What is SHSH? Save SHSH for what? Some notes about SHSH.

SHSH , or SHSH2 or Blobs can be considered the same. So what is SHSH?

=> Understand simply, when upgrading an iOS version, your device will send a request to Apple, Apple will then issue you a file like a " ticket " to allow you to upgrade iOS. Saving SHSH is saving that " ticket " => You can later use it to upgrade / downgrade iOS to a saved SHSH iOS version with the ticket Apple issued you previously. (Note to downgrade, SEP needs to be compatible, SHSH is only a part)

Example: You are on iOS 13.5.1 and have saved the SHSH of iOS 13.5. Because SEP of iOS 13.5.1 is compatible with SEP of iOS 13.5 => Can downgrade from 13.5.1 to 13.5 (although iOS 13.5 is not signed).

You do not need to raise iOS to save SHSH. That means you can still save the SHSH of iOS 13.5 even when you are on iOS 11, 12, ...
SHSH can only be saved for the version of the iOS version currently open.
Each machine has its own SHSH. Stored SHSH cannot be obtained from one device for another.
For A12 + devices, you must jailbreak first to be able to save SHSH.

Proceed (2 steps)

For non-jailbroken machines: (A12 + not jailbroken will NOT save SHSH)

Step 1: Get the machine's ECID

Plug the phone into the computer. Open 3uTools, right on the first tab, select "View iDevice Details". Here will be the ECID of the machine. (You should save ECID for convenience next time).
For the iPhone 6s / 6s + / SE (A9), since the Chip is manufactured by both TMSC and SamSung, there will be 2 chip models. You see the Model line to determine the type of Chip.

Step 2: Save SHSH

Once you have an ECID, you can now save SHSH. There are two ways to save SHSH, use https://shsh.host/ or https://tsssaver.1conan.com/ These two tools are basically equivalent.

Option 1: Use https://shsh.host/

- Go to https://shsh.host/ and follow in the picture.

- Note that iPhone 6s / 6s + / SE will have " Platform " line. This is the model you check in step 1.

- Check saved SHSH: After saving, go to “Find My”, enter ECID and press confirm to check the saved SHSH.

Method 2: Use https://tsssaver.1conan.com/

- The information to be filled out is similar to the one above.

- Tsssaver's saved SHSH will be more complicated. First you enter ECID in the line "Recover SHSH Link" to open the folder to save SHSH. SHSH files are usually located in the folder "noapnonce" (see photo for clarification).

For jailbroken machines.

- The jailbroken device is simple then, just install tweak " System Info " (source https://apt.arx8x.net/ ) to be able to see all the information of the device.

- You can also manually save SHSH above. Or you can save SHSH by System Info always: Open Setting => General => About => ECID => Swipe left and select Save SHSH2. This way SHSH can be saved for the A12 + device as well

- Select the iOS version is done. The SHSH file will be saved both locally and on shsh.host. (How to check the file saved at shsh.host above)

So you have successfully saved SHSH to serve to upgrade / downgrade iOS later. The whole process only takes a few minutes, quite simply. If possible, I will write instructions to downgrade iOS with shsh just saved.

Good luck!

Ps: Particularly for A12 +, there is another way to save Blobs, you can refer here. Since there are no test conditions, I cannot be sure which one is better.