vmod_digest

Varnish Digest Module

Manual section:	3
Author:	Kristian Lyngstøl
Date:	2016-03-16
Version:	1.0.3

SYNOPSIS

import digest;

digest.hmac_md5(<key>,<message>);
digest.hmac_sha1(<key>, <message>);
digest.hmac_sha256(<key>, <message));

digest.base64(<string>);
digest.base64url(<string>);
digest.base64url_nopad(<string>);
digest.base64_hex(<string>);
digest.base64url_hex(<string>);
digest.base64url_nopad_hex(<string>);
digest.base64_decode(<string>);
digest.base64url_decode(<string>);
digest.base64url_nopad_decode(<string>);

digest.version()

digest.hash_sha1(<string>);
digest.hash_sha224(<string>);
digest.hash_sha256(<string>);
digest.hash_sha384(<string>);
digest.hash_sha512(<string>);
digest.hash_gost(<string>);
digest.hash_md2(<string>);
digest.hash_md4(<string>);
digest.hash_md5(<string>);
digest.hash_crc32(<string>);
digest.hash_crc32b(<string>);
digest.hash_adler32(<string>);
digest.hash_haval128(<string>);
digest.hash_haval160(<string>);
digest.hash_haval192(<string>);
digest.hash_haval224(<string>);
digest.hash_haval256(<string>);
digest.hash_ripemd128(<string>);
digest.hash_ripemd160(<string>);
digest.hash_ripemd256(<string>);
digest.hash_ripemd320(<string>);
digest.hash_tiger(<string>);
digest.hash_tiger128(<string>);
digest.hash_tiger160(<string>);
digest.hash_snefru128(<string>);
digest.hash_snefru256(<string>);

DESCRIPTION

Varnish Module (vmod) for computing HMAC, message digests and working with base64.

All HMAC- and hash-functionality is provided by libmhash, while base64 is implemented locally.

FUNCTIONS

Example VCL:

backend foo { ... };

import digest;

sub vcl_recv {
        if (digest.hmac_sha256("key",req.http.x-data) != req.http.x-data-sig)
        {
                return (synth(401, "Naughty user!"));
        }
}

hmac_(hash)

Prototype

digest.hmac_md5(<key>,<message>);
digest.hmac_sha1(<key>, <message>);
digest.hmac_sha256(<key>, <message));

Returns

String. Hex-encoded prepended with 0x.

Description

All the various hmac-functions work the same, but use a different hash mechanism.

Example

set resp.http.x-data-sig =
        digest.hmac_sha256("secretkey",resp.http.x-data);

base64, base64url, base64url_nopad

Prototype

digest.base64(<string>);
digest.base64url(<string>);
digest.base64url_nopad(<string>);

Returns

String

Description

Returns the base64-encoded version of the input-string. The base64url-variant uses base64 url-encoding (+/ replaced by -_) and the base64url_nopad does the same, but avoids adding padding. The latter is more commonly used, though an (allowed) exception to the RFC4648.

Example

set resp.http.x-data-sig =
        digest.base64({"content with
        newline in it"});

base64_hex, base64url_hex, base64url_nopad_hex

Prototype

digest.base64_hex(<string>);
digest.base64url_hex(<string>);
digest.base64url_nopad_hex(<string>);

Returns

String

Description

Returns the base64-encoded version of the hex encoded input-string. The input-string can start with an optional 0x. Input is hex-decoded into binary and the encoding is identical to base64, base64url, and base64url_nopad.

Example

set resp.http.x-data-sig =
        digest.base64_hex("0xdd26bfddf122c1055d4c");

hash_(algorithm)

Prototype

digest.hash_sha1(<string>);
digest.hash_sha224(<string>);
digest.hash_sha256(<string>);
digest.hash_sha384(<string>);
digest.hash_sha512(<string>);
digest.hash_gost(<string>);
digest.hash_md2(<string>);
digest.hash_md4(<string>);
digest.hash_md5(<string>);
digest.hash_crc32(<string>);
digest.hash_crc32b(<string>);
digest.hash_adler32(<string>);
digest.hash_haval128(<string>);
digest.hash_haval160(<string>);
digest.hash_haval192(<string>);
digest.hash_haval224(<string>);
digest.hash_haval256(<string>);
digest.hash_ripemd128(<string>);
digest.hash_ripemd160(<string>);
digest.hash_ripemd256(<string>);
digest.hash_ripemd320(<string>);
digest.hash_tiger(<string>);
digest.hash_tiger128(<string>);
digest.hash_tiger160(<string>);
digest.hash_snefru128(<string>);
digest.hash_snefru256(<string>);

Returns

String

Description

Computes the digest/hash of the supplied, using the specified hash algorithm. If in doubt as to which to pick, use SHA256. For detailed discussions, see The Internet.

Example

set resp.http.x-data-md5 =
        digest.hash_md5(resp.http.x-data);

base64_decode, base64url_decode, base64url_nopad_decode

Prototype

digest.base64_decode(<string>);
digest.base64url_decode(<string>);
digest.base64url_nopad_decode(<string>);

Returns

String

Description

Decodes the bas64 and base64url-encoded strings. All functions treat padding the same, meaning base64url_decode and base64url_nopad_decode are identical, but available for consistency and practicality.

Example

::

synthetic(digest.base64_decode(req.http.x-parrot));

version

Prototype

digest.version()

Returns

string

Description

Returns the string constant version-number of the digest vmod.

Example

set resp.http.X-digest-version = digest.version();

INSTALLATION

The source tree is based on autotools to configure the building, and does also have the necessary bits in place to do functional unit tests using the varnishtest tool.

Building requires the Varnish header files and uses pkg-config to find the necessary paths.

Usage:

./autogen.sh
./configure

If you have installed Varnish to a non-standard directory, call autogen.sh and configure with PKG_CONFIG_PATH pointing to the appropriate path. For example, when varnishd configure was called with --prefix=$PREFIX, use

PKG_CONFIG_PATH=${PREFIX}/lib/pkgconfig export PKG_CONFIG_PATH

Make targets:

• make - builds the vmod.
• make install - installs your vmod.
• make check - runs the unit tests in src/tests/*.vtc
• make distcheck - run check and prepare a tarball of the vmod.

AUTHOR

Original author: Kristian Lyngstøl <opensource@varnish-software.com>.

This Vmod was written for Media Norge, Schibsted and others.

The bulk of the functionality is acquired through libmhash.

BUGS

No bugs at all!

If the key is NULL for hmac-functions, the function will fail and return NULL itself, and do no hmac-computation at all. This should be used as an indication of some greater flaw in your software/VCL. (I.e.: Your key should be under your control, not user-supplied without verification).

The base64url_nopad_decode() and base64url_decode() functions do not differ much. The exception is that nopad_decode() does not know about padding at all, and might get confused if the input actually is padded.

SEE ALSO

• libmhash
• varnishd(1)
• vcl(7)
• https://github.com/varnish/libvmod-digest