diff --git a/modules/sdk-core/src/bitgo/index.ts b/modules/sdk-core/src/bitgo/index.ts
index c320eee454..df9ecb83c5 100644
--- a/modules/sdk-core/src/bitgo/index.ts
+++ b/modules/sdk-core/src/bitgo/index.ts
@@ -20,6 +20,7 @@ export * from './market';
 export * from './pendingApproval';
 export { WalletProofs } from './proofs';
 export * from './recovery';
+export * from './passkey';
 export * from './staking';
 export * from './trading';
 export * from './tss';
diff --git a/modules/sdk-core/src/bitgo/passkey/index.ts b/modules/sdk-core/src/bitgo/passkey/index.ts
new file mode 100644
index 0000000000..5d3fd68176
--- /dev/null
+++ b/modules/sdk-core/src/bitgo/passkey/index.ts
@@ -0,0 +1,2 @@
+export { WebAuthnOtpDevice, PasskeyAuthResult, WebAuthnProvider } from './types';
+export { buildEvalByCredential, matchDeviceByCredentialId } from './prfHelpers';
diff --git a/modules/sdk-core/src/bitgo/passkey/prfHelpers.ts b/modules/sdk-core/src/bitgo/passkey/prfHelpers.ts
new file mode 100644
index 0000000000..a0117bd351
--- /dev/null
+++ b/modules/sdk-core/src/bitgo/passkey/prfHelpers.ts
@@ -0,0 +1,38 @@
+import { KeychainWebauthnDevice } from '../keychain/iKeychains';
+
+/**
+ * Builds the `evalByCredential` map passed to `WebAuthnProvider.get()`.
+ * Maps each device's credID to its prfSalt so the authenticator can
+ * evaluate the PRF with the correct salt for whichever credential it selects.
+ *
+ * Mirrors retail's buildEvalByCredentialFromKeychain — takes KeychainWebauthnDevice[]
+ * directly so credID is read from authenticatorInfo where it actually lives.
+ *
+ * @param devices - webauthnDevices from the wallet keychain
+ * @returns a map of { [credID]: prfSalt }
+ */
+export function buildEvalByCredential(devices: KeychainWebauthnDevice[]): Record<string, string> {
+  return Object.fromEntries(devices.map((d) => [d.authenticatorInfo.credID, d.prfSalt]));
+}
+
+/**
+ * Finds the KeychainWebauthnDevice whose credID matches the credential ID
+ * returned by the WebAuthn assertion.
+ *
+ * @param devices - webauthnDevices from the wallet keychain
+ * @param credentialId - base64url credential ID from the WebAuthn assertion
+ * @throws if no device matches
+ */
+export function matchDeviceByCredentialId(
+  devices: KeychainWebauthnDevice[],
+  credentialId: string
+): KeychainWebauthnDevice {
+  const device = devices.find((d) => d.authenticatorInfo.credID === credentialId);
+  if (!device) {
+    throw new Error(
+      `No passkey device found matching credential ID "${credentialId}". ` +
+        `Known credential IDs: [${devices.map((d) => d.authenticatorInfo.credID).join(', ')}]`
+    );
+  }
+  return device;
+}
diff --git a/modules/sdk-core/src/bitgo/passkey/types.ts b/modules/sdk-core/src/bitgo/passkey/types.ts
new file mode 100644
index 0000000000..b50b3dcfbb
--- /dev/null
+++ b/modules/sdk-core/src/bitgo/passkey/types.ts
@@ -0,0 +1,28 @@
+export interface WebAuthnOtpDevice {
+  /** MongoDB ObjectId — used for deletion API calls */
+  otpDeviceId: string;
+  /** base64url WebAuthn credential ID */
+  credID: string;
+  /** WebAuthn attestation format */
+  fmt: 'none' | 'packed' | 'fido-u2f';
+  /** Base64-encoded public key from the authenticator */
+  publicKey: string;
+  /** base64url-encoded salt from the server — optional */
+  prfSalt?: string;
+  /** SJCL-encrypted private key (present once passkey is attached to a wallet keychain) */
+  encryptedPrv?: string;
+}
+
+export interface PasskeyAuthResult {
+  /** Raw PRF output — undefined if the authenticator does not support PRF */
+  prfResult: ArrayBuffer | undefined;
+  /** base64url credential ID returned by the authenticator — matches KeychainWebauthnDevice.authenticatorInfo.credID */
+  credentialId: string;
+  /** JSON-stringified WebAuthn assertion — pass to sdk.unlock({ otp: otpCode }) */
+  otpCode: string;
+}
+
+export interface WebAuthnProvider {
+  create(options: PublicKeyCredentialCreationOptions): Promise<PublicKeyCredential | null>;
+  get(options: PublicKeyCredentialRequestOptions): Promise<PublicKeyCredential | null>;
+}
diff --git a/modules/sdk-core/test/unit/bitgo/passkey/prfHelpers.test.ts b/modules/sdk-core/test/unit/bitgo/passkey/prfHelpers.test.ts
new file mode 100644
index 0000000000..4094fb1eea
--- /dev/null
+++ b/modules/sdk-core/test/unit/bitgo/passkey/prfHelpers.test.ts
@@ -0,0 +1,64 @@
+import * as assert from 'assert';
+import { buildEvalByCredential, matchDeviceByCredentialId } from '../../../../src/bitgo/passkey/prfHelpers';
+import { KeychainWebauthnDevice } from '../../../../src/bitgo/keychain/iKeychains';
+
+const device1: KeychainWebauthnDevice = {
+  otpDeviceId: 'oid-1',
+  authenticatorInfo: { credID: 'cred-aaa', fmt: 'none', publicKey: 'pk-1' },
+  prfSalt: 'salt-aaa',
+  encryptedPrv: 'enc-prv-1',
+};
+
+const device2: KeychainWebauthnDevice = {
+  otpDeviceId: 'oid-2',
+  authenticatorInfo: { credID: 'cred-bbb', fmt: 'none', publicKey: 'pk-2' },
+  prfSalt: 'salt-bbb',
+  encryptedPrv: 'enc-prv-2',
+};
+
+describe('buildEvalByCredential', function () {
+  it('maps each device authenticatorInfo.credID to its prfSalt', function () {
+    const result = buildEvalByCredential([device1, device2]);
+    assert.deepStrictEqual(result, {
+      'cred-aaa': 'salt-aaa',
+      'cred-bbb': 'salt-bbb',
+    });
+  });
+
+  it('returns an empty object for an empty device list', function () {
+    assert.deepStrictEqual(buildEvalByCredential([]), {});
+  });
+
+  it('returns a single-entry map for one device', function () {
+    const result = buildEvalByCredential([device1]);
+    assert.deepStrictEqual(result, { 'cred-aaa': 'salt-aaa' });
+  });
+});
+
+describe('matchDeviceByCredentialId', function () {
+  it('returns the matching device', function () {
+    const result = matchDeviceByCredentialId([device1, device2], 'cred-bbb');
+    assert.strictEqual(result, device2);
+  });
+
+  it('returns the first device when it matches', function () {
+    const result = matchDeviceByCredentialId([device1, device2], 'cred-aaa');
+    assert.strictEqual(result, device1);
+  });
+
+  it('throws a descriptive error when no device matches', function () {
+    assert.throws(
+      () => matchDeviceByCredentialId([device1, device2], 'cred-unknown'),
+      (err: Error) => {
+        assert.ok(err.message.includes('cred-unknown'));
+        assert.ok(err.message.includes('cred-aaa'));
+        assert.ok(err.message.includes('cred-bbb'));
+        return true;
+      }
+    );
+  });
+
+  it('throws when the device list is empty', function () {
+    assert.throws(() => matchDeviceByCredentialId([], 'cred-aaa'), Error);
+  });
+});