Basic Content Integrity Assurance; Integrity Seals; Validating Reads - Dell DX6000 Application Manual

Chapter 20. Basic Content Integrity Assurance
DX Storage provides some basic capabilities for allowing applications to obtain and validate integrity
guarantees on the stored data. Integrity here means an independently verifiable guarantee that
the data returned for a given name or UUID is exactly the same data that was stored using that
name or UUID, perhaps many months or years in the past. This is done by hashing the data using a
cryptographic hash algorithm; content metadata is not included in the hash. If the application stores
the name or UUID and its associated hash value, these can be used later to verify the content has
not changed, either through accidental or malicious means.

20.1. Integrity Seals

An integrity seal is a URL containing an object's name or UUID, its hash value, and the type of hash
algorithm that was used for the computations. An application can request an integrity seal when it
performs a WRITE by including a hashtype query string as follows:
POST http://company.cluster.com/?hashtype=md5 HTTP/1.1
Currently allowable hashtypes are md5, sha1, sha256, sha384, and sha512. After creating the
object and assigning a name or UUID, DX Storage replies with a 201 (Created) response that
includes a location header with a URL that can later be used to retrieve the data.
In addition to the host and name or UUID, the URL includes the hash type and hash value computed
from the content object. This URL, including the triple name or UUID, hash type, and hash, is
referred to as the integrity seal of the content object.
Following is an example of a complete integrity seal embedded in a Location header for an
unnamed object.
Location: http://129.69.251.143/41A140B5271DC8D22FF8D027176A0821?

20.2. Validating Reads

An integrity seal can be used in a subsequent READ request to validate the data stored in a DX
Storage cluster (any cluster). By supplying the URL returned in the Location header from the
WRITE request (perhaps replacing the host address if connected to a different cluster or node), the
application can ask DX Storage to validate while reading the data. For example:
GET http://129.69.251.143/41A140B5271DC8D22FF8D027176A0821?hashtype=md5&
Upon receiving such a READ request, DX Storage recomputes the hash of the stored content using
the supplied hashtype and compares the computed hash with the hash value in the integrity seal. If
the two values do not match, DX Storage send a 200 (OK) response but drops the connection prior
to sending the object content. If, on the other hand, the content has not been modified or corrupted
in any way, the hashes match and, in that case, DX Storage returns the object as usual with the
computed digest as a trailing Location header.
Because the hash algorithms are published and well-known, it is also possible for users and third
parties to independently validate an object that has been stored by DX Storage. This can be done
by reading its contents, computing the hash value, and comparing it with the hash value in the seal.
By publishing an integrity seal at the time it is created one can even provide indisputable evidence
Copyright © 2010 Caringo, Inc.
All rights reserved
hashtype=md5&hash=7A25E6067904EAC8002498CF1AE33023
hash=7A25E6067904EAC8002498CF1AE33023 HTTP/1.1
71
Version 5.0
December 2010