vault backup: 2025-09-24 16:53:28

Author: blacklightpy

.obsidian/workspace.json

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01. Personal/Daily Notes/Entry of 24th Sep, 2025.md

@@ -352,6 +352,7 @@ A problem with USB Mass Storage was that, it would expose the device at the bloc
 		- Disables DM-Verity and ForceEncrypt
 - Disable Verity in vbmeta.img
 	- `fastboot --disable-verification --disable-verity flash vbmeta vbmeta.img`
+	- Or, as I've learned, flashing a blank vbmeta.img is another solution
 - Factory Reset Protection (FRP)
 	- It is used to prevent others from using your device after factory resetting it
 	- You can disable it by wiping the FRP partition

06. Collected Knowledge/xAndroid Boot Internals.md

@@ -0,0 +1,21 @@
+# Physically
+
+A block device, physically simply means a device that stores data in blocks or allocation units.
+# Software
+
+In software, by block device, we would be referring to the drivers for parsing block devices.
+## In Linux
+
+In Linux, you can only mount block devices.
+
+### About reading block devices directly
+
+I wrote in [[loop devices]] that you can only mount block devices, and loop devices are block devices created for disk images.
+
+But someone asked a query about mounting a block device as a file, so that he doesn't have to make a disk image with `dd` for a recovery utility to read from it.
+
+In this case, usually, you would be able to `cat` a block device to read the contents, and `dd` does pretty much that. But the block device descriptor file itself is not the same as the block device.
+
+If you do `stat` on a block device, you will see that it has a size of `0` bytes, and it will be called a "block special file" as opposed to a "regular file" with a size.
+
+#rough #advaita-analogy The above line gave me an analogy - we say Nirguna Brahman is without any utility - literally Nir-Guna. And I used to have analogies for why that isn't a bad thing. In this example, similarly, a block device has `0` file size. But if you `cat` a block device, you will get a lot of data. Because while a block device is empty in size, it is what allows you to read the physical block device.

Block Devices.md

@@ -0,0 +1,9 @@
+There are block ciphers (which encrypt by blocks) and stream ciphers (which encrypt bit-by-bit).
+
+My Samsung (R) Galaxy M10 (SM-M105F / m10lte) used an MMC storage, and it used FDE with AES-XTS by default (It shows `aes-xts-disk` in its crypto footer).
+
+There is a Stack Overflow question ([Question 49335046: Android 4.4 FDE (Scrypt Footer)][https://stackoverflow.com/question/49335046]), where a user took the 16 KB crypto footer from his encrypted `userdata` partition, from his Samsung Galaxy S4 Mini running Android 4.4.4.
+
+He was learning about FDE, and though Android 4.4.4 does not have FDE (EDIT: I was wrong, see next paragraph), it has Scrypt. He also found that there is very less documentation on it, and he found that the 16 KB crypto footer started with the [[Magic Numbers (in Linux)|magic number]] `0xC5B1B5D0`.
+
+Actually, my Galaxy M10 also has the same magic number, so I wonder if it is related, but it's more likely to have FDE. Oh, turns out Samsung introduced FDE in Android 4.4.4 as opt-in, and made it default from Android 7.0.

Disk Encryption Theory.md

@@ -0,0 +1,3 @@
+See [How to Downgrade Android Version in Samsung Devices if Device is in Higher Binery | XDA Forums](https://xdaforums.com/t/how-to-downgrade-android-version-in-samsung-devices-if-device-is-in-higher-binery.4561665/)
+
+

How to downgrade Samsung Binaries.md

@@ -0,0 +1,15 @@
+Actually, UNIX-like systems can only mount block devices. You do not really mount files.
+
+> [!NOTE]
+> As for why they are called loop devices - that's something unsettled. In UNIX Stack Exchange, user schily said that he created the feature first on SunOS 4.0, which he called `fbk` (file emulates block device); and he complains that Linux seems to use a wrong name for that feature.
+> 
+> According to others, loop is short for "loopback" - and some say it was chosen to show how the block devices are looped back. I don't know what it means. Solaris 8 introduced `lofi` (loopback file) which worked similarly, and BSD introduced them under the name `vnd` (`vnode` disk).
+
+So `losetup` can be used to create a loop device as `/dev/loopN` based on a disk image. More precisely, a block device is any device in `/dev`. A loop device is a block device for a disk image file.
+
+And only loop devices are mounted using `mount`. When you use `mount` on a disk image, thought it seems direct, it actually runs `losetup` under the hood. In fact, the option `-o loop` does exactly that.
+
+If the disk image contains many partitions, you cannot mount it as a single file system. You you have to inspect the partition table, using a utility like `fdisk` or `gdisk`, and then create loop devices for the specific offsets of the image, and mount them.
+
+`kpartx` from `util-linux` used to do that automatically, and now `losetup` has an option that does that as well.
+

Loop Devices.md

@@ -0,0 +1,3 @@
+I'm referring to these in Linux, not numerology.
+
+They are numbers that somehow identify certain features. Have to learn more about them.

Magic Numbers (in Linux).md

@@ -0,0 +1,6 @@
+
+Implementations:
+
+- ARM TrustZone
+	- Qualcomm Trusted / Secure Execution Environment (QTEE / QSEE)
+	- Samsung Knox