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This module provides instance methods for a digest implementation object to calculate message digest values.

Used to construct C classes (CUnion, CStruct, etc)

Fiddle::Importer#struct and Fiddle::Importer#union wrap this functionality in an easy-to-use manner.

Mixin methods for install and update options for Gem::Commands

Module that defines the default UserInteraction. Any class including this module will have access to the ui method that returns the default UI.

UserInteraction allows RubyGems to interact with the user through standard methods that can be replaced with more-specific UI methods for different displays.

Since UserInteraction dispatches to a concrete UI class you may need to reference other classes for specific behavior such as Gem::ConsoleUI or Gem::SilentUI.

Example:

class X
  include Gem::UserInteraction

  def get_answer
    n = ask("What is the meaning of life?")
  end
end

Raised when encoding is invalid.

Enumerator::Chain is a subclass of Enumerator, which represents a chain of enumerables that works as a single enumerator.

This type of objects can be created by Enumerable#chain and Enumerator#+.

Enumerator::ArithmeticSequence is a subclass of Enumerator, that is a representation of sequences of numbers with common difference. Instances of this class can be generated by the Range#step and Numeric#step methods.

The class can be used for slicing Array (see Array#slice) or custom collections.

Fiddle::Pointer is a class to handle C pointers

FIXME: This isn’t documented in Nutshell.

Since MonitorMixin.new_cond returns a ConditionVariable, and the example above calls while_wait and signal, this class should be documented.

This class is used as a return value from ObjectSpace::reachable_objects_from.

When ObjectSpace::reachable_objects_from returns an object with references to an internal object, an instance of this class is returned.

You can use the type method to check the type of the internal object.

OpenSSL::Digest allows you to compute message digests (sometimes interchangeably called “hashes”) of arbitrary data that are cryptographically secure, i.e. a Digest implements a secure one-way function.

One-way functions offer some useful properties. E.g. given two distinct inputs the probability that both yield the same output is highly unlikely. Combined with the fact that every message digest algorithm has a fixed-length output of just a few bytes, digests are often used to create unique identifiers for arbitrary data. A common example is the creation of a unique id for binary documents that are stored in a database.

Another useful characteristic of one-way functions (and thus the name) is that given a digest there is no indication about the original data that produced it, i.e. the only way to identify the original input is to “brute-force” through every possible combination of inputs.

These characteristics make one-way functions also ideal companions for public key signature algorithms: instead of signing an entire document, first a hash of the document is produced with a considerably faster message digest algorithm and only the few bytes of its output need to be signed using the slower public key algorithm. To validate the integrity of a signed document, it suffices to re-compute the hash and verify that it is equal to that in the signature.

You can get a list of all digest algorithms supported on your system by running this command in your terminal:

openssl list -digest-algorithms

Among the OpenSSL 1.1.1 supported message digest algorithms are:

• SHA224, SHA256, SHA384, SHA512, SHA512-224 and SHA512-256

• SHA3-224, SHA3-256, SHA3-384 and SHA3-512

• BLAKE2s256 and BLAKE2b512

Each of these algorithms can be instantiated using the name:

digest = OpenSSL::Digest.new('SHA256')

“Breaking” a message digest algorithm means defying its one-way function characteristics, i.e. producing a collision or finding a way to get to the original data by means that are more efficient than brute-forcing etc. Most of the supported digest algorithms can be considered broken in this sense, even the very popular MD5 and SHA1 algorithms. Should security be your highest concern, then you should probably rely on SHA224, SHA256, SHA384 or SHA512.

Hashing a file

data = File.binread('document')
sha256 = OpenSSL::Digest.new('SHA256')
digest = sha256.digest(data)

Hashing several pieces of data at once

data1 = File.binread('file1')
data2 = File.binread('file2')
data3 = File.binread('file3')
sha256 = OpenSSL::Digest.new('SHA256')
sha256 << data1
sha256 << data2
sha256 << data3
digest = sha256.digest

Reuse a Digest instance

data1 = File.binread('file1')
sha256 = OpenSSL::Digest.new('SHA256')
digest1 = sha256.digest(data1)

data2 = File.binread('file2')
sha256.reset
digest2 = sha256.digest(data2)

Subclasses ‘BadAlias` for backwards compatibility