fix: handle sliced Buffer byte ranges in ECDH/DH native bridge

example/src/tests/ecdh/ecdh_tests.ts

@@ -132,6 +132,44 @@ test(SUITE, 'should set private key and compute secret for secp256k1', () => {
   assert.strictEqual(secret1.toString('hex'), secret2.toString('hex'));
 });
 
+test(SUITE, 'should compute secret with sliced public key buffer', () => {
+  const alice = crypto.createECDH('secp256k1');
+  alice.generateKeys();
+
+  const bob = crypto.createECDH('secp256k1');
+  bob.generateKeys();
+
+  const bobPub = bob.getPublicKey() as Buffer;
+  assert.isTrue(Buffer.isBuffer(bobPub), 'public key should be a Buffer');
+
+  // Force non-zero byteOffset by slicing from a larger packet.
+  const packet = Buffer.concat([
+    Buffer.from([0xaa, 0xbb]),
+    bobPub,
+    Buffer.from([0xcc]),
+  ]);
+  const bobPubSlice = packet.slice(2, 2 + bobPub.length);
+  assert.strictEqual(
+    bobPubSlice.length,
+    bobPub.length,
+    'slice length should match key length',
+  );
+  assert.isAbove(
+    bobPubSlice.byteOffset,
+    0,
+    'slice should have non-zero byteOffset',
+  );
+
+  const secretFromOriginal = alice.computeSecret(bobPub);
+  const secretFromSlice = alice.computeSecret(bobPubSlice);
+
+  assert.strictEqual(
+    secretFromSlice.toString('hex'),
+    secretFromOriginal.toString('hex'),
+    'sliced public key should derive the same shared secret',
+  );
+});
+
 test(SUITE, 'getCurves - should return array of supported curves', () => {
   const curves = getCurves();
   assert.isArray(curves);

packages/react-native-quick-crypto/src/diffie-hellman.ts

@@ -2,6 +2,7 @@ import { NitroModules } from 'react-native-nitro-modules';
 import type { DiffieHellman as DiffieHellmanInterface } from './specs/diffie-hellman.nitro';
 import { Buffer } from '@craftzdog/react-native-buffer';
 import { DH_GROUPS } from './dh-groups';
+import { toArrayBuffer } from './utils/conversion';
 
 export class DiffieHellman {
   private _hybrid: DiffieHellmanInterface;
@@ -36,10 +37,7 @@ export class DiffieHellman {
         genBuf = Buffer.from(generator, encoding as BufferEncoding);
       }
 
-      this._hybrid.init(
-        primeBuf.buffer as ArrayBuffer,
-        genBuf.buffer as ArrayBuffer,
-      );
+      this._hybrid.init(toArrayBuffer(primeBuf), toArrayBuffer(genBuf));
     }
   }
 
@@ -62,7 +60,7 @@ export class DiffieHellman {
     }
 
     const secret = Buffer.from(
-      this._hybrid.computeSecret(keyBuf.buffer as ArrayBuffer),
+      this._hybrid.computeSecret(toArrayBuffer(keyBuf)),
     );
     if (outputEncoding) return secret.toString(outputEncoding);
     return secret;
@@ -99,7 +97,7 @@ export class DiffieHellman {
     } else {
       keyBuf = Buffer.from(publicKey, encoding);
     }
-    this._hybrid.setPublicKey(keyBuf.buffer as ArrayBuffer);
+    this._hybrid.setPublicKey(toArrayBuffer(keyBuf));
   }
 
   setPrivateKey(privateKey: Buffer | string, encoding?: BufferEncoding): void {
@@ -109,7 +107,7 @@ export class DiffieHellman {
     } else {
       keyBuf = Buffer.from(privateKey, encoding);
     }
-    this._hybrid.setPrivateKey(keyBuf.buffer as ArrayBuffer);
+    this._hybrid.setPrivateKey(toArrayBuffer(keyBuf));
   }
 
   get verifyError(): number {

packages/react-native-quick-crypto/src/ecdh.ts

@@ -1,6 +1,7 @@
 import { NitroModules } from 'react-native-nitro-modules';
 import type { ECDH as ECDHInterface } from './specs/ecdh.nitro';
 import { Buffer } from '@craftzdog/react-native-buffer';
+import { toArrayBuffer } from './utils/conversion';
 
 const POINT_CONVERSION_COMPRESSED = 2;
 const POINT_CONVERSION_UNCOMPRESSED = 4;
@@ -43,7 +44,7 @@ export class ECDH {
     }
 
     // ECDH.computeSecret in Node.js returns Buffer
-    const secret = this._hybrid.computeSecret(keyBuf.buffer as ArrayBuffer);
+    const secret = this._hybrid.computeSecret(toArrayBuffer(keyBuf));
     return Buffer.from(secret);
   }
 
@@ -58,7 +59,7 @@ export class ECDH {
     } else {
       keyBuf = Buffer.from(privateKey, encoding);
     }
-    this._hybrid.setPrivateKey(keyBuf.buffer as ArrayBuffer);
+    this._hybrid.setPrivateKey(toArrayBuffer(keyBuf));
   }
 
   getPublicKey(encoding?: BufferEncoding): Buffer | string {
@@ -80,7 +81,7 @@ export class ECDH {
     } else {
       keyBuf = Buffer.from(publicKey, encoding);
     }
-    this._hybrid.setPublicKey(keyBuf.buffer as ArrayBuffer);
+    this._hybrid.setPublicKey(toArrayBuffer(keyBuf));
   }
 
   static convertKey(
@@ -116,11 +117,7 @@ export class ECDH {
     }
 
     const result = Buffer.from(
-      ECDH.convertKeyHybrid.convertKey(
-        keyBuf.buffer as ArrayBuffer,
-        curve,
-        formatNum,
-      ),
+      ECDH.convertKeyHybrid.convertKey(toArrayBuffer(keyBuf), curve, formatNum),
     );
 
     if (outputEncoding) {