diff --git a/modules/passkey-crypto/package.json b/modules/passkey-crypto/package.json
index 1c3beb216b..d87804a456 100644
--- a/modules/passkey-crypto/package.json
+++ b/modules/passkey-crypto/package.json
@@ -35,8 +35,7 @@
   },
   "dependencies": {
     "@bitgo/public-types": "6.1.0",
-    "@bitgo/sdk-core": "^36.42.0",
-    "@bitgo/sjcl": "^1.1.0"
+    "@bitgo/sdk-core": "^36.44.0"
   },
   "devDependencies": {
     "@types/node": "^18.0.0"
diff --git a/modules/passkey-crypto/src/attachPasskeyToWallet.ts b/modules/passkey-crypto/src/attachPasskeyToWallet.ts
new file mode 100644
index 0000000000..575828f7b9
--- /dev/null
+++ b/modules/passkey-crypto/src/attachPasskeyToWallet.ts
@@ -0,0 +1,88 @@
+import { BitGoBase, Keychain } from '@bitgo/sdk-core';
+import { deriveEnterpriseSalt } from './deriveEnterpriseSalt';
+import { derivePassword } from './derivePassword';
+import { WebAuthnOtpDevice, WebAuthnProvider } from './webAuthnTypes';
+
+export async function attachPasskeyToWallet(params: {
+  bitgo: BitGoBase;
+  coin: string;
+  walletId: string;
+  device: WebAuthnOtpDevice;
+  existingPassphrase: string;
+  provider: WebAuthnProvider;
+}): Promise<Keychain> {
+  const { bitgo, coin, walletId, device, existingPassphrase, provider } = params;
+
+  // Throw early if PRF extension is not supported
+  if (!device.prfSalt) {
+    throw new Error('PRF extension not supported by this device. Please use a different passkey.');
+  }
+
+  const baseCoin = bitgo.coin(coin);
+
+  // Fetch wallet and validate it is a hot wallet
+  const wallet = await baseCoin.wallets().get({ id: walletId });
+
+  if (wallet.type() !== 'hot') {
+    throw new Error(`Wallet ${walletId} is not a hot wallet. Only hot wallets support passkey attachment.`);
+  }
+
+  const walletData = wallet.toJSON();
+  const enterpriseId = walletData.enterprise;
+  if (!enterpriseId) {
+    throw new Error(`Wallet ${walletId} has no enterprise.`);
+  }
+
+  // Fetch the user keychain — iterates keys until it finds one with encryptedPrv
+  const keychain = await wallet.getEncryptedUserKeychain();
+  const keychainId = keychain.id;
+
+  // Derive enterprise-scoped salt
+  const enterpriseSalt = deriveEnterpriseSalt(device.prfSalt, enterpriseId);
+
+  // Decrypt private key with existing passphrase
+  const privateKey = bitgo.decrypt({ password: existingPassphrase, input: keychain.encryptedPrv });
+
+  // Decode credentialId from base64url to ArrayBuffer for allowCredentials.
+  // The WebAuthn spec requires allowCredentials to be non-empty when using evalByCredential,
+  // and each entry must correspond to a key in the evalByCredential map.
+  const credentialIdBuffer = Buffer.from(device.credentialId.replace(/-/g, '+').replace(/_/g, '/'), 'base64').buffer;
+
+  // PRF assertion — evalByCredential maps this device's credentialId to its enterprise salt
+  const authResult = await provider.get({
+    publicKey: {
+      allowCredentials: [{ type: 'public-key', id: credentialIdBuffer }],
+    } as PublicKeyCredentialRequestOptions,
+    evalByCredential: { [device.credentialId]: enterpriseSalt },
+  });
+
+  if (!authResult.prfResult) {
+    throw new Error('PRF assertion did not return a result.');
+  }
+
+  // Derive password from PRF output and re-encrypt
+  const prfPassword = derivePassword(authResult.prfResult);
+  const encryptedPrv = bitgo.encrypt({ password: prfPassword, input: privateKey });
+
+  // Convert enterpriseSalt from hex to base64url (URL-safe, no padding)
+  // as required by the server's prfSalt validation.
+  const prfSaltBase64url = Buffer.from(enterpriseSalt, 'hex')
+    .toString('base64')
+    .replace(/\+/g, '-')
+    .replace(/\//g, '_')
+    .replace(/=+$/, '');
+
+  // PUT webauthnInfo to keychain endpoint
+  const updatedKeychain = await bitgo
+    .put(bitgo.url(`/${coin}/key/${keychainId}`, 2))
+    .send({
+      webauthnInfo: {
+        prfSalt: prfSaltBase64url,
+        otpDeviceId: device.id,
+        encryptedPrv,
+      },
+    })
+    .result();
+
+  return updatedKeychain as Keychain;
+}
diff --git a/modules/passkey-crypto/src/deriveEnterpriseSalt.ts b/modules/passkey-crypto/src/deriveEnterpriseSalt.ts
index 688c3e9822..caef1d40fe 100644
--- a/modules/passkey-crypto/src/deriveEnterpriseSalt.ts
+++ b/modules/passkey-crypto/src/deriveEnterpriseSalt.ts
@@ -1,11 +1,4 @@
-import * as sjcl from '@bitgo/sjcl';
-import type { SjclCodecs, SjclHashes, SjclMisc } from '@bitgo/sjcl';
-
-type SjclType = {
-  hash: SjclHashes;
-  codec: SjclCodecs;
-  misc: SjclMisc;
-};
+import { createHmac } from 'crypto';
 
 /**
  * Derives an enterprise-scoped PRF salt to prevent cross-enterprise key reuse.
@@ -15,16 +8,9 @@ type SjclType = {
  *
  * @param baseSalt - Server-provided base64url-encoded PRF salt
  * @param enterpriseId - Enterprise identifier
- * @returns Base64-encoded HMAC-SHA256 digest
+ * @returns Hex-encoded HMAC-SHA256 digest
  */
 export function deriveEnterpriseSalt(baseSalt: string, enterpriseId: string): string {
-  const { misc, codec, hash } = sjcl as unknown as SjclType;
-
-  const keyBits = codec.base64url.toBits(baseSalt);
-  const dataBits = codec.utf8String.toBits(enterpriseId);
-
-  const hmacInstance = new misc.hmac(keyBits, hash.sha256);
-  const resultBits = hmacInstance.mac(dataBits);
-
-  return codec.base64.fromBits(resultBits);
+  const keyBytes = Buffer.from(baseSalt.replace(/-/g, '+').replace(/_/g, '/'), 'base64');
+  return createHmac('sha256', keyBytes).update(enterpriseId).digest('hex');
 }
diff --git a/modules/passkey-crypto/test/unit/attachPasskeyToWallet.test.ts b/modules/passkey-crypto/test/unit/attachPasskeyToWallet.test.ts
new file mode 100644
index 0000000000..222515cfaa
--- /dev/null
+++ b/modules/passkey-crypto/test/unit/attachPasskeyToWallet.test.ts
@@ -0,0 +1,247 @@
+import * as assert from 'assert';
+import * as sinon from 'sinon';
+import { attachPasskeyToWallet } from '../../src/attachPasskeyToWallet';
+import { WebAuthnOtpDevice, PasskeyAuthResult, WebAuthnProvider } from '../../src/webAuthnTypes';
+
+describe('attachPasskeyToWallet', function () {
+  const coin = 'tbtc';
+  const walletId = 'wallet-abc123';
+  const keychainId = 'key-user-id';
+  const enterpriseId = 'enterprise-xyz';
+  const encryptedPrv = 'encrypted-prv-string';
+  const decryptedPrv = 'xprv-decrypted';
+  const existingPassphrase = 'correct-passphrase';
+  const reEncryptedPrv = 're-encrypted-prv';
+
+  const prfResultBuffer = new Uint8Array([0x1e, 0x5c, 0xb4, 0x78]).buffer;
+
+  const device: WebAuthnOtpDevice = {
+    id: 'mongo-object-id-123',
+    credentialId: 'cred-id-456',
+    prfSalt: 'ZqJ64M2dL65zn2-Jxd58SMN2ILc9QjbCFxUTGHd_LC8',
+    isPasskey: true,
+  };
+
+  const mockAuthResult: PasskeyAuthResult = {
+    prfResult: prfResultBuffer,
+    credentialId: 'cred-id-456',
+    otpCode: '123456',
+  };
+
+  const updatedKeychain = {
+    id: keychainId,
+    pub: 'xpub-123',
+    type: 'independent' as const,
+    encryptedPrv,
+  };
+
+  let mockWallet: {
+    type: sinon.SinonStub;
+    toJSON: sinon.SinonStub;
+    getEncryptedUserKeychain: sinon.SinonStub;
+  };
+
+  let mockWallets: {
+    get: sinon.SinonStub;
+  };
+
+  let mockBaseCoin: {
+    wallets: sinon.SinonStub;
+  };
+
+  let mockBitGo: {
+    url: sinon.SinonStub;
+    coin: sinon.SinonStub;
+    put: sinon.SinonStub;
+    decrypt: sinon.SinonStub;
+    encrypt: sinon.SinonStub;
+  };
+
+  let mockProvider: {
+    create: sinon.SinonStub;
+    get: sinon.SinonStub;
+  };
+
+  beforeEach(function () {
+    mockWallet = {
+      type: sinon.stub().returns('hot'),
+      toJSON: sinon.stub().returns({ enterprise: enterpriseId }),
+      getEncryptedUserKeychain: sinon.stub().resolves({ id: keychainId, encryptedPrv }),
+    };
+
+    mockWallets = {
+      get: sinon.stub().resolves(mockWallet),
+    };
+
+    mockBaseCoin = {
+      wallets: sinon.stub().returns(mockWallets),
+    };
+
+    mockBitGo = {
+      url: sinon
+        .stub<[path: string, version?: number], string>()
+        .callsFake((path, version) => `/api/v${version ?? 1}${path}`),
+      coin: sinon.stub().returns(mockBaseCoin),
+      put: sinon.stub(),
+      decrypt: sinon.stub(),
+      encrypt: sinon.stub(),
+    };
+
+    mockProvider = {
+      create: sinon.stub(),
+      get: sinon.stub(),
+    };
+
+    mockBitGo.decrypt.returns(decryptedPrv);
+    mockBitGo.encrypt.returns(reEncryptedPrv);
+
+    const putSendStub = sinon.stub().returns({ result: sinon.stub().resolves(updatedKeychain) });
+    mockBitGo.put.returns({ send: putSendStub });
+
+    mockProvider.get.resolves(mockAuthResult);
+  });
+
+  afterEach(function () {
+    sinon.restore();
+  });
+
+  async function callAttach(overrides?: Partial<Parameters<typeof attachPasskeyToWallet>[0]>) {
+    return attachPasskeyToWallet({
+      bitgo: mockBitGo as unknown as Parameters<typeof attachPasskeyToWallet>[0]['bitgo'],
+      coin,
+      walletId,
+      device,
+      existingPassphrase,
+      provider: mockProvider as unknown as WebAuthnProvider,
+      ...overrides,
+    });
+  }
+
+  it('should attach a passkey and return the updated keychain', async function () {
+    const result = await callAttach();
+
+    sinon.assert.calledWith(mockBitGo.coin, coin);
+    sinon.assert.calledWith(mockWallets.get, { id: walletId });
+    sinon.assert.calledOnce(mockWallet.type);
+    sinon.assert.calledOnce(mockWallet.getEncryptedUserKeychain);
+    sinon.assert.calledOnce(mockBitGo.decrypt);
+    sinon.assert.calledWithExactly(mockBitGo.decrypt, { password: existingPassphrase, input: encryptedPrv });
+
+    // provider.get called with evalByCredential keyed on device.credentialId
+    sinon.assert.calledOnce(mockProvider.get);
+    const getArgs = mockProvider.get.firstCall.args[0];
+    assert.ok(getArgs.evalByCredential);
+    assert.strictEqual(typeof getArgs.evalByCredential[device.credentialId], 'string');
+
+    // allowCredentials must be populated with the credential ID as an ArrayBuffer
+    assert.ok(Array.isArray(getArgs.publicKey.allowCredentials));
+    assert.strictEqual(getArgs.publicKey.allowCredentials.length, 1);
+    assert.strictEqual(getArgs.publicKey.allowCredentials[0].type, 'public-key');
+    assert.ok(getArgs.publicKey.allowCredentials[0].id instanceof ArrayBuffer);
+
+    // PUT called with correct shape
+    sinon.assert.calledOnce(mockBitGo.put);
+    sinon.assert.calledWith(mockBitGo.put, `/api/v2/${coin}/key/${keychainId}`);
+    const sendStub = mockBitGo.put.firstCall.returnValue.send;
+    sinon.assert.calledOnce(sendStub);
+    const putBody = sendStub.firstCall.args[0];
+    assert.ok(putBody.webauthnInfo);
+    assert.strictEqual(putBody.webauthnInfo.otpDeviceId, device.id);
+    // prfSalt must be base64url (URL-safe, no padding) as required by server validation
+    assert.match(putBody.webauthnInfo.prfSalt, /^[A-Za-z0-9\-_]+$/);
+    assert.strictEqual(typeof putBody.webauthnInfo.encryptedPrv, 'string');
+
+    assert.strictEqual(result.id, keychainId);
+  });
+
+  it('should decode credentialId containing base64url-specific characters (- and _)', async function () {
+    const deviceWithUrlChars: WebAuthnOtpDevice = {
+      ...device,
+      credentialId: 'abc-def_ghi+jkl',
+    };
+
+    const result = await callAttach({ device: deviceWithUrlChars });
+    assert.ok(result);
+
+    const getArgs = mockProvider.get.firstCall.args[0];
+    assert.ok(getArgs.publicKey.allowCredentials[0].id instanceof ArrayBuffer);
+  });
+
+  it('should throw if device.prfSalt is undefined', async function () {
+    const deviceNoPrf: WebAuthnOtpDevice = { ...device, prfSalt: undefined };
+
+    await assert.rejects(
+      () => callAttach({ device: deviceNoPrf }),
+      (err: Error) => {
+        assert.strictEqual(err.message, 'PRF extension not supported by this device. Please use a different passkey.');
+        return true;
+      }
+    );
+
+    sinon.assert.notCalled(mockBitGo.coin);
+    sinon.assert.notCalled(mockBitGo.put);
+  });
+
+  it('should throw if wallet is not a hot wallet', async function () {
+    mockWallet.type.returns('cold');
+
+    await assert.rejects(
+      () => callAttach(),
+      (err: Error) => {
+        assert.ok(err.message.includes('not a hot wallet'));
+        return true;
+      }
+    );
+
+    sinon.assert.notCalled(mockBitGo.put);
+  });
+
+  it('should throw if wallet has no enterprise', async function () {
+    mockWallet.toJSON.returns({ enterprise: undefined });
+
+    await assert.rejects(
+      () => callAttach(),
+      (err: Error) => {
+        assert.ok(err.message.includes('has no enterprise'));
+        return true;
+      }
+    );
+  });
+
+  it('should throw if PRF assertion returns no result', async function () {
+    mockProvider.get.resolves({ ...mockAuthResult, prfResult: undefined });
+
+    await assert.rejects(
+      () => callAttach(),
+      (err: Error) => {
+        assert.ok(err.message.includes('PRF assertion did not return a result'));
+        return true;
+      }
+    );
+
+    sinon.assert.notCalled(mockBitGo.put);
+  });
+
+  it('should propagate decrypt errors', async function () {
+    mockBitGo.decrypt.throws(new Error('decryption failed'));
+
+    await assert.rejects(
+      () => callAttach(),
+      (err: Error) => {
+        assert.ok(err.message.includes('decryption failed'));
+        return true;
+      }
+    );
+
+    sinon.assert.notCalled(mockBitGo.put);
+  });
+
+  it('should use device.credentialId as the key in evalByCredential', async function () {
+    await callAttach();
+
+    const getArgs = mockProvider.get.firstCall.args[0];
+    const evalKeys = Object.keys(getArgs.evalByCredential);
+    assert.strictEqual(evalKeys.length, 1);
+    assert.strictEqual(evalKeys[0], device.credentialId);
+  });
+});
diff --git a/modules/passkey-crypto/test/unit/deriveEnterpriseSalt.test.ts b/modules/passkey-crypto/test/unit/deriveEnterpriseSalt.test.ts
index 7d1c7d49d2..d9eaab111f 100644
--- a/modules/passkey-crypto/test/unit/deriveEnterpriseSalt.test.ts
+++ b/modules/passkey-crypto/test/unit/deriveEnterpriseSalt.test.ts
@@ -5,7 +5,7 @@ import { deriveEnterpriseSalt } from '../../src';
 const REAL_FIXTURE = {
   basePrfSalt: 'ZqJ64M2dL65zn2-Jxd58SMN2ILc9QjbCFxUTGHd_LC8',
   enterpriseId: '69c2aea1a3d7bc07f7f775c0ca86b0ec',
-  expectedDerivedSalt: 'oiasOqzkuyuEz/8043+3IXYghSu3LV4N/a1MLIRzmU8=',
+  expectedDerivedSalt: 'a226ac3aace4bb2b84cfff34e37fb7217620852bb72d5e0dfdad4c2c8473994f',
 };
 
 describe('deriveEnterpriseSalt', function () {
@@ -37,10 +37,10 @@ describe('deriveEnterpriseSalt', function () {
     assert.notStrictEqual(saltA, saltB);
   });
 
-  it('returns a non-empty base64 string', function () {
+  it('returns a non-empty hex string', function () {
     const result = deriveEnterpriseSalt(REAL_FIXTURE.basePrfSalt, REAL_FIXTURE.enterpriseId);
     assert.strictEqual(typeof result, 'string');
     assert.ok(result.length > 0);
-    assert.match(result, /^[A-Za-z0-9+/]+=*$/);
+    assert.match(result, /^[0-9a-f]{64}$/);
   });
 });