OpenSSL library. Trying to do so otherwise will result in an error.
Examples¶ ↑
OpenSSL.fips_mode = true # turn FIPS mode on OpenSSL.fips_mode = false # and off again
static VALUE ossl_fips_mode_set(VALUE self, VALUE enabled) { #ifdef HAVE_OPENSSL_FIPS if (RTEST(enabled)) { int mode = FIPS_mode(); if(!mode && !FIPS_mode_set(1)) /* turning on twice leads to an error */ ossl_raise(eOSSLError, "Turning on FIPS mode failed"); } else { if(!FIPS_mode_set(0)) /* turning off twice is OK */ ossl_raise(eOSSLError, "Turning off FIPS mode failed"); } return enabled; #else if (RTEST(enabled)) ossl_raise(eOSSLError, "This version of OpenSSL does not support FIPS mode"); return enabled; #endif }
Private Instance Methods
Returns a Digest subclass by
name
.
require 'openssl' OpenSSL::Digest("MD5") # => OpenSSL::Digest::MD5 Digest("Foo") # => NameError: wrong constant name Foo
# File ext/openssl/lib/openssl/digest.rb, line 81 def Digest(name) OpenSSL::Digest.const_get(name) end