From e4250e0e589b51a7a2dd2b2434393205788476fd Mon Sep 17 00:00:00 2001
From: fria <138676274+friadev@users.noreply.github.com>
Date: Mon, 14 Jul 2025 06:36:47 -0500
Subject: [PATCH] add sketch matrix

---
 blog/posts/differential-privacy.md | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/blog/posts/differential-privacy.md b/blog/posts/differential-privacy.md
index 260d7294..8d18d356 100644
--- a/blog/posts/differential-privacy.md
+++ b/blog/posts/differential-privacy.md
@@ -181,3 +181,10 @@ They limit the number of contributions any one user can make via a *privacy budg
 - Safari Crashing Domains
 - Health Type Usage
 
+That's just based on their initial whitepaper, they've likely increased their use of DP since then.
+
+### Sketch Matrix
+
+Apple uses a similar method to Google, with a matrix initialized with all zeros. The input for the matrix is encoded with the SHA-256 hashing algorithm, and then bits are flipped randomly at a probablility dependent on the epsilon value.
+
+Apple only sends a random row from this matrix instead of the entire thing in order to stay within their privacy budget.
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