Accessing Data on Skynet

Beyond the File Upload
Now that you have uploaded a file to Skynet, you'll see some of the ways you can use the network to access data, taking a closer look at skylinks before learning about SkyDB and HNS domains.
Skylinks
In the last section, you learned that you can't edit skyfiles (files hosted on Skynet). It's important to know that this is not a limitation, but a design feature! Data that cannot change is called immutable, and in this section, we'll see how that helps power Skynet.
Anatomy of a Skylink
Remember, when we uploaded a file to Skynet, we got back a wild-looking URL. Here's an example: https://siasky.net/CADIvje1Fdy2FP2TeBsYAbHfUsNug98wE7SYArdyczDaDg​
This URL has two distinct parts:
1.The Portal URL, which points to the portal you're using to access Skynet: https://siasky.net/
2.The information needed to locate and pull your file from Skynet -- its skylink: CADIvje1Fdy2FP2TeBsYAbHfUsNug98wE7SYArdyczDaDg
Skylinks are usually written with sia:// at the beginning. A skylink will point to the same file, no matter what portal you use, so the portal is not included. For the link above, we'd write the skylink assia://CADIvje1Fdy2FP2TeBsYAbHfUsNug98wE7SYArdyczDaDg
How Skylinks are Generated (and Why They're So Strange Looking)
Although skylinks can look random, their structure is essential to the security of Skynet.
When a file is put on Skynet, the data in the file is hashed using a cryptographic function. This hash, along with some additional info, is used to generate the skylink. Because of this process, Skynet portals can always confirm that the file they receive from hosts hasn't been altered, because a different file would result in a different hash! This is also why you can't edit files on Skynet -- if you try to change a file's contents, its hash changes, and so the skylink would have to change too.
If "hashing" is unfamiliar to you, just imagine it as doing some math to make a fingerprint for a file. The fingerprint remains small, even if the file is quite large, and if the file changes, its fingerprint changes.
Skylink Alternatives
Some sites and applications will put a modified version of the skylink before the portal domain. We'll walk through how to do this (and why you might want to) on the Skylinks page.
Skylink Limitations
You don't always want cryptic URLs for data you can't edit. Sometimes you want data to be mutable or URLs that are human-readable. Let's take a look at how SkyDB and Handshake Names solve these issues.
SkyDB & The Registry
Skynet uses registry entries and SkyDB entries to enable mutable content on the network. Most users won't directly interact with these, but they're what powers content-rich web applications on Skynet.
Registry Entries
Registry entries are a special type of content that can be updated. Registry entries are very, very small -- just big enough to point to a Skyfile and keep track of how many times they've been updated. They also use cryptography that lets anyone with the right info to read an entry while only those with a special key can update it.
SkyDB
Used alone, registry entries aren't that exciting for the average user since you can't fit much information in such a small space. What they power though is our database solution called SkyDB. SkyDB uses the registry entries to make powerful web applications possible. By taking advantage of the registry's mutability at a consistent URL, SkyDB can create updatable data by updating registry entries to point at the skylink of newly created data.
SkyDB entries themselves take the form of JSON files, a standard format used across the web for storing information and sharing data between applications. With SkyDB, you can store info like a follower-list or a user profile and take it with you from skapp to skapp. This is a crucial piece of building Web3 -- you control your data and which apps get to access it.
You won't usually see them typed out, but when typed as URLs, registry entries look like this: https://siasky.net/skynet/registry?publickey=ed25519%3Ab4f9e43178222cf33bd4432dc1eca49499397ecd1f7de23b568f3fa1e72e5c7c&datakey=79c05b4b67764ad99a7976a7d2fb1cfce4f196ea217ef0356af042cb5492bd5d
Handshake Names
If you'll remember back to Using Skynet, none of the skapps had strange URLs. That's because they use something called Handshake Names (or HNS).
Handshake is a decentralized domain name project that Skynet Portals support out-of-the-box. Developers can bid on and purchase domain names and then link them to data and applications on Skynet. Let's look quickly at what this means for Skynet users.
As we saw in Using Skynet, you'll typically see HNS links look like this:
https://<hns-name>.hns.siasky.net
For more in-depth details about the Handshake and how it interacts with Skynet, see Handshake Names.
Benefits
When you own a handshake name, you're not "leasing" it like with .com names -- you own the name and gain censorship resistance beyond what traditional domains can give you. If Mr. GoDaddy gets cross with you, you won't have to worry about your access to your domain names being revoked.
Skynet Portals take care of figuring out where on Skynet an HNS name points. Handshake names can point to applications, user profiles, and more.
One great use-case for HNS names is the fully decentralized profile platform dLinks. Hosted using Skynet, this service lets you use your Handshake name to host a simple profile full of links that your friends and community can always trust to be available and under your control.
Trade-offs
With Handshake names, you gain access to a URL that's easy to remember (not to mention keeps developers from having to update the links to their skapp every time they want to make a small update). The trade-off to keep in mind is that, as a user, you may not want an app's underlying code to change!
By using HNS, we re-introduce an issue to Skynet that we claimed was a benefit over the traditional web. When going to a site using HNS, you can't guarantee the data or code hasn't changed, unless you can confirm that the skyfile that the name points to has the same skylink as before. And immutable data was our major feature! It's a trade-off of convenience, and, for most user-facing applications, it's best to prioritize making content convenient and accessible.
As we get deeper into the design and functions of Skynet, you'll see there are often multiple ways of achieving a similar result. It's important to realize that this flexibility is necessary because there are trade-offs when choosing one option over another, especially when designing applications.