diff --git a/server/domain/user/service/srp/calcSrpA.ts b/server/domain/user/service/srp/calcSrpA.ts
new file mode 100644
index 0000000..152627c
--- /dev/null
+++ b/server/domain/user/service/srp/calcSrpA.ts
@@ -0,0 +1,15 @@
+import { Buffer } from 'buffer';
+import crypto from 'crypto';
+import { N, g } from 'domain/user/service/srp/constants';
+import { fromBuffer, toBuffer } from 'domain/user/service/srp/util';
+import { BigInteger } from 'jsbn';
+
+export const calculateSrpA = (): { a: Buffer; A: Buffer } => {
+  let a = Buffer.from([0]);
+  let AInt = BigInteger.ZERO;
+  while (AInt === BigInteger.ZERO) {
+    a = crypto.randomBytes(32);
+    AInt = g.modPow(fromBuffer(a), N);
+  }
+  return { a, A: toBuffer(AInt) };
+};
diff --git a/server/tests/api/changePassword.test.ts b/server/tests/api/changePassword.test.ts
index b0e6a29..87d96ec 100644
--- a/server/tests/api/changePassword.test.ts
+++ b/server/tests/api/changePassword.test.ts
@@ -1,8 +1,7 @@
 import assert from 'assert';
-import crypto from 'crypto';
 import { calcClientSignature } from 'domain/user/service/srp/calcClientSignature';
-import { N, g } from 'domain/user/service/srp/constants';
-import { fromBuffer, toBuffer } from 'domain/user/service/srp/util';
+import { calculateSrpA } from 'domain/user/service/srp/calcSrpA';
+import { fromBuffer } from 'domain/user/service/srp/util';
 import { DEFAULT_USER_POOL_CLIENT_ID } from 'service/envValues';
 import { test } from 'vitest';
 import {
@@ -15,8 +14,7 @@ import {
 
 test('changePassword', async () => {
   await createUserClient();
-  const a = crypto.randomBytes(32);
-  const A = toBuffer(g.modPow(fromBuffer(a), N));
+  const { a, A } = calculateSrpA();
   const res1 = await noCookieClient.$post({
     headers: { 'x-amz-target': 'AWSCognitoIdentityProviderService.InitiateAuth' },
     body: {
diff --git a/server/tests/api/signIn.test.ts b/server/tests/api/signIn.test.ts
index 63f362c..ea5fbee 100644
--- a/server/tests/api/signIn.test.ts
+++ b/server/tests/api/signIn.test.ts
@@ -1,8 +1,7 @@
 import assert from 'assert';
-import crypto from 'crypto';
 import { calcClientSignature } from 'domain/user/service/srp/calcClientSignature';
-import { N, g } from 'domain/user/service/srp/constants';
-import { fromBuffer, toBuffer } from 'domain/user/service/srp/util';
+import { calculateSrpA } from 'domain/user/service/srp/calcSrpA';
+import { fromBuffer } from 'domain/user/service/srp/util';
 import { DEFAULT_USER_POOL_CLIENT_ID } from 'service/envValues';
 import { expect, test } from 'vitest';
 import {
@@ -16,8 +15,7 @@ import {
 test('signIn', async () => {
   await createUserClient();
 
-  const a = crypto.randomBytes(32);
-  const A = toBuffer(g.modPow(fromBuffer(a), N));
+  const { a, A } = calculateSrpA();
   const res1 = await noCookieClient.$post({
     headers: { 'x-amz-target': 'AWSCognitoIdentityProviderService.InitiateAuth' },
     body: {