1 files changed, 34 insertions, 0 deletions
diff --git a/notes/repo_details.md b/notes/repo_details.md
new file mode 100644
index 0000000..c16bb25
--- /dev/null
+++ b/notes/repo_details.md
@@ -0,0 +1,34 @@
+
+It seems like the current MST format does not match the current atproto docs
+(https://atproto.com/specs/atp), and some pieces are missing.
+
+## Repo Questions
+
+**What CID codec and hash is used?**
+
+For the IPLD nodes and MST tree, it looks like base32, dag-cbor, sha2-256, with
+256 bits of hash.
+
+**What cryptography is used for signatures?**
+
+Haven't dug through code yet to figure it out.
+
+**What is the auth_token (JWT) for?**
+
+Not sure, but it is often null in the current implementation. Maybe has to do
+with clients that don't have the full signing key?
+
+## MST Questions
+
+**How to determine "layer" of tree for a given key? AKA, how to count "leading zeros"?**
+
+- take hash of the full key (UTF-8 string)
+- encode in baseN format, depending on "fanout" configuration
+- the "zero char" is the char which encoding '0x00' (single zero byte) in the baseN codec, and taking the first char returned. this is usually (always?) '0'
+- for a given hashed+encoded key, count how many leading chars match the "zero char"
+
+**What is the prefix key compression relative to ("previous node")?**
+
+Based on output from the current implementation, it seems local to individual
+MST nodes. AKA, each MST node has enough information to recover all the keys
+for all the records indicated in that node.