NAME Object::Signature::Portable - generate portable signatures of objects SYNOPSIS use Object::Signature::Portable; my $sig = signature( $object ); # MD5 hex of object signature my $sig = signature( digest => 'SHA1', # SHA-1 digest format => 'b64udigest', # as URL-safe base-64 data => $object, ); DESCRIPTION This module provides a simple function for generating *portable* cryptographic signatures of Perl data structures. The object is serialized into a canonical JSON structure, and then hashed using the MD5 algorithm. Any two machines running different versions of Perl on different architectures should produce identical signatures. Note that this module is useful in cases where the consistency of signatures between machine is more important than the speed of signature generation. However, the serialization method, hash algorithm and signature format can be customized, as needed. EXPORTS "signature" my $sig = signature( $data ); my $sig = signature( data => $data, digest => 'MD5', # default format => 'hexdigest', # default serializer => sub { ... }, ); Generate a cryptographic signature of the $data. The following options are supported: "digest" The cyptographic digest algorithm, as supported by Crypt::Digest. Note that for most purposes (detecting when two Perl data structures are the same), MD5 is probably good enough. However, if you are hashing that in part comes from untrusted sources, or the consequences of two different data structures having the same signature are significant, then you should consider using a different algorithm. "format" The Crypt::Digest formatting method for the signature, which can be one of: "digest" The raw bytes of the digest. "hexdigest" The digest as a string of hexidecimal numbers. "b64digest" The digest as a MIME base-64 string. "b64udigest" The digest as a URL-friendly base-64 string. "prefix" If set to a true value, the digest is prefixed by the name of the digest algorithm. This is useful when you may want to change the digest algorithm used by an application in the future, but do not want to regenerate signatures for existing objects in a data store. "serializer" The serialization method, which is a subroutine that takes the data as a single argument, and returns the serialized data to be hashed. It is recommended that you use a serializer that produces canonical (normalized) output, and preferably one that produces consistent output across all of the platforms that you are using. By default, it uses JSON::MaybeXS. See "LIMITATIONS" below. LIMITATIONS By default, this module uses JSON::MaybeXS to serialize Perl objects. This requires the objects to have a "TO_JSON" method in order to be serialized. Unfortunately, this is not suitable for many objects (particularly those generated by modules that are not under your control, e.g. many CPAN modules) without monkey-patching or subclassesing them. One solution is to use a different serializer that can handle the object. Alternatively, you can write a wrapper function that uses a module such as Object::Serializer to translate an object into a hash reference that can then be passed to the "signature" function, e.g. package Foo; use parent 'Object::Serializer'; use Object::Signature::Portable (); sub signature { my $self = shift; return Object::Signature::Portable::signature( data => $self->serialize ); } Note that Object::Serializer allows you to define custom serialization strategies for various reference types. SEE ALSO Similar Modules Object::Signature This uses Storable to serialise objects and generate a MD5 hexidecimal string as a signature. This has the drawback that machines with different architectures, different versions of Perl, or different versions Storable may not produce the same signature for the same data. (This does not mean that Storable is unable to de-serialize data produced by different versions; it only means that the serialized data is not identical across different versions.) Object::Signature does not allow for customizing the hash algorithm or signature format. Object::Signature::Portable module can replicate the signatures generated by Object::Signature, using the following: use Storable 2.11; my $sig = signature( data => $data, serializer => sub { local $Storable::canonical = 1; return Storable::nfreeze($_[0]); }, ); As noted above, using Storable will not produce portable signatures. AUTHOR Robert Rothenberg (on behalf of Foxtons, Ltd.) LICENSE AND COPYRIGHT Copyright 2013 Robert Rothenberg. 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