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Raised when attempting to divide an integer by 0.

42 / 0   #=> ZeroDivisionError: divided by 0

Note that only division by an exact 0 will raise the exception:

42 /  0.0   #=> Float::INFINITY
42 / -0.0   #=> -Float::INFINITY
0  /  0.0   #=> NaN

ConditionVariable objects augment class Mutex. Using condition variables, it is possible to suspend while in the middle of a critical section until a resource becomes available.

Example:

mutex = Mutex.new
resource = ConditionVariable.new

a = Thread.new {
   mutex.synchronize {
     # Thread 'a' now needs the resource
     resource.wait(mutex)
     # 'a' can now have the resource
   }
}

b = Thread.new {
   mutex.synchronize {
     # Thread 'b' has finished using the resource
     resource.signal
   }
}

This module provides a framework for message digest libraries.

You may want to look at OpenSSL::Digest as it supports more algorithms.

A cryptographic hash function is a procedure that takes data and returns a fixed bit string: the hash value, also known as digest. Hash functions are also called one-way functions, it is easy to compute a digest from a message, but it is infeasible to generate a message from a digest.

Examples

require 'digest'

# Compute a complete digest
Digest::SHA256.digest 'message'       #=> "\xABS\n\x13\xE4Y..."

sha256 = Digest::SHA256.new
sha256.digest 'message'               #=> "\xABS\n\x13\xE4Y..."

# Other encoding formats
Digest::SHA256.hexdigest 'message'    #=> "ab530a13e459..."
Digest::SHA256.base64digest 'message' #=> "q1MKE+RZFJgr..."

# Compute digest by chunks
md5 = Digest::MD5.new
md5.update 'message1'
md5 << 'message2'                     # << is an alias for update

md5.hexdigest                         #=> "94af09c09bb9..."

# Compute digest for a file
sha256 = Digest::SHA256.file 'testfile'
sha256.hexdigest

Additionally digests can be encoded in “bubble babble” format as a sequence of consonants and vowels which is more recognizable and comparable than a hexadecimal digest.

require 'digest/bubblebabble'

Digest::SHA256.bubblebabble 'message' #=> "xopoh-fedac-fenyh-..."

See the bubble babble specification at web.mit.edu/kenta/www/one/bubblebabble/spec/jrtrjwzi/draft-huima-01.txt.

Digest algorithms

Different digest algorithms (or hash functions) are available:

MD5

See RFC 1321 The MD5 Message-Digest Algorithm

RIPEMD-160

As Digest::RMD160. See homes.esat.kuleuven.be/~bosselae/ripemd160.html.

SHA1

See FIPS 180 Secure Hash Standard.

SHA2 family

See FIPS 180 Secure Hash Standard which defines the following algorithms:

• SHA512

• SHA384

• SHA256

The latest versions of the FIPS publications can be found here: csrc.nist.gov/publications/PubsFIPS.html.

306 Switch Proxy - no longer unused

418 I’m a teapot - RFC 2324; a joke RFC 420 Enhance Your Calm - Twitter

Raised on redirection, only occurs when redirect option for HTTP is false.

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.

Among the supported message digest algorithms are:

• SHA, SHA1, SHA224, SHA256, SHA384 and SHA512

• MD2, MD4, MDC2 and MD5

• RIPEMD160

• DSS, DSS1 (Pseudo algorithms to be used for DSA signatures. DSS is equal to SHA and DSS1 is equal to SHA1)

For each of these algorithms, there is a sub-class of Digest that can be instantiated as simply as e.g.

digest = OpenSSL::Digest::SHA1.new

Mapping between Digest class and sn/ln

The sn (short names) and ln (long names) are defined in <openssl/object.h> and <openssl/obj_mac.h>. They are textual representations of ASN.1 OBJECT IDENTIFIERs. Each supported digest algorithm has an OBJECT IDENTIFIER associated to it and those again have short/long names assigned to them. E.g. the OBJECT IDENTIFIER for SHA-1 is 1.3.14.3.2.26 and its sn is “SHA1” and its ln is “sha1”.

MD2

• sn: MD2

• ln: md2

MD4

• sn: MD4

• ln: md4

MD5

• sn: MD5

• ln: md5

SHA

• sn: SHA

• ln: SHA

SHA-1

• sn: SHA1

• ln: sha1

SHA-224

• sn: SHA224

• ln: sha224

SHA-256

• sn: SHA256

• ln: sha256

SHA-384

• sn: SHA384

• ln: sha384

SHA-512

• sn: SHA512

• ln: sha512

“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.read('document')
sha256 = OpenSSL::Digest::SHA256.new
digest = sha256.digest(data)

Hashing several pieces of data at once

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

Reuse a Digest instance

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

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

Subclass of Zlib::Error

When zlib returns a Z_NEED_DICT if a preset dictionary is needed at this point.

Used by Zlib::Inflate.inflate and Zlib.inflate

Exception raised when there is an invalid encoding detected

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.

425 Unordered Collection - existed only in draft

An implementation of PseudoPrimeGenerator which uses a prime table generated by trial division.