What's the size of a HMACSHA2 hash in Crypt::PBKDF2 in Perl?

Question

I want to store password hashes in a database. Hashes will be generated with

my $PBKDF2 = Crypt::PBKDF2->new(
    hash_class => 'HMACSHA2',
    hash_args => {
        sha_size => 512,
    },
    iterations => 10000,
    salt_len => 10,
);

In the Pod of Crypt::PBKDF2 I find:

The default size (in bytes, not bits) of the output hash. If a value isn't provided, the output size depends on the hash_class / hasher selected, and will equal the output size of the backend hash (e.g. 20 bytes for HMACSHA1).

But what actually IS the default output size?

Answer 1

32 bytes

You can find this information in the source code of Crypt::PBKDF2::Hash::HMACSHA2. The code defining the default size is:

has 'sha_size' => (
  is => 'ro',
  isa => Type::Tiny->new(
    name => 'SHASize',
    parent => Enum[qw( 224 256 384 512 )],
    display_name => 'valid number of bits for SHA-2',
  ),
  default => 256,
);

The function used to return the size divides sha_size by 8:

sub hash_len {
  my $self = shift;
  return $self->sha_size() / 8;
}

Thus returning 256/8 = 32 by default.