diff --git a/src/lib/server/db/client.ts b/src/lib/server/db/client.ts
index cb873c7..373357a 100644
--- a/src/lib/server/db/client.ts
+++ b/src/lib/server/db/client.ts
@@ -178,7 +178,7 @@ export const registerUserClientChallenge = async (
   allowedIp: string,
   expiresAt: Date,
 ) => {
-  await db
+  const { id } = await db
     .insertInto("user_client_challenge")
     .values({
       user_id: userId,
@@ -187,19 +187,25 @@ export const registerUserClientChallenge = async (
       allowed_ip: allowedIp,
       expires_at: expiresAt,
     })
-    .execute();
+    .returning("id")
+    .executeTakeFirstOrThrow();
+  return { id };
 };
 
-export const consumeUserClientChallenge = async (userId: number, answer: string, ip: string) => {
+export const consumeUserClientChallenge = async (
+  challengeId: number,
+  userId: number,
+  ip: string,
+) => {
   const challenge = await db
     .deleteFrom("user_client_challenge")
+    .where("id", "=", challengeId)
     .where("user_id", "=", userId)
-    .where("answer", "=", answer)
     .where("allowed_ip", "=", ip)
     .where("expires_at", ">", new Date())
-    .returning("client_id")
+    .returning(["client_id", "answer"])
     .executeTakeFirst();
-  return challenge ? { clientId: challenge.client_id } : null;
+  return challenge ? { clientId: challenge.client_id, answer: challenge.answer } : null;
 };
 
 export const cleanupExpiredUserClientChallenges = async () => {
diff --git a/src/lib/server/db/session.ts b/src/lib/server/db/session.ts
index 727f795..653c20c 100644
--- a/src/lib/server/db/session.ts
+++ b/src/lib/server/db/session.ts
@@ -94,7 +94,7 @@ export const registerSessionUpgradeChallenge = async (
   expiresAt: Date,
 ) => {
   try {
-    await db
+    const { id } = await db
       .insertInto("session_upgrade_challenge")
       .values({
         session_id: sessionId,
@@ -103,7 +103,9 @@ export const registerSessionUpgradeChallenge = async (
         allowed_ip: allowedIp,
         expires_at: expiresAt,
       })
-      .execute();
+      .returning("id")
+      .executeTakeFirstOrThrow();
+    return { id };
   } catch (e) {
     if (e instanceof pg.DatabaseError && e.code === "23505") {
       throw new IntegrityError("Challenge already registered");
@@ -113,19 +115,19 @@ export const registerSessionUpgradeChallenge = async (
 };
 
 export const consumeSessionUpgradeChallenge = async (
+  challengeId: number,
   sessionId: string,
-  answer: string,
   ip: string,
 ) => {
   const challenge = await db
     .deleteFrom("session_upgrade_challenge")
+    .where("id", "=", challengeId)
     .where("session_id", "=", sessionId)
-    .where("answer", "=", answer)
     .where("allowed_ip", "=", ip)
     .where("expires_at", ">", new Date())
-    .returning("client_id")
+    .returning(["client_id", "answer"])
     .executeTakeFirst();
-  return challenge ? { clientId: challenge.client_id } : null;
+  return challenge ? { clientId: challenge.client_id, answer: challenge.answer } : null;
 };
 
 export const cleanupExpiredSessionUpgradeChallenges = async () => {
diff --git a/src/lib/server/schemas/auth.ts b/src/lib/server/schemas/auth.ts
index e3d6264..e90b209 100644
--- a/src/lib/server/schemas/auth.ts
+++ b/src/lib/server/schemas/auth.ts
@@ -19,12 +19,13 @@ export const sessionUpgradeRequest = z.object({
 export type SessionUpgradeRequest = z.infer<typeof sessionUpgradeRequest>;
 
 export const sessionUpgradeResponse = z.object({
+  id: z.number().int().positive(),
   challenge: z.string().base64().nonempty(),
 });
 export type SessionUpgradeResponse = z.infer<typeof sessionUpgradeResponse>;
 
 export const sessionUpgradeVerifyRequest = z.object({
-  answer: z.string().base64().nonempty(),
+  id: z.number().int().positive(),
   answerSig: z.string().base64().nonempty(),
 });
 export type SessionUpgradeVerifyRequest = z.infer<typeof sessionUpgradeVerifyRequest>;
diff --git a/src/lib/server/schemas/client.ts b/src/lib/server/schemas/client.ts
index 53cbb88..df15e39 100644
--- a/src/lib/server/schemas/client.ts
+++ b/src/lib/server/schemas/client.ts
@@ -17,12 +17,13 @@ export const clientRegisterRequest = z.object({
 export type ClientRegisterRequest = z.infer<typeof clientRegisterRequest>;
 
 export const clientRegisterResponse = z.object({
+  id: z.number().int().positive(),
   challenge: z.string().base64().nonempty(),
 });
 export type ClientRegisterResponse = z.infer<typeof clientRegisterResponse>;
 
 export const clientRegisterVerifyRequest = z.object({
-  answer: z.string().base64().nonempty(),
+  id: z.number().int().positive(),
   answerSig: z.string().base64().nonempty(),
 });
 export type ClientRegisterVerifyRequest = z.infer<typeof clientRegisterVerifyRequest>;
diff --git a/src/lib/server/services/auth.ts b/src/lib/server/services/auth.ts
index 81f0333..2eb496c 100644
--- a/src/lib/server/services/auth.ts
+++ b/src/lib/server/services/auth.ts
@@ -81,7 +81,7 @@ export const createSessionUpgradeChallenge = async (
   }
 
   const { answer, challenge } = await generateChallenge(32, encPubKey);
-  await registerSessionUpgradeChallenge(
+  const { id } = await registerSessionUpgradeChallenge(
     sessionId,
     client.id,
     answer.toString("base64"),
@@ -89,16 +89,16 @@ export const createSessionUpgradeChallenge = async (
     new Date(Date.now() + env.challenge.sessionUpgradeExp),
   );
 
-  return { challenge: challenge.toString("base64") };
+  return { id, challenge: challenge.toString("base64") };
 };
 
 export const verifySessionUpgradeChallenge = async (
   sessionId: string,
   ip: string,
-  answer: string,
+  challengeId: number,
   answerSig: string,
 ) => {
-  const challenge = await consumeSessionUpgradeChallenge(sessionId, answer, ip);
+  const challenge = await consumeSessionUpgradeChallenge(challengeId, sessionId, ip);
   if (!challenge) {
     error(403, "Invalid challenge answer");
   }
@@ -106,7 +106,9 @@ export const verifySessionUpgradeChallenge = async (
   const client = await getClient(challenge.clientId);
   if (!client) {
     error(500, "Invalid challenge answer");
-  } else if (!verifySignature(Buffer.from(answer, "base64"), answerSig, client.sigPubKey)) {
+  } else if (
+    !verifySignature(Buffer.from(challenge.answer, "base64"), answerSig, client.sigPubKey)
+  ) {
     error(403, "Invalid challenge answer signature");
   }
 
diff --git a/src/lib/server/services/client.ts b/src/lib/server/services/client.ts
index ee1b5b3..811e58c 100644
--- a/src/lib/server/services/client.ts
+++ b/src/lib/server/services/client.ts
@@ -34,8 +34,14 @@ const createUserClientChallenge = async (
   encPubKey: string,
 ) => {
   const { answer, challenge } = await generateChallenge(32, encPubKey);
-  await registerUserClientChallenge(userId, clientId, answer.toString("base64"), ip, expiresAt());
-  return challenge.toString("base64");
+  const { id } = await registerUserClientChallenge(
+    userId,
+    clientId,
+    answer.toString("base64"),
+    ip,
+    expiresAt(),
+  );
+  return { id, challenge: challenge.toString("base64") };
 };
 
 export const registerUserClient = async (
@@ -48,7 +54,7 @@ export const registerUserClient = async (
   if (client) {
     try {
       await createUserClient(userId, client.id);
-      return { challenge: await createUserClientChallenge(ip, userId, client.id, encPubKey) };
+      return await createUserClientChallenge(ip, userId, client.id, encPubKey);
     } catch (e) {
       if (e instanceof IntegrityError && e.message === "User client already exists") {
         error(409, "Client already registered");
@@ -64,7 +70,7 @@ export const registerUserClient = async (
 
     try {
       const { id: clientId } = await createClient(encPubKey, sigPubKey, userId);
-      return { challenge: await createUserClientChallenge(ip, userId, clientId, encPubKey) };
+      return await createUserClientChallenge(ip, userId, clientId, encPubKey);
     } catch (e) {
       if (e instanceof IntegrityError && e.message === "Public key(s) already registered") {
         error(409, "Public key(s) already used");
@@ -77,10 +83,10 @@ export const registerUserClient = async (
 export const verifyUserClient = async (
   userId: number,
   ip: string,
-  answer: string,
+  challengeId: number,
   answerSig: string,
 ) => {
-  const challenge = await consumeUserClientChallenge(userId, answer, ip);
+  const challenge = await consumeUserClientChallenge(challengeId, userId, ip);
   if (!challenge) {
     error(403, "Invalid challenge answer");
   }
@@ -88,7 +94,9 @@ export const verifyUserClient = async (
   const client = await getClient(challenge.clientId);
   if (!client) {
     error(500, "Invalid challenge answer");
-  } else if (!verifySignature(Buffer.from(answer, "base64"), answerSig, client.sigPubKey)) {
+  } else if (
+    !verifySignature(Buffer.from(challenge.answer, "base64"), answerSig, client.sigPubKey)
+  ) {
     error(403, "Invalid challenge answer signature");
   }
 
diff --git a/src/lib/services/auth.ts b/src/lib/services/auth.ts
index 498c794..df49e30 100644
--- a/src/lib/services/auth.ts
+++ b/src/lib/services/auth.ts
@@ -18,12 +18,12 @@ export const requestSessionUpgrade = async (
   });
   if (!res.ok) return false;
 
-  const { challenge }: SessionUpgradeResponse = await res.json();
+  const { id, challenge }: SessionUpgradeResponse = await res.json();
   const answer = await decryptChallenge(challenge, decryptKey);
   const answerSig = await signMessageRSA(answer, signKey);
 
   res = await callPostApi<SessionUpgradeVerifyRequest>("/api/auth/upgradeSession/verify", {
-    answer: encodeToBase64(answer),
+    id,
     answerSig: encodeToBase64(answerSig),
   });
   return res.ok;
diff --git a/src/lib/services/key.ts b/src/lib/services/key.ts
index fb368dd..a7e1c08 100644
--- a/src/lib/services/key.ts
+++ b/src/lib/services/key.ts
@@ -27,12 +27,12 @@ export const requestClientRegistration = async (
   });
   if (!res.ok) return false;
 
-  const { challenge }: ClientRegisterResponse = await res.json();
+  const { id, challenge }: ClientRegisterResponse = await res.json();
   const answer = await decryptChallenge(challenge, decryptKey);
   const answerSig = await signMessageRSA(answer, signKey);
 
   res = await callPostApi<ClientRegisterVerifyRequest>("/api/client/register/verify", {
-    answer: encodeToBase64(answer),
+    id,
     answerSig: encodeToBase64(answerSig),
   });
   return res.ok;
diff --git a/src/routes/api/auth/upgradeSession/+server.ts b/src/routes/api/auth/upgradeSession/+server.ts
index 760f4c0..fa0b6cf 100644
--- a/src/routes/api/auth/upgradeSession/+server.ts
+++ b/src/routes/api/auth/upgradeSession/+server.ts
@@ -15,12 +15,12 @@ export const POST: RequestHandler = async ({ locals, request }) => {
   if (!zodRes.success) error(400, "Invalid request body");
   const { encPubKey, sigPubKey } = zodRes.data;
 
-  const { challenge } = await createSessionUpgradeChallenge(
+  const { id, challenge } = await createSessionUpgradeChallenge(
     sessionId,
     userId,
     locals.ip,
     encPubKey,
     sigPubKey,
   );
-  return json(sessionUpgradeResponse.parse({ challenge } satisfies SessionUpgradeResponse));
+  return json(sessionUpgradeResponse.parse({ id, challenge } satisfies SessionUpgradeResponse));
 };
diff --git a/src/routes/api/auth/upgradeSession/verify/+server.ts b/src/routes/api/auth/upgradeSession/verify/+server.ts
index 82cb315..2fe4e36 100644
--- a/src/routes/api/auth/upgradeSession/verify/+server.ts
+++ b/src/routes/api/auth/upgradeSession/verify/+server.ts
@@ -9,8 +9,8 @@ export const POST: RequestHandler = async ({ locals, request }) => {
 
   const zodRes = sessionUpgradeVerifyRequest.safeParse(await request.json());
   if (!zodRes.success) error(400, "Invalid request body");
-  const { answer, answerSig } = zodRes.data;
+  const { id, answerSig } = zodRes.data;
 
-  await verifySessionUpgradeChallenge(sessionId, locals.ip, answer, answerSig);
+  await verifySessionUpgradeChallenge(sessionId, locals.ip, id, answerSig);
   return text("Session upgraded", { headers: { "Content-Type": "text/plain" } });
 };
diff --git a/src/routes/api/client/register/+server.ts b/src/routes/api/client/register/+server.ts
index d6aa4ce..5ac2a53 100644
--- a/src/routes/api/client/register/+server.ts
+++ b/src/routes/api/client/register/+server.ts
@@ -15,6 +15,6 @@ export const POST: RequestHandler = async ({ locals, request }) => {
   if (!zodRes.success) error(400, "Invalid request body");
   const { encPubKey, sigPubKey } = zodRes.data;
 
-  const { challenge } = await registerUserClient(userId, locals.ip, encPubKey, sigPubKey);
-  return json(clientRegisterResponse.parse({ challenge } satisfies ClientRegisterResponse));
+  const { id, challenge } = await registerUserClient(userId, locals.ip, encPubKey, sigPubKey);
+  return json(clientRegisterResponse.parse({ id, challenge } satisfies ClientRegisterResponse));
 };
diff --git a/src/routes/api/client/register/verify/+server.ts b/src/routes/api/client/register/verify/+server.ts
index 32d5214..5ac9396 100644
--- a/src/routes/api/client/register/verify/+server.ts
+++ b/src/routes/api/client/register/verify/+server.ts
@@ -9,8 +9,8 @@ export const POST: RequestHandler = async ({ locals, request }) => {
 
   const zodRes = clientRegisterVerifyRequest.safeParse(await request.json());
   if (!zodRes.success) error(400, "Invalid request body");
-  const { answer, answerSig } = zodRes.data;
+  const { id, answerSig } = zodRes.data;
 
-  await verifyUserClient(userId, locals.ip, answer, answerSig);
+  await verifyUserClient(userId, locals.ip, id, answerSig);
   return text("Client verified", { headers: { "Content-Type": "text/plain" } });
 };