Provided by: libbytes-random-secure-perl_0.28-1_all 
NAME
Bytes::Random::Secure - Perl extension to generate cryptographically-secure random bytes.
SYNOPSIS
use Bytes::Random::Secure qw(
random_bytes random_bytes_base64 random_bytes_hex
);
my $bytes = random_bytes(32); # A string of 32 random bytes.
my $bytes = random_string_from( 'abcde', 10 ); # 10 random a,b,c,d, and e's.
my $bytes_as_base64 = random_bytes_base64(57); # Base64 encoded rand bytes.
my $bytes_as_hex = random_bytes_hex(8); # Eight random bytes as hex digits.
my $bytes_as_quoted_printable = random_bytes_qp(100); # QP encoded bytes.
my $random = Bytes::Random::Secure->new(
Bits => 64,
NonBlocking => 1,
); # Seed with 64 bits, and use /dev/urandom (or other non-blocking).
my $bytes = $random->bytes(32); # A string of 32 random bytes.
my $long = $random->irand; # 32-bit random integer.
DESCRIPTION
Bytes::Random::Secure provides two interfaces for obtaining crypto-quality random bytes. The simple
interface is built around plain functions. For greater control over the Random Number Generator's
seeding, there is an Object Oriented interface that provides much more flexibility.
The "functions" interface provides functions that can be used any time you need a string of a specific
number of random bytes. The random bytes are available as simple strings, or as hex-digits, Quoted
Printable, or MIME Base64. There are equivalent methods available from the OO interface, plus a few
others.
This module can be a drop-in replacement for Bytes::Random, with the primary enhancement of using a
cryptographic-quality random number generator to create the random data. The "random_bytes" function
emulates the user interface of Bytes::Random's function by the same name. But with Bytes::Random::Secure
the random number generator comes from Math::Random::ISAAC, and is suitable for cryptographic purposes.
The harder problem to solve is how to seed the generator. This module uses Crypt::Random::Seed to
generate the initial seeds for Math::Random::ISAAC.
In addition to providing "random_bytes()", this module also provides several functions not found in
Bytes::Random: "random_string_from", "random_bytes_base64()", "random_bytes_hex", and "random_bytes_qp".
And finally, for those who need finer control over how Crypt::Random::Seed generates its seed, there is
an object oriented interface with a constructor that facilitates configuring the seeding process, while
providing methods that do everything the "functions" interface can do (truth be told, the functions
interface is just a thin wrapper around the OO version, with some sane defaults selected). The OO
interface also provides an "irand" method, not available through the functions interface.
RATIONALE
There are many uses for cryptographic quality randomness. This module aims to provide a generalized tool
that can fit into many applications while providing a minimal dependency chain, and a user interface that
is simple. You're free to come up with your own use-cases, but there are several obvious ones:
• Creating temporary passphrases ("random_string_from()").
• Generating per-account random salt to be hashed along with passphrases (and stored alongside them) to
prevent rainbow table attacks.
• Generating a secret that can be hashed along with a cookie's session content to prevent cookie
forgeries.
• Building raw cryptographic-quality pseudo-random data sets for testing or sampling.
• Feeding secure key-gen utilities.
Why use this module? This module employs several well-designed CPAN tools to first generate a strong
random seed, and then to instantiate a high quality random number generator based on the seed. The code
in this module really just glues together the building blocks. However, it has taken a good deal of
research to come up with what I feel is a strong tool-chain that isn't going to fall back to a weak state
on some systems. The interface is designed with simplicity in mind, to minimize the potential for
misconfiguration.
EXPORTS
By default "random_bytes" is the only function exported. Optionally "random_string_from",
"random_bytes_base64", "random_bytes_hex", and "random_bytes_qp" may be exported.
FUNCTIONS
The functions interface seeds the ISAAC generator on first use with a 256 bit seed that uses
Crypt::Random::Seed's default configuration as a strong random seed source.
random_bytes
my $random_bytes = random_bytes( 512 );
Returns a string containing as many random bytes as requested. Obviously the string isn't useful for
display, as it can contain any byte value from 0 through 255.
The parameter is a byte-count, and must be an integer greater or equal to zero.
random_string_from
my $random_bytes = random_string_from( $bag, $length );
my $random_bytes = random_string_from( 'abc', 50 );
$bag is a string of characters from which "random_string_from" may choose in building a random string.
We call it a 'bag', because it's permissible to have repeated chars in the bag (if not, we could call it
a set). Repeated digits get more weight. For example, "random_string_from( 'aab', 1 )" would have a
66.67% chance of returning an 'a', and a 33.33% chance of returning a 'b'. For unweighted distribution,
ensure there are no duplicates in $bag.
This isn't a "draw and discard", or a permutation algorithm; each character selected is independent of
previous or subsequent selections; duplicate selections are possible by design.
Return value is a string of size $length, of characters chosen at random from the 'bag' string.
It is perfectly legal to pass a Unicode string as the "bag", and in that case, the yield will include
Unicode characters selected from those passed in via the bag string.
This function is useful for random string generation such as temporary random passwords.
random_bytes_base64
my $random_bytes_b64 = random_bytes_base64( $num_bytes );
my $random_bytes_b64_formatted = random_bytes_base64( $num_bytes, $eol );
Returns a MIME Base64 encoding of a string of $number_of_bytes random bytes. Note, it should be obvious,
but is worth mentioning that a base64 encoding of base256 data requires more digits to represent the
bytes requested. The actual number of digits required, including padding is "4(n/3)". Furthermore, the
Base64 standard is to add padding to the end of any string for which "length % 57" is a non-zero value.
If an $eol is specified, the character(s) specified will be used as line delimiters after every 76th
character. The default is "qq{\n}". If you wish to eliminate line-break insertions, specify an empty
string: "q{}".
random_bytes_hex
my $random_bytes_as_hex = random_bytes_hex( $num_bytes );
Returns a string of hex digits representing the string of $number_of_bytes random bytes.
It's worth mentioning that a hex (base16) representation of base256 data requires two digits for every
byte requested. So "length( random_bytes_hex( 16 ) )" will return 32, as it takes 32 hex digits to
represent 16 bytes. Simple stuff, but better to mention it now than forget and set a database field
that's too narrow.
random_bytes_qp
my $random_bytes_qp = random_bytes_qp( $num_bytes );
my $random_bytes_qp_formatted = random_bytes_qp( $num_bytes, $eol );
Produces a string of $num_bytes random bytes, using MIME Quoted Printable encoding (as produced by
MIME::QuotedPrint's "encode_qp" function. The default configuration uses "\n" as a line break after
every 76 characters, and the "binmode" setting is used to guarantee a lossless round trip. If no line
break is wanted, pass an empty string as $eol.
METHODS
The Object Oriented interface provides methods that mirror the "functions" interface. However, the OO
interface offers the advantage that the user can control how many bits of entropy are used in seeding,
and even how Crypt::Random::Seed is configured.
new
my $random = Bytes::Random::Secure->new( Bits => 512 );
my $bytes = $random->bytes( 32 );
The constructor is used to specify how the ISAAC generator is seeded. Future versions may also allow for
alternate CSPRNGs to be selected. If no parameters are passed the default configuration specifies 256
bits for the seed. The rest of the default configuration accepts the Crypt::Random::Seed defaults, which
favor the strongest operating system provided entropy source, which in many cases may be "blocking".
CONSTRUCTOR PARAMETERS
Bits
my $random = Bytes::Random::Secure->new( Bits => 128 );
The "Bits" parameter specifies how many bits (rounded up to nearest multiple of 32) will be used in
seeding the ISAAC random number generator. The default is 256 bits of entropy. But in some cases it may
not be necessary, or even wise to pull so many bits of entropy out of "/dev/random" (a blocking source).
Any value between 64 and 8192 will be accepted. If an out-of-range value is specified, or a value that is
not a multiple of 32, a warning will be generated and the parameter will be rounded up to the nearest
multiple of 32 within the range of 64 through 8192 bits. So if 16384 is specified, you will get 8192.
If 33 is specified, you will get 64.
Note: In the Perlish spirit of "no arbitrary limits", the maximum number of bits this module accepts is
8192, which is the maximum number that ISAAC can utilize. But just because you can specify a seed of
8192 bits doesn't mean you ought to, much less need to. And if you do, you probably want to use the
"NonBlocking" option, discussed below. 8192 bits is a lot to ask from a blocking source such as
"/dev/random", and really anything beyond 512 bits in the seed is probably wasteful.
PRNG
Reserved for future use. Eventually the user will be able to select other RNGs aside from
Math::Random::ISAAC.
Unique
Reserved for future use.
Other Crypt::Random::Seed Configuration Parameters
For additional seeding control, refer to the POD for Crypt::Random::Seed. By supplying a
Crypt::Random::Seed parameter to Bytes::Random::Secure's constructor, it will be passed through to
Crypt::Random::Seed. For example:
my $random = Bytes::Random::Secure->new( NonBlocking => 1, Bits => 64 );
In this example, "Bits" is used internally, while "NonBlocking" is passed through to Crypt::Random::Seed.
bytes
my $random_bytes = $random->bytes(1024);
This works just like the "random_bytes" function.
string_from
my $random_string = $random->string_from( 'abcdefg', 10 );
Just like "random_string_from": Returns a string of random octets selected from the "Bag" string (in this
case ten octets from 'abcdefg').
bytes_hex
my $random_hex = $random->bytes_hex(12);
Identical in function to "random_bytes_hex".
bytes_base64
my $random_base64 = $random->bytes_base64( 32, EOL => "\n" );
Identical in function to "random_bytes_base64".
bytes_qp
my $random_qp = $random->bytes_qp( 80 );
You guessed it: Identical in function to "random_bytes_qp".
irand
my $unsigned_long = $random->irand;
Returns a random 32-bit unsigned integer. The value will satisfy "0 <= x <= 2**32-1". This
functionality is only available through the OO interface.
CONFIGURATION
Bytes::Random::Secure's interface tries to keep it simple. There is generally nothing to configure.
This design, eliminates much of the potential for diminishing the quality of the random byte stream
through misconfiguration. The ISAAC algorithm is used as our factory, seeded with a strong source.
There may be times when the default seed characteristics carry too heavy a burden on system resources.
The default seed for the functions interface is 256 bits of entropy taken from /dev/random (a blocking
source on many systems), or via API calls on Windows. The default seed size for the OO interface is also
256 bits. If /dev/random should become depleted at the time that this module attempts to seed the ISAAC
generator, there could be delay while additional system entropy is generated. If this is a problem, it
is possible to override the default seeding characteristics using the OO interface instead of the
functions interface. However, under most circumstances, this capability may be safely ignored.
Beginning with Bytes::Random::Secure version 0.20, Crypt::Random::Seed provides our strong seed
(previously it was Crypt::Random::Source). This module gives us excellent "strong source" failsafe
behavior, while keeping the non-core dependencies to a bare minimum. Best of all, it performs well
across a wide variety of platforms, and is compatible with Perl versions back through 5.6.0.
And as mentioned earlier in this document, there may be circumstances where the performance of the
operating system's strong random source is prohibitive from using the module's default seeding
configuration. Use the OO interface instead, and read the documentation for Crypt::Random::Seed to learn
what options are available.
Prior to version 0.20, a heavy dependency chain was required for reliably and securely seeding the ISAAC
generator. Earlier versions required Crypt::Random::Source, which in turn required Any::Moose. Thanks
to Dana Jacobsen's new Crypt::Random::Seed module, this situation has been resolved. So if you're
looking for a secure random bytes solution that "just works" portably, and on Perl versions as far back
as 5.6.0, you've come to the right place. Users of older versions of this module are encouraged to
update to version 0.20 or higher to benefit from the improved user interface and lighter dependency
chain.
OPTIONAL (RECOMMENDED) DEPENDENCY
If performance is a consideration, you may also install Math::Random::ISAAC::XS. Bytes::Random::Secure's
random number generator uses Math::Random::ISAAC. That module implements the ISAAC algorithm in pure
Perl. However, if you install Math::Random::ISAAC::XS, you get the same algorithm implemented in C/XS,
which will provide better performance. If you need to produce your random bytes more quickly, simply
installing Math::Random::ISAAC::XS will result in it automatically being used, and a pretty good
performance improvement will coincide.
CAVEATS
FORK AND THREAD SAFETY
When programming for parallel computation, avoid the "functions" interface do use the Object Oriented
interface, and create a unique "Bytes::Random::Secure" object within each process or thread.
Bytes::Random::Secure uses a CSPRNG, and sharing the same RNG between threads or processes will share the
same seed and the same starting point. This is probably not what one would want to do. By instantiating
the B::R::S object after forking or creating threads, a unique randomness stream will be created per
thread or process.
STRONG RANDOMNESS
It's easy to generate weak pseudo-random bytes. It's also easy to think you're generating strong pseudo-
random bytes when really you're not. And it's hard to test for pseudo-random cryptographic acceptable
quality. There are many high quality random number generators that are suitable for statistical
purposes, but not necessarily up to the rigors of cryptographic use.
Assuring strong (ie, secure) random bytes in a way that works across a wide variety of platforms is also
challenging. A primary goal for this module is to provide cryptographically secure pseudo-random bytes.
A secondary goal is to provide a simple user experience (thus reducing the propensity for getting it
wrong). A tertiary goal is to minimize the dependencies required to achieve the primary and secondary
goals, to the extent that is practical.
ISAAC
The ISAAC algorithm is considered to be a cryptographically strong pseudo-random number generator. There
are 1.0e2466 initial states. The best known attack for discovering initial state would theoretically
take a complexity of approximately 4.67e1240, which has no practical impact on ISAAC's security. Cycles
are guaranteed to have a minimum length of 2**40, with an average cycle of 2**8295. Because there is no
practical attack capable of discovering initial state, and because the average cycle is so long, it's
generally unnecessary to re-seed a running application. The results are uniformly distributed, unbiased,
and unpredictable unless the seed is known.
To confirm the quality of the CSPRNG, this module's test suite implements the FIPS-140-1
<http://csrc.nist.gov/publications/fips/fips1401.htm> tests for strong random number generators. See the
comments in "t/27-fips140-1.t" for details.
DEPENDENCIES
To keep the dependencies as light as possible this module uses some ideas from Math::Random::Secure.
That module is an excellent resource, but implements a broader range of functionality than is needed
here. So we just borrowed from it.
The primary source of random data in this module comes from the excellent Math::Random::ISAAC. To be
useful and secure, even Math::Random::ISAAC needs a cryptographically sound seed, which we derive from
Crypt::Random::Seed. There are no known weaknesses in the ISAAC algorithm. And Crypt::Random::Seed does
a very good job of preventing fall-back to weak seed sources.
This module requires Perl 5.6 or newer. The module also uses a number of core modules, some of which
require newer versions than those contemporary with 5.6. Unicode support in "random_string_from" is best
with Perl 5.8.9 or newer. See the INSTALLATION section in this document for details.
If Test::Warn is installed, test coverage is 100%. For those who don't want to bother installing
Test::Warn, you can just take our word for it. It's an optional installation dependency.
BLOCKING ENTROPY SOURCE
It is possible (and has been seen in testing) that the system's random entropy source might not have
enough entropy in reserve to generate the seed requested by this module without blocking. If you suspect
that you're a victim of blocking from reads on "/dev/random", one option is to manipulate the random seed
configuration by using the object oriented interface.
This module seeds as lazily as possible so that using the module, and even instantiating a
Bytes::Random::Secure object will not trigger reads from "/dev/random". Only the first time the object
is used to deliver random bytes will the RNG be seeded. Long-running scripts may prefer to force early
seeding as close to start-up time as possible, rather than allowing it to happen later in a program's
run-time. This can be achieved simply by invoking any of the functions or methods that return a random
byte. As soon as a random byte is requested for the first time, the CSPRNG will be seeded.
UNICODE SUPPORT
The "random_string_from" function, and "string_from" method permit the user to pass a "bag" (or source)
string containing Unicode characters. For any modern Perl version, this will work just as you would
hope. But some versions of Perl older than 5.8.9 exhibited varying degrees of bugginess in their
handling of Unicode. If you're depending on the Unicode features of this module while using Perl
versions older than 5.8.9 be sure to test thoroughly, and don't be surprised when the outcome isn't as
expected. ...this is to be expected. Upgrade.
No other functions or methods in this module get anywhere near Perl's Unicode features. So as long as
you're not passing Unicode source strings to "random_string_from", you have nothing to worry about, even
if you're using Perl 5.6.0.
MODULO BIAS
Care is taken so that there is no modulo bias in the randomness returned either by "random_bytes" or its
siblings, nor by "random_string_from". As a matter if fact, this is exactly why the "random_string_from"
function is useful. However, the algorithm to eliminate modulo bias can impact the performance of the
"random_string_from" function. Any time the length of the bag string is significantly less than the
nearest greater or equal factor of 2**32, performance will degrade. Unfortunately there is no known
algorithm that improves upon this situation. Fortunately, for sanely sized strings, it's a minor issue.
To put it in perspective, even in the case of passing a "bag" string of length 2**31 (which is huge), the
expected time to return random bytes will only double. Given that the entire Unicode range is just over
a million possible code-points, it seems unlikely that the normal use case would ever have to be
concerned with the performance of the "random_string_from" function.
INSTALLATION
This module should install without any fuss on modern versions of Perl. For older Perl versions
(particularly 5.6 and early 5.8.x's), it may be necessary to update your CPAN installer to a more modern
version before installing this this module.
Another alternative for those with old Perl versions who don't want to update their CPAN installer (You
must know you're crazy, right?): Review "Makefile.PL" and assure that you've got the dependencies listed
under "PREREQ_PM" and "BUILD_REQUIRES", in at least the minimum versions specified. Then proceed as
usual.
This module only has two non-Core dependencies. But it does expect that some of the Core dependencies
are newer than those supplied with 5.6 or early 5.8's. If you keep your CPAN installer up-to-date, you
shouldn't have to think about this, as it will usually just "do the right thing", pulling in newer
dependency versions as directed by the module's META files.
Test coverage for Bytes::Random::Secure is 100% (per Devel::Cover) on any system that has Test::Warn
installed. But to keep the module light-weight, Test::Warn is not dragged in by default at installation
time.
AUTHOR
David Oswald "<davido [at] cpan (dot) org>"
BUGS
Please report any bugs or feature requests to "bug-bytes-random-secure at rt.cpan.org", or through the
web interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Bytes-Random-Secure>. I will be
notified, and then you'll automatically be notified of progress on your bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc Bytes::Random::Secure
You can also look for information at:
• Github Repo: <https://github.com/daoswald/Bytes-Random-Secure>
• RT: CPAN's request tracker (report bugs here)
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Bytes-Random-Secure>
• AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/Bytes-Random-Secure>
• CPAN Ratings
<http://cpanratings.perl.org/d/Bytes-Random-Secure>
• Search CPAN
<http://search.cpan.org/dist/Bytes-Random-Secure/>
ACKNOWLEDGEMENTS
Dana Jacobsen ( <dana@acm.org> ) for his work that led to Crypt::Random::Seed, thereby significantly
reducing the dependencies while improving the portability and backward compatibility of this module.
Also for providing a patch to this module that greatly improved the performance of "random_bytes".
Dana Jacosen also provided extensive input, code reviews, and testing that helped to guide the direction
this module has taken. The code for the FIPS-140-1 tests was taken directly from Crypt::Random::TESHA2.
Thanks!
Bytes::Random for implementing a nice, simple interface that this module patterns itself after.
LICENSE AND COPYRIGHT
Copyright 2012 David Oswald.
This program is free software; you can redistribute it and/or modify it under the terms of either: the
GNU General Public License as published by the Free Software Foundation; or the Artistic License.
See http://dev.perl.org/licenses/ for more information.