# 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

    File.write 'private_key.pem', key.private_to_pem
    File.write 'public_key.pem', key.public_to_pem

### 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 password.

    cipher = OpenSSL::Cipher.new 'aes-256-cbc'
    password = 'my secure password goes here'

    key_secure = key.private_to_pem cipher, password

    File.write 'private.secure.pem', 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.read File.read 'private_key.pem'
    key2.public? # => true
    key2.private? # => true

or

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

### Loading an Encrypted Key¶ ↑

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

    key4_pem = File.read 'private.secure.pem'
    password = 'my secure password goes here'
    key4 = OpenSSL::PKey.read key4_pem, password

## 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.

    signature = key.sign 'SHA256', 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.

    if key.verify 'SHA256', 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-256-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.new('SHA256')

    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-256-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.new('SHA256')

    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

## `X509` Certificates¶ ↑

### Creating a Certificate¶ ↑

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

    key = OpenSSL::PKey::RSA.new 2048
    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.new('SHA1')

    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
    password = 'my secure password goes here'

    cipher = 'aes-256-cbc'

    open 'ca_key.pem', 'w', 0400 do |io|
      io.write ca_key.private_to_pem(cipher, password)
    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.new('SHA1')

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.new('SHA1')

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.new('SHA1')

    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 = ssl_connection.gets

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

      ssl_connection.puts "I got #{data.dump}"
      ssl_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.

Note that SSLSocket#close doesn’t close the underlying socket by default. `Set` SSLSocket#sync_close to true if you want.

    require 'socket'

    tcp_socket = TCPSocket.new 'localhost', 5000
    ssl_client = OpenSSL::SSL::SSLSocket.new tcp_socket, context
    ssl_client.sync_close = true
    ssl_client.connect

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

    ssl_client.close # shutdown the TLS connection and close tcp_socket

### 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_socket = TCPSocket.new 'localhost', 5000
    ssl_client = OpenSSL::SSL::SSLSocket.new tcp_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

LIBRESSL_VERSION_NUMBER

  Version number of LibreSSL the ruby `OpenSSL` extension was built with (base 16). The format is `0xMNNFF00f (major minor fix 00 status)`. This constant is only defined in LibreSSL cases.

  See also the man page `LIBRESSL_VERSION_NUMBER`(3).

OPENSSL_FIPS

  Boolean indicating whether `OpenSSL` is FIPS-capable or not

OPENSSL_LIBRARY_VERSION
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). The formats are below.

  `OpenSSL` 3

    `0xMNN00PP0 (major minor 00 patch 0)`

  `OpenSSL` before 3

    `0xMNNFFPPS (major minor fix patch status)`

  LibreSSL

    `0x20000000 (fixed value)`

  See also the man page `OPENSSL_VERSION_NUMBER`(3).

VERSION

### Public Class Methods

Digest (name)
Source

    # File ext/openssl/lib/openssl/digest.rb, line 63
    def Digest(name)
      OpenSSL::Digest.const_get(name)
    end

Returns a `Digest` subclass by name

    require 'openssl'

    OpenSSL::Digest("MD5")
    # => OpenSSL::Digest::MD5

    Digest("Foo")
    # => NameError: wrong constant name Foo

debug → true | false
Source

    static VALUE
    ossl_debug_get(VALUE self)
    {
        return dOSSL;
    }

debug = boolean → boolean
Source

    static VALUE
    ossl_debug_set(VALUE self, VALUE val)
    {
        dOSSL = RTEST(val) ? Qtrue : Qfalse;

        return val;
    }

Turns on or off debug mode. With debug mode, all errors added to the `OpenSSL` error queue will be printed to stderr.

errors → [String...]
Source

    static VALUE
    ossl_get_errors(VALUE _)
    {
        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;
    }

See any remaining errors held in queue.

Any errors you see here are probably due to a bug in Ruby’s `OpenSSL` implementation.

fips_mode → true | false
Source

    static VALUE
    ossl_fips_mode_get(VALUE self)
    {

    #if OSSL_OPENSSL_PREREQ(3, 0, 0)
        VALUE enabled;
        enabled = EVP_default_properties_is_fips_enabled(NULL) ? Qtrue : Qfalse;
        return enabled;
    #elif defined(OPENSSL_FIPS)
        VALUE enabled;
        enabled = FIPS_mode() ? Qtrue : Qfalse;
        return enabled;
    #else
        return Qfalse;
    #endif
    }

fips_mode = boolean → boolean
Source

    static VALUE
    ossl_fips_mode_set(VALUE self, VALUE enabled)
    {
    #if OSSL_OPENSSL_PREREQ(3, 0, 0)
        if (RTEST(enabled)) {
            if (!EVP_default_properties_enable_fips(NULL, 1)) {
                ossl_raise(eOSSLError, "Turning on FIPS mode failed");
            }
        } else {
            if (!EVP_default_properties_enable_fips(NULL, 0)) {
                ossl_raise(eOSSLError, "Turning off FIPS mode failed");
            }
        }
        return enabled;
    #elif defined(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
    }

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

fixed_length_secure_compare(string, string) → boolean
Source

    static VALUE
    ossl_crypto_fixed_length_secure_compare(VALUE dummy, VALUE str1, VALUE str2)
    {
        const unsigned char *p1 = (const unsigned char *)StringValuePtr(str1);
        const unsigned char *p2 = (const unsigned char *)StringValuePtr(str2);
        long len1 = RSTRING_LEN(str1);
        long len2 = RSTRING_LEN(str2);

        if (len1 != len2) {
            ossl_raise(rb_eArgError, "inputs must be of equal length");
        }

        switch (CRYPTO_memcmp(p1, p2, len1)) {
            case 0: return Qtrue;
            default: return Qfalse;
        }
    }

Constant time memory comparison for fixed length strings, such as results of `HMAC` calculations.

Returns `true` if the strings are identical, `false` if they are of the same length but not identical. If the length is different, `ArgumentError` is raised.

secure_compare(string, string) → boolean
Source

    # File ext/openssl/lib/openssl.rb, line 33
    def self.secure_compare(a, b)
      hashed_a = OpenSSL::Digest.digest('SHA256', a)
      hashed_b = OpenSSL::Digest.digest('SHA256', b)
      OpenSSL.fixed_length_secure_compare(hashed_a, hashed_b) && a == b
    end

Constant time memory comparison. Inputs are hashed using SHA-256 to mask the length of the secret. Returns `true` if the strings are identical, `false` otherwise.

### Private Instance Methods

Digest (name)
Source

    # File ext/openssl/lib/openssl/digest.rb, line 63
    def Digest(name)
      OpenSSL::Digest.const_get(name)
    end

Returns a `Digest` subclass by name

    require 'openssl'

    OpenSSL::Digest("MD5")
    # => OpenSSL::Digest::MD5

    Digest("Foo")
    # => NameError: wrong constant name Foo