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+# Auto Updates
+
+## Theory
+* Using a specific git commit (e.g. abcdef123) we produce a determinstic JAR with consistent hash.
+* To avoid issues with over-eager anti-virus / firewalls we obfuscate JAR using very simplistic XOR-based method.
+* Obfuscated JAR is uploaded to various well-known locations, usually including github itself, referenced in settings.
+* An `ARBITRARY` transaction is published by a **non-admin** member of the "dev" group (groupID 1) with:
+	+ 'service' set to 1
+	+ txGroupId set to dev groupID, i.e. 1 
+and containing this data:
+    + git commit's timestamp in milliseconds (8 bytes)
+    + git commit's SHA1 hash (20 bytes)
+    + SHA256 hash of *obfuscated* JAR (32 bytes)
+* Admins of dev group approve above transaction until it reaches, or exceeds, dev group's approval threshold (e.g. 60%).
+* Nodes notice approved transaction and begin auto-update process of:
+    + checking transaction's timestamp is greater than node's current build timestamp
+    + checking git commit timestamp (in data payload) is greater than node's current build timestamp
+    + downloading update (obfuscated JAR) from various locations using git commit SHA1 hash
+    + checking downloaded update's SHA256 hash matches hash in transaction's data payload
+    + calling ApplyUpdate Java class to shutdown, update and restart node
+
+## Obfuscation method
+The same method is used to obfuscate and de-obfuscate:
+* XOR each byte of the file with 0x5A
+
+## Typical download locations
+The git SHA1 commit hash is used to replace `%s` in various download locations, e.g.:
+* https://github.com/QORT/qortal/raw/%s/qortal.update
+* https://raw.githubusercontent.com@151.101.16.133/QORT/qortal/%s/qortal.update
+
+These locations are part of the org.qortal.settings.Settings class and can be overriden in settings.json like:
+```
+  "autoUpdateRepos": [
+    "http://mirror.qortal.org/auto-updates/%s",
+    "https://server.host.name@1.2.3.4/Qortal/%s"
+  ]
+```
+The latter entry is an example where the IP address is provided, bypassing name resolution, for situations where DNS is unreliable or unavailable.
+
+## XOR tool
+To help with manual verification of auto-updates, there is a XOR tool included in the Qortal JAR.
+It can be used thus:
+```
+$ java -cp qortal.jar org.qortal.XorUpdate
+usage: XorUpdate <input-file> <output-file>
+$ java -cp qortal.jar org.qortal.XorUpdate qortal.jar qortal.update
+$
+```
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