diff --git a/keyserver/src/responders/siwe-nonce-responders.js b/keyserver/src/responders/siwe-nonce-responders.js
--- a/keyserver/src/responders/siwe-nonce-responders.js
+++ b/keyserver/src/responders/siwe-nonce-responders.js
@@ -1,7 +1,27 @@
 // @flow
 
-async function siweNonceResponder(): Promise<string> {
-  return 'UNIMPLEMENTED';
+import { generateNonce } from 'siwe';
+import t from 'tcomb';
+
+import type {
+  SIWENonceRequest,
+  SIWENonceResponse,
+} from 'lib/types/siwe-types.js';
+import { tShape } from 'lib/utils/validation-utils';
+
+import type { Viewer } from '../session/viewer.js';
+import { validateInput } from '../utils/validation-utils.js';
+
+const siweNonceRequestInputValidator = tShape({
+  walletAddress: t.String,
+});
+async function siweNonceResponder(
+  viewer: Viewer,
+  input: any,
+): Promise<SIWENonceResponse> {
+  const request: SIWENonceRequest = input;
+  await validateInput(viewer, siweNonceRequestInputValidator, request);
+  return { nonce: generateNonce() };
 }
 
 export { siweNonceResponder };
diff --git a/lib/types/siwe-types.js b/lib/types/siwe-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/siwe-types.js
@@ -0,0 +1,9 @@
+// @flow
+
+export type SIWENonceRequest = {
+  +walletAddress: string,
+};
+
+export type SIWENonceResponse = {
+  +nonce: string,
+};