diff --git a/README.md b/README.md
index cf79832..46ced15 100644
--- a/README.md
+++ b/README.md
@@ -115,7 +115,7 @@ hydentity/
 
 ```bash
 # Clone the repository
-git clone https://github.com/your-org/hydentity.git
+git clone https://github.com/hydex-org/hydentity.git
 cd hydentity
 
 # Install dependencies
diff --git a/packages/hydentity-sdk/src/client/hydentity-client.ts b/packages/hydentity-sdk/src/client/hydentity-client.ts
index fa47f03..8652702 100644
--- a/packages/hydentity-sdk/src/client/hydentity-client.ts
+++ b/packages/hydentity-sdk/src/client/hydentity-client.ts
@@ -28,7 +28,11 @@ import {
 } from '../instruction-builders/vault';
 import { buildUpdatePolicyInstruction, createUpdatePolicyParams } from '../instruction-builders/policy';
 import { buildAddDelegateInstruction, buildRevokeDelegateInstruction } from '../instruction-builders/delegate';
-import { HYDENTITY_PROGRAM_ID } from '../constants';
+import {
+  HYDENTITY_PROGRAM_ID,
+  POLICY_MASTER_SEED_SIGN_MESSAGE,
+} from '../constants';
+import { derivePolicyMasterSeedFromSignature } from '../utils/randomness';
 
 /**
  * Configuration options for HydentityClient
@@ -129,6 +133,21 @@ export class HydentityClient<T = SolanaTransactionSignature> {
     return this.signer.getPublicKey();
   }
 
+  /**
+   * Per-wallet entropy for PolicyEngine splits/delays (from signing POLICY_MASTER_SEED_SIGN_MESSAGE).
+   */
+  private async derivePolicyMasterSeed(): Promise<Uint8Array> {
+    if (!this.signer) {
+      throw new Error('No signer configured. Call setSigner() first.');
+    }
+    const message = new TextEncoder().encode(POLICY_MASTER_SEED_SIGN_MESSAGE);
+    const [signature, pubkey] = await Promise.all([
+      this.signer.signMessage(message),
+      this.signer.getPublicKey(),
+    ]);
+    return derivePolicyMasterSeedFromSignature(pubkey.toBytes(), signature);
+  }
+
   /**
    * Build, sign, and optionally send a transaction based on mode
    */
@@ -425,9 +444,8 @@ export class HydentityClient<T = SolanaTransactionSignature> {
       throw new Error(`Insufficient vault balance: ${balance.sol} < ${amount}`);
     }
 
-    // Create policy engine for this claim
-    const signer = await this.getSignerPublicKey();
-    const masterSeed = new Uint8Array(32); // TODO: Derive from signer
+    // Create policy engine for this claim (wallet-specific entropy via message sign)
+    const masterSeed = await this.derivePolicyMasterSeed();
     const policyEngine = new PolicyEngine(masterSeed, policy.policyNonce);
 
     // Generate execution plan
diff --git a/packages/hydentity-sdk/src/constants.ts b/packages/hydentity-sdk/src/constants.ts
index 3a3ffa0..cf8507a 100644
--- a/packages/hydentity-sdk/src/constants.ts
+++ b/packages/hydentity-sdk/src/constants.ts
@@ -42,6 +42,16 @@ export const DUST_THRESHOLD_LAMPORTS = 10_000n; // 0.00001 SOL
 export const KMAC_DOMAIN_RANDOM_SEED = 'Hydentity - Random Seed';
 export const KMAC_DOMAIN_SPLIT_SEED = 'Hydentity - Split Seed';
 export const KMAC_DOMAIN_DELAY_SEED = 'Hydentity - Delay Seed';
+/** KMAC domain for hashing wallet proof into policy execution seed */
+export const KMAC_DOMAIN_POLICY_MASTER_SEED = 'Hydentity - Policy Master Seed';
+
+/**
+ * Message bytes users sign to derive per-wallet policy execution entropy for
+ * split and delay plans. Does not authorize transfers by itself.
+ */
+export const POLICY_MASTER_SEED_SIGN_MESSAGE =
+  'Sign to derive Hydentity private withdrawal split entropy. ' +
+  'This does not grant any transfer.';
 
 /**
  * SNS TLD key for .sol domains
diff --git a/packages/hydentity-sdk/src/utils/randomness.test.ts b/packages/hydentity-sdk/src/utils/randomness.test.ts
new file mode 100644
index 0000000..19569ed
--- /dev/null
+++ b/packages/hydentity-sdk/src/utils/randomness.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it } from 'vitest';
+import { derivePolicyMasterSeedFromSignature } from './randomness';
+
+describe('derivePolicyMasterSeedFromSignature', () => {
+  it('rejects wrong pubkey length', () => {
+    expect(() =>
+      derivePolicyMasterSeedFromSignature(new Uint8Array(31), new Uint8Array(64))
+    ).toThrow('32 bytes');
+  });
+
+  it('rejects wrong signature length', () => {
+    expect(() =>
+      derivePolicyMasterSeedFromSignature(new Uint8Array(32), new Uint8Array(63))
+    ).toThrow('64 bytes');
+  });
+
+  it('is deterministic for the same proof', () => {
+    const pk = new Uint8Array(32).fill(7);
+    const sig = new Uint8Array(64).fill(3);
+    const a = derivePolicyMasterSeedFromSignature(pk, sig);
+    const b = derivePolicyMasterSeedFromSignature(pk, sig);
+    expect(a).toEqual(b);
+    expect(a.length).toBe(32);
+  });
+
+  it('differs when signature bytes change', () => {
+    const pk = new Uint8Array(32).fill(1);
+    const sig1 = new Uint8Array(64).fill(2);
+    const sig2 = new Uint8Array(64).fill(9);
+    const s1 = derivePolicyMasterSeedFromSignature(pk, sig1);
+    const s2 = derivePolicyMasterSeedFromSignature(pk, sig2);
+    expect(Array.from(s1).join()).not.toBe(Array.from(s2).join());
+  });
+});
diff --git a/packages/hydentity-sdk/src/utils/randomness.ts b/packages/hydentity-sdk/src/utils/randomness.ts
index 16abc3b..ad92fda 100644
--- a/packages/hydentity-sdk/src/utils/randomness.ts
+++ b/packages/hydentity-sdk/src/utils/randomness.ts
@@ -3,6 +3,7 @@ import {
   KMAC_DOMAIN_RANDOM_SEED,
   KMAC_DOMAIN_SPLIT_SEED,
   KMAC_DOMAIN_DELAY_SEED,
+  KMAC_DOMAIN_POLICY_MASTER_SEED,
   DUST_THRESHOLD_LAMPORTS,
 } from '../constants';
 import type { Amount, U128 } from '../types/common';
@@ -49,6 +50,30 @@ export function deriveRandomSeed(masterSeed: Uint8Array, nonce: bigint): Uint8Ar
   );
 }
 
+/**
+ * Derive 32-byte policy master seed from a wallet message-signing proof.
+ * Callers must pass the Ed25519 signature of POLICY_MASTER_SEED_SIGN_MESSAGE.
+ */
+export function derivePolicyMasterSeedFromSignature(
+  walletPublicKey32: Uint8Array,
+  messageSignature64: Uint8Array
+): Uint8Array {
+  if (walletPublicKey32.length !== 32) {
+    throw new Error('wallet public key must be 32 bytes');
+  }
+  if (messageSignature64.length !== 64) {
+    throw new Error('Ed25519 signature must be 64 bytes');
+  }
+  const input = new Uint8Array(32 + 64);
+  input.set(walletPublicKey32, 0);
+  input.set(messageSignature64, 32);
+  return kmac256(
+    new TextEncoder().encode(KMAC_DOMAIN_POLICY_MASTER_SEED),
+    input,
+    { dkLen: 32 }
+  );
+}
+
 /**
  * Generate a deterministic random value from seed and index
  *