From eb0c8951196c637e44daf3c0617b131b997d5d2c Mon Sep 17 00:00:00 2001
From: Lena <lena@omega>
Date: Thu, 1 Jan 2026 00:00:00 +0000
Subject: scrcpy-android: mirror an Android device over wireless ADB

Native Java app for Android 12+ that mirrors another Android
device over wireless ADB, forwarding video, audio, touch input,
and clipboard. Bundles a pinned scrcpy-server.jar and the
vendored libadb-android stack. Supports h264/h265/av1 video and
raw/opus audio with in-app codec selection. No NDK, no Kotlin.
Includes JVM unit tests and a Docker-based emulator e2e rig.
---
 test-rig/Keygen.java | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 test-rig/Keygen.java

(limited to 'test-rig/Keygen.java')

diff --git a/test-rig/Keygen.java b/test-rig/Keygen.java
new file mode 100644
index 0000000..8cb90a6
--- /dev/null
+++ b/test-rig/Keygen.java
@@ -0,0 +1,92 @@
+// Read a DER-encoded PKCS#8 RSA private key, derive the public key,
+// emit the Android adb_keys line on stdout.
+//
+//   java test-rig/Keygen.java <path/to/adbkey.der>
+//
+// The Android pubkey blob format (from system/core/libcrypto_utils):
+//   uint32_t modulus_size_words;   // = 64 for RSA-2048
+//   uint32_t n0inv;                // -1 / N[0] mod 2^32
+//   uint8_t  modulus[256];         // little-endian
+//   uint8_t  rr[256];              // (2^2048)^2 mod N, little-endian
+//   uint32_t exponent;             // typically 65537
+// = 524 bytes, then base64-encoded, then " scrcpy-android@test".
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.KeyFactory;
+import java.security.PrivateKey;
+import java.security.interfaces.RSAPrivateCrtKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.PKCS8EncodedKeySpec;
+import java.security.spec.RSAPublicKeySpec;
+import java.util.Base64;
+
+public final class Keygen {
+
+    private static final int MODULUS_SIZE       = 256;             // bytes (2048 / 8)
+    private static final int MODULUS_SIZE_WORDS = MODULUS_SIZE / 4;
+    private static final int ENCODED_SIZE       = 3 * 4 + 2 * MODULUS_SIZE;
+
+    public static void main(String[] args) throws Exception {
+        if (args.length != 1) {
+            System.err.println("usage: java Keygen.java <der private key path>");
+            System.exit(2);
+        }
+        byte[] der = Files.readAllBytes(Path.of(args[0]));
+        PrivateKey priv = KeyFactory.getInstance("RSA")
+                .generatePrivate(new PKCS8EncodedKeySpec(der));
+        RSAPublicKey pub = derivePublic(priv);
+
+        byte[] blob = encode(pub);
+        String b64 = Base64.getEncoder().encodeToString(blob);
+        System.out.print(b64);
+        System.out.println(" scrcpy-android@test");
+    }
+
+    private static RSAPublicKey derivePublic(PrivateKey priv) throws Exception {
+        if (priv instanceof RSAPrivateCrtKey crt) {
+            RSAPublicKeySpec spec = new RSAPublicKeySpec(crt.getModulus(), crt.getPublicExponent());
+            return (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(spec);
+        }
+        throw new IOException("private key is not an RSAPrivateCrtKey");
+    }
+
+    private static byte[] encode(RSAPublicKey pub) {
+        ByteBuffer buf = ByteBuffer.allocate(ENCODED_SIZE).order(ByteOrder.LITTLE_ENDIAN);
+        BigInteger n = pub.getModulus();
+
+        buf.putInt(MODULUS_SIZE_WORDS);
+
+        // n0inv = (2^32) - (N[0] mod 2^32)^-1 mod 2^32
+        BigInteger r32   = BigInteger.ZERO.setBit(32);
+        BigInteger n0inv = n.mod(r32).modInverse(r32);
+        n0inv = r32.subtract(n0inv);
+        buf.putInt(n0inv.intValue());
+
+        buf.put(beToLe(MODULUS_SIZE, n));
+
+        // rr = (2^(MODULUS_SIZE*8))^2 mod N
+        BigInteger rr = BigInteger.ZERO.setBit(MODULUS_SIZE * 8).modPow(BigInteger.TWO, n);
+        buf.put(beToLe(MODULUS_SIZE, rr));
+
+        buf.putInt(pub.getPublicExponent().intValue());
+        return buf.array();
+    }
+
+    private static byte[] beToLe(int len, BigInteger v) {
+        byte[] be = v.toByteArray();
+        // strip leading sign byte if present
+        int start = 0;
+        if (be.length > len) start = be.length - len;
+        byte[] out = new byte[len];
+        for (int i = 0; i < len; i++) {
+            int srcIdx = be.length - 1 - i;
+            if (srcIdx >= start) out[i] = be[srcIdx];
+        }
+        return out;
+    }
+}
-- 
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