James Aitken (PAUSE Custodial Account) > Dancer-Plugin-Passphrase > Dancer::Plugin::Passphrase

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Module Version: 2.0.1   Source   Latest Release: Dancer-Plugin-Passphrase-2.0.3

NAME ^

Dancer::Plugin::Passphrase - Passphrases and Passwords as objects for Dancer

SYNOPSIS ^

This plugin manages the hashing of passwords for Dancer apps, allowing developers to follow cryptography best practices without having to become a cryptography expert.

It uses the bcrypt algorithm as the default, while also supporting any hashing function provided by Digest

USAGE ^

    package MyWebService;
    use Dancer ':syntax';
    use Dancer::Plugin::Passphrase;

    post '/login' => sub {
        my $phrase = passphrase( param('my password') )->generate;

        # $phrase is now an object that contains RFC 2307 representation
        # of the hashed passphrase, along with the salt, and other metadata
        
        # You should store $phrase->rfc2307() for use later
    };

    get '/protected' => sub {
        # Retrieve $stored_rfc_2307_string, like we created above.
        # IT MUST be a valid RFC 2307 string

        if ( passphrase( param('my password') )->matches( $stored_rfc_2307 ) ) {
            # Passphrase matches!
        }
    };

    get '/generate_new_password' => sub {
        return passphrase->generate_random;
    };

KEYWORDS ^

passphrase

Given a plaintext password, it returns a Dancer::Plugin::Passphrase object that you can generate a new hash from, or match against a stored hash.

MAIN METHODS ^

generate

Generates an RFC 2307 representation of the hashed passphrase that is suitable for storage in a database.

    my $pass = passphrase('my passphrase')->generate;

You should store $phrase-rfc_2307()> in your database. For convenience the object will automagically return the RFC 2307 representation when no method is called on it.

Accepts a hashref of options to specify what kind of hash should be generated. All options settable in the config file are valid.

If you specify only the algorithm, the default settings for that algorithm will be used.

A cryptographically random salt is used if salt is not defined. Only if you specify the empty string will an empty salt be used This is not recommended, and should only be used to upgrade old insecure hashes

    my $phrase = passphrase('my password')->generate({
        algorithm  => '',   # What algorithm is used to generate the hash
        cost       => '',   # Cost / Work Factor if using bcrypt
        salt       => '',   # Manually specify salt if using a salted digest
    });

matches

Matches a plaintext password against a stored hash. Returns 1 if the hash of the password matches the stored hash. Returns undef if they don't match or if there was an error Fail-Secure, rather than Fail-Safe.

    passphrase('my password')->matches($stored_rfc_2307_string);

$stored_rfc_2307_string MUST be a valid RFC 2307 string, as created by generate()

An RFC 2307 string is made up of a scheme identifier, followed by a base64 encoded string. The base64 encoded string should contain the password hash and the salt concatenated together - in that order.

    '{'.$scheme.'}'.encode_base64($hash . $salt, '');

Where $scheme can be any of the following and their unsalted variants, which have the leading S removed. CRYPT will be Bcrypt.

    SMD5 SSHA SSHA224 SSHA256 SSHA384 SSHA512 CRYPT

A complete RFC2307 string looks like this:

    {SSHA}K3LAbIjRL5CpLzOlm3/HzS3qt/hUaGVTYWx0

This is the format created by generate()

generate_random

Generates and returns any number of cryptographically random characters from the url-safe base64 charater set.

    my $rand_pass = passphrase->generate_random;

The passwords generated are suitable for use as temporary passwords or one-time authentication tokens.

You can configure the length and the character set used by passing a hashref of options.

    my $rand_pass = passphrase->generate_random({
        length  => 32,
        charset => ['a'..'z', 'A'..'Z'],
    });

ADDITIONAL METHODS ^

The methods are only applicable once you have called generate

    passphrase( 'my password' )->generate->rfc2307; # CORRECT

    passphrase( 'my password' )->rfc2307;           # INCORRECT, Returns undef

rfc2307

Returns the rfc2307 representation from a Dancer::Plugin::Passphrase object.

    passphrase('my password')->generate->rfc2307;

scheme

Returns the scheme name from a Dancer::Plugin::Passphrase object.

This is the scheme name as used in the RFC 2307 representation

    passphrase('my password')->generate->scheme;

The scheme name can be any of the following, and will always be capitalized

    SMD5  SSHA  SSHA224  SSHA256  SSHA384  SSHA512  CRYPT
    MD5   SHA   SHA224   SHA256   SHA384   SHA512

algorithm

Returns the algorithm name from a Dancer::Plugin::Passphrase object.

The algorithm name can be anything that is accepted by Digest-new($alg)> This includes any modules in the Digest:: Namespace

    passphrase('my password')->generate->algorithm;

cost

Returns the bcrypt cost from a Dancer::Plugin::Passphrase object. Only works when using the bcrypt algorithm, returns undef for other algorithms

    passphrase('my password')->generate->cost;

salt_raw

Returns the raw salt from a Dancer::Plugin::Passphrase object.

    passphrase('my password')->generate->salt_raw;

Can be defined, but false - The empty string is technically a valid salt.

Returns undef if there is no salt.

hash_raw

Returns the raw hash from a Dancer::Plugin::Passphrase object.

    passphrase('my password')->generate->hash_raw;

salt_hex

Returns the hex-encoded salt from a Dancer::Plugin::Passphrase object.

Can be defined, but false - The empty string is technically a valid salt. Returns undef if there is no salt.

    passphrase('my password')->generate->salt_hex;

hash_hex

Returns the hex-encoded hash from a Dancer::Plugin::Passphrase object.

    passphrase('my password')->generate->hash_hex;

salt_base64

Returns the base64 encoded salt from a Dancer::Plugin::Passphrase object.

Can be defined, but false - The empty string is technically a valid salt. Returns undef if there is no salt.

    passphrase('my password')->generate->salt_base64;

hash_base64

Returns the base64 encoded hash from a Dancer::Plugin::Passphrase object.

    passphrase('my password')->generate->hash_base64;

plaintext

Returns the plaintext password as originally supplied to the passphrase keyword.

    passphrase('my password')->generate->plaintext;

MORE INFORMATION ^

Purpose

The aim of this module is to help you store new passwords in a secure manner, whilst still being able to verify and upgrade older passwords.

Cryptography is a vast and complex field. Many people try to roll their own methods for securing user data, but succeed only in coming up with a system that has little real security.

This plugin provides a simple way of managing that complexity, allowing developers to follow crypto best practice without having to become an expert.

Rationale

The module defaults to hashing passwords using the bcrypt algorithm, returning them in RFC 2307 format.

RFC 2307 describes an encoding system for passphrase hashes, as used in the "userPassword" attribute in LDAP databases. It encodes hashes as ASCII text, and supports several passphrase schemes by starting the encoding with an alphanumeric scheme identifier enclosed in braces.

RFC 2307 only specifies the MD5, and SHA schemes - however in real-world usage, schemes that are salted are widely supported, and are thus provided by this module.

Bcrypt is an adaptive hashing algorithm that is designed to resist brute force attacks by including a cost (aka work factor). This cost increases the computational effort it takes to compute the hash.

SHA and MD5 are designed to be fast, and modern machines compute a billion hashes a second. With computers getting faster every day, brute forcing SHA hashes is a very real problem that cannot be easily solved.

Increasing the cost of generating a bcrypt hash is a trivial way to make brute forcing ineffective. With a low cost setting, bcrypt is just as secure as a more traditional SHA+salt scheme, and just as fast. Increasing the cost as computers become more powerful keeps you one step ahead

For a more detailed description of why bcrypt is preferred, see this article: http://codahale.com/how-to-safely-store-a-password/

Configuration

In your applications config file, you can set the default hashing algorithm, and the default settings for every supported algorithm. Calls to generate() will use the default settings for that algorithm specified in here.

You can override these defaults when you call generate().

If you do no configuration at all, the default is to bcrypt with a cost of 4, and a strong psuedo-random salt.

    plugins:
        Passphrase:
            default: Bcrypt

            Bcrypt:
                cost: 8

Storage in a database

You should be storing the RFC 2307 string in your database, it's the easiest way to use this module. You could store the raw_salt, raw_hash, and scheme separately, but this strongly discouraged. RFC 2307 strings are specifically designed for storing hashed passwords, and should be used wherever possible.

The length of the string produced by generate() can vary dependent on your settings. Below is a table of the lengths generated using default settings.

You will need to make sure your database columns are at least this long. If the string gets truncated, the password can never be validated.

    ALGORITHM   LENGTH  EXAMPLE RFC 2307 STRING
    
    Bcrypt      68      {CRYPT}$2a$04$MjkMhQxasFQod1qq56DXCOvWu6YTWk9X.EZGnmSSIbbtyEBIAixbS
    SHA-512     118     {SSHA512}lZG4dZ5EU6dPEbJ1kBPPzEcupFloFSIJjiXCwMVxJXOy/x5qhBA5XH8FiUWj7u59onQxa97xYdqje/fwY5TDUcW1Urplf3KHMo9NO8KO47o=
    SHA-384     98      {SSHA384}SqZF5YYyk4NdjIM8YgQVfRieXDxNG0dKH4XBcM40Eblm+ribCzdyf0JV7i2xJvVHZsFSQNcuZPKtiTMzDyOU+w==
    SHA-256     74      {SSHA256}xsJHNzPlNCpOZ41OkTfQOU35ZY+nRyZFaM8lHg5U2pc0xT3DKNlGW2UTY0NPYsxU
    SHA-224     70      {SSHA224}FTHNkvKOdyX1d6f45iKLVxpaXZiHel8pfilUT1dIZ5u+WIUyhDGxLnx72X0=
    SHA-1       55      {SSHA}Qsaao/Xi/bYTRMQnpHuD3y5nj02wbdcw5Cek2y2nLs3pIlPh
    MD5         51      {SMD5}bgfLiUQWgzUm36+nBhFx62bi0xdwTp+UpEeNKDxSLfM=

Common Mistakes

Common mistakes people make when creating their own solution. If any of these seem familiar, you should probably be using this module

Passwords are stored as plain text for a reason

There is never a valid reason to store a password as plain text. Passwords should be reset and not emailed to customers when they forget. Support people should be able to login as a user without knowing the users password. No-one except the user should know the password - that is the point of authentication.

No-one will ever guess our super secret algorithm!

Unless you're a cryptography expert with many years spent studying super-complex maths, your algorithm is almost certainly not as secure as you think. Just because it's hard for you to break doesn't mean it's difficult for a computer.

Our application-wide salt is "Sup3r_S3cret_L0ng_Word" - No-one will ever guess that.

This is common misunderstanding of what a salt is meant to do. The purpose of a salt is to make sure the same password doesn't always generate the same hash. A fresh salt needs to be created each time you hash a password. It isn't meant to be a secret key.

We generate our random salt using rand.

rand isn't actually random, it's a non-unform pseudo-random number generator, and not suitable for cryptographic applications. Whilst this module also defaults to a PRNG, it is better than the one provided by rand. Using a true RNG is a config option away, but is not the default as it it could potentially block output if the system does not have enough entropy to generate a truly random number

We use md5(pass.salt), and the salt is from /dev/random

MD5 has been broken for many years. Commodity hardware can find a hash collision in seconds, meaning an attacker can easily generate the correct MD5 hash without using the correct password.

We use sha(pass.salt), and the salt is from /dev/random

SHA isn't quite as broken as MD5, but it shares the same theoretical weaknesses. Even without hash collisions, it is vulnerable to brute forcing. Modern hardware is so powerful it can try around a billion hashes a second. That means every 7 chracter password in the range [A-Za-z0-9] can be cracked in one hour on your average desktop computer.

If the only way to break the hash is to brute-force it, it's secure enough

It is unlikely that your database will be hacked and your hashes brute forced. However, in the event that it does happen, or SHA512 is broken, using this module gives you an easy way to change to a different algorithm, while still allowing you to validate old passphrases

KNOWN ISSUES ^

If you see errors like this

    Wide character in subroutine entry

or

    Input must contain only octets

The MD5, bcrypt, and SHA algorithms can't handle chracters with an ordinal value above 255, producing errors like this if they encounter them. It is not possible for this plugin to automagically work out the correct encoding for a given string.

If you see errors like this, then you probably need to use the Encode module to encode your text as UTF-8 (or whatever encoding it is) before giving it to passphrase.

Text encoding is a bag of hurt, and errors like this are probably indicitive of deeper problems within your app's code.

You will save yourself a lot of trouble if you read up on the Encode module sooner rather than later.

For further reading on UTF-8, unicode, and text encoding in perl, see http://training.perl.com/OSCON2011/index.html

SEE ALSO ^

Dancer, Digest, Crypt::Eksblowfish::Bcrypt, Dancer::Plugin::Bcrypt

AUTHOR ^

James Aitken <jaitken@cpan.org>

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2012 by James Aitken.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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