=head1 NAME

Digest::SHA256 - a module that implements the NIST SHA-256/384/512 hash.

=head1 SYNOPSIS

 use Digest::SHA256;

 $context = new Digest::SHA256::new($size);
 $context->reset();
 $context->add(LIST);
 $context->addfile(HANDLE);

 $digest = $context->digest();
 $string = $context->hexdigest();

 $digest = $context->hash($string);
 $string = $context->hexhash($string);

=head1 DESCRIPTION

The B<sha256> module allows you to use the NIST SHA 256/384/512 hash
algorithm.

A new sha256 context object is created with the B<new> operation
followed by a digest size which may be either 256, 384, or 512 bits.
Multiple simultaneous digest context can be  maintained if desired.
The context is updated with the B<add> operation which adds the
strings contained in the I<LIST> parameter.

The final message digest value is returned by the B<digest> operation
as a 32-, 48-, or 64-byte binary string. This operation delivers the
result of operations since the last B<new> or B<reset> operation. Once
the operation has been performed, the context must be B<reset> before
being used to calculate another digest value.

Several convenience methods are also provided. The B<addfile> operation
takes an open file-handle and reads it until end-of file in 8192-byte
blocks adding the contents to the context. The B<hexdigest> operation
calls B<digest> and returns the result as a printable string of
hexadecimal digits in eight-digit groups. The B<hash> operation
performs the complete series of steps: B<reset>, B<add>, B<digest> on
the supplied scalar value, and returns the result as a 32-, 48-, or
64-byte binary string. The B<hexhash> operation does the same thing,
but returns the result in the format of the B<hexdigest> operation.

=head1 AUTHOR

SHA-256/384/512 C code and Perl interface by Rafael R. Sevilla, based on
specification paper provided by NIST.

For more information on this algorithm see:

http://csrc.nist.gov/cryptval/shs.html

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