From fa8af6e1273503b6ebb71969a5260dc705ebe305 Mon Sep 17 00:00:00 2001
From: Shing Him Ng <shinghim@protonmail.com>
Date: Sun, 20 Jul 2025 16:56:41 -0500
Subject: [PATCH] Introduce Arbitrary crate and add PublicKey impl

---
 Cargo-minimal.lock |  7 +++++++
 Cargo-recent.lock  |  7 +++++++
 Cargo.toml         |  2 ++
 src/key.rs         | 22 ++++++++++++++++++++++
 4 files changed, 38 insertions(+)

diff --git a/Cargo-minimal.lock b/Cargo-minimal.lock
index 1b944bb7b..43c294268 100644
--- a/Cargo-minimal.lock
+++ b/Cargo-minimal.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "arbitrary"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dde20b3d026af13f561bdd0f15edf01fc734f0dafcedbaf42bba506a9517f223"
+
 [[package]]
 name = "arrayvec"
 version = "0.7.6"
@@ -224,6 +230,7 @@ checksum = "ea6a9290e3c9cf0f18145ef7ffa62d68ee0bf5fcd651017e586dc7fd5da448c2"
 name = "secp256k1"
 version = "0.31.1"
 dependencies = [
+ "arbitrary",
  "bincode",
  "bitcoin_hashes",
  "getrandom",
diff --git a/Cargo-recent.lock b/Cargo-recent.lock
index c33758e78..ffdc4af39 100644
--- a/Cargo-recent.lock
+++ b/Cargo-recent.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "arbitrary"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dde20b3d026af13f561bdd0f15edf01fc734f0dafcedbaf42bba506a9517f223"
+
 [[package]]
 name = "arrayvec"
 version = "0.7.6"
@@ -215,6 +221,7 @@ checksum = "e1cf6437eb19a8f4a6cc0f7dca544973b0b78843adbfeb3683d1a94a0024a294"
 name = "secp256k1"
 version = "0.31.1"
 dependencies = [
+ "arbitrary",
  "bincode",
  "bitcoin_hashes",
  "getrandom",
diff --git a/Cargo.toml b/Cargo.toml
index 71acbf4a2..948a5769d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,10 +32,12 @@ global-context = ["std"]
 # if you are doing a no-std build, then this feature does nothing
 # and is not necessary.)
 global-context-less-secure = ["global-context"]
+arbitrary = ["dep:arbitrary"]
 
 [dependencies]
 secp256k1-sys = { version = "0.11.0", default-features = false, path = "./secp256k1-sys" }
 
+arbitrary = { version = "1.4", optional = true }
 hashes = { package = "bitcoin_hashes", version = "0.14", default-features = false, optional = true }
 rand = { version = "0.9", default-features = false, optional = true }
 serde = { version = "1.0.103", default-features = false, optional = true }
diff --git a/src/key.rs b/src/key.rs
index e446afe7f..5bb9c3810 100644
--- a/src/key.rs
+++ b/src/key.rs
@@ -6,6 +6,8 @@
 use core::ops::{self, BitXor};
 use core::{fmt, ptr, str};
 
+#[cfg(feature = "arbitrary")]
+use arbitrary::{Arbitrary, Unstructured};
 use secp256k1_sys::secp256k1_ec_pubkey_sort;
 #[cfg(feature = "serde")]
 use serde::ser::SerializeTuple;
@@ -1653,6 +1655,26 @@ impl<C: Verification> Secp256k1<C> {
     }
 }
 
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for PublicKey {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let mut bytes = [0u8; 33];
+        loop {
+            // Unstructured::fill_buffer pads the buffer with zeroes if it runs out of data
+            if u.len() < 33 {
+                return Err(arbitrary::Error::NotEnoughData);
+            }
+
+            bytes[0] = if u.arbitrary::<bool>()? { 0x02 } else { 0x03 };
+            u.fill_buffer(&mut bytes[1..])?;
+
+            if let Ok(pk) = PublicKey::from_slice(&bytes) {
+                return Ok(pk);
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 #[allow(unused_imports)]
 mod test {