diff --git a/apps/web/lib/jwt.test.ts b/apps/web/lib/jwt.test.ts
index de2a4b5a49..28cca14686 100644
--- a/apps/web/lib/jwt.test.ts
+++ b/apps/web/lib/jwt.test.ts
@@ -1,6 +1,7 @@
-import { env } from "@/lib/env";
+import jwt from "jsonwebtoken";
 import { beforeEach, describe, expect, test, vi } from "vitest";
 import { prisma } from "@formbricks/database";
+import * as crypto from "@/lib/crypto";
 import {
   createEmailChangeToken,
   createEmailToken,
@@ -14,12 +15,69 @@ import {
   verifyTokenForLinkSurvey,
 } from "./jwt";
 
+const TEST_ENCRYPTION_KEY = "0".repeat(32); // 32-byte key for AES-256-GCM
+const TEST_NEXTAUTH_SECRET = "test-nextauth-secret";
+const DIFFERENT_SECRET = "different-secret";
+
+// Error message constants
+const NEXTAUTH_SECRET_ERROR = "NEXTAUTH_SECRET is not set";
+const ENCRYPTION_KEY_ERROR = "ENCRYPTION_KEY is not set";
+
+// Helper function to test error cases for missing secrets/keys
+const testMissingSecretsError = async (
+  testFn: (...args: any[]) => any,
+  args: any[],
+  options: {
+    testNextAuthSecret?: boolean;
+    testEncryptionKey?: boolean;
+    isAsync?: boolean;
+  } = {}
+) => {
+  const { testNextAuthSecret = true, testEncryptionKey = true, isAsync = false } = options;
+
+  if (testNextAuthSecret) {
+    const constants = await import("@/lib/constants");
+    const originalSecret = (constants as any).NEXTAUTH_SECRET;
+    (constants as any).NEXTAUTH_SECRET = undefined;
+
+    if (isAsync) {
+      await expect(testFn(...args)).rejects.toThrow(NEXTAUTH_SECRET_ERROR);
+    } else {
+      expect(() => testFn(...args)).toThrow(NEXTAUTH_SECRET_ERROR);
+    }
+
+    // Restore
+    (constants as any).NEXTAUTH_SECRET = originalSecret;
+  }
+
+  if (testEncryptionKey) {
+    const constants = await import("@/lib/constants");
+    const originalKey = (constants as any).ENCRYPTION_KEY;
+    (constants as any).ENCRYPTION_KEY = undefined;
+
+    if (isAsync) {
+      await expect(testFn(...args)).rejects.toThrow(ENCRYPTION_KEY_ERROR);
+    } else {
+      expect(() => testFn(...args)).toThrow(ENCRYPTION_KEY_ERROR);
+    }
+
+    // Restore
+    (constants as any).ENCRYPTION_KEY = originalKey;
+  }
+};
+
 // Mock environment variables
 vi.mock("@/lib/env", () => ({
   env: {
-    ENCRYPTION_KEY: "0".repeat(32), // 32-byte key for AES-256-GCM
+    ENCRYPTION_KEY: "0".repeat(32),
     NEXTAUTH_SECRET: "test-nextauth-secret",
-  } as typeof env,
+  },
+}));
+
+// Mock constants
+vi.mock("@/lib/constants", () => ({
+  NEXTAUTH_SECRET: "test-nextauth-secret",
+  ENCRYPTION_KEY: "0".repeat(32),
 }));
 
 // Mock prisma
@@ -31,22 +89,65 @@ vi.mock("@formbricks/database", () => ({
   },
 }));
 
-describe("JWT Functions", () => {
+// Mock logger
+vi.mock("@formbricks/logger", () => ({
+  logger: {
+    error: vi.fn(),
+    warn: vi.fn(),
+    info: vi.fn(),
+  },
+}));
+
+describe("JWT Functions - Comprehensive Security Tests", () => {
   const mockUser = {
     id: "test-user-id",
     email: "test@example.com",
   };
 
+  let mockSymmetricEncrypt: any;
+  let mockSymmetricDecrypt: any;
+
   beforeEach(() => {
     vi.clearAllMocks();
+
+    // Setup default crypto mocks
+    mockSymmetricEncrypt = vi
+      .spyOn(crypto, "symmetricEncrypt")
+      .mockImplementation((text: string) => `encrypted_${text}`);
+
+    mockSymmetricDecrypt = vi
+      .spyOn(crypto, "symmetricDecrypt")
+      .mockImplementation((encryptedText: string) => encryptedText.replace("encrypted_", ""));
+
     (prisma.user.findUnique as any).mockResolvedValue(mockUser);
   });
 
   describe("createToken", () => {
-    test("should create a valid token", () => {
-      const token = createToken(mockUser.id, mockUser.email);
+    test("should create a valid token with encrypted user ID", () => {
+      const token = createToken(mockUser.id);
       expect(token).toBeDefined();
       expect(typeof token).toBe("string");
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.id, TEST_ENCRYPTION_KEY);
+    });
+
+    test("should accept custom options", () => {
+      const customOptions = { expiresIn: "1h" };
+      const token = createToken(mockUser.id, customOptions);
+      expect(token).toBeDefined();
+
+      // Verify the token contains the expected expiration
+      const decoded = jwt.decode(token) as any;
+      expect(decoded.exp).toBeDefined();
+      expect(decoded.iat).toBeDefined();
+      // Should expire in approximately 1 hour (3600 seconds)
+      expect(decoded.exp - decoded.iat).toBe(3600);
+    });
+
+    test("should throw error if NEXTAUTH_SECRET is not set", async () => {
+      await testMissingSecretsError(createToken, [mockUser.id], {
+        testNextAuthSecret: true,
+        testEncryptionKey: false,
+      });
     });
   });
 
@@ -56,6 +157,18 @@ describe("JWT Functions", () => {
       const token = createTokenForLinkSurvey(surveyId, mockUser.email);
       expect(token).toBeDefined();
       expect(typeof token).toBe("string");
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.email, TEST_ENCRYPTION_KEY);
+    });
+
+    test("should include surveyId in payload", () => {
+      const surveyId = "test-survey-id";
+      const token = createTokenForLinkSurvey(surveyId, mockUser.email);
+      const decoded = jwt.decode(token) as any;
+      expect(decoded.surveyId).toBe(surveyId);
+    });
+
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(createTokenForLinkSurvey, ["survey-id", mockUser.email]);
     });
   });
 
@@ -64,24 +177,30 @@ describe("JWT Functions", () => {
       const token = createEmailToken(mockUser.email);
       expect(token).toBeDefined();
       expect(typeof token).toBe("string");
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.email, TEST_ENCRYPTION_KEY);
     });
 
-    test("should throw error if NEXTAUTH_SECRET is not set", () => {
-      const originalSecret = env.NEXTAUTH_SECRET;
-      try {
-        (env as any).NEXTAUTH_SECRET = undefined;
-        expect(() => createEmailToken(mockUser.email)).toThrow("NEXTAUTH_SECRET is not set");
-      } finally {
-        (env as any).NEXTAUTH_SECRET = originalSecret;
-      }
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(createEmailToken, [mockUser.email]);
     });
   });
 
-  describe("getEmailFromEmailToken", () => {
-    test("should extract email from valid token", () => {
-      const token = createEmailToken(mockUser.email);
-      const extractedEmail = getEmailFromEmailToken(token);
-      expect(extractedEmail).toBe(mockUser.email);
+  describe("createEmailChangeToken", () => {
+    test("should create a valid email change token with 1 day expiration", () => {
+      const token = createEmailChangeToken(mockUser.id, mockUser.email);
+      expect(token).toBeDefined();
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.id, TEST_ENCRYPTION_KEY);
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.email, TEST_ENCRYPTION_KEY);
+
+      const decoded = jwt.decode(token) as any;
+      expect(decoded.exp).toBeDefined();
+      expect(decoded.iat).toBeDefined();
+      // Should expire in approximately 1 day (86400 seconds)
+      expect(decoded.exp - decoded.iat).toBe(86400);
+    });
+
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(createEmailChangeToken, [mockUser.id, mockUser.email]);
     });
   });
 
@@ -91,6 +210,50 @@ describe("JWT Functions", () => {
       const token = createInviteToken(inviteId, mockUser.email);
       expect(token).toBeDefined();
       expect(typeof token).toBe("string");
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(inviteId, TEST_ENCRYPTION_KEY);
+      expect(mockSymmetricEncrypt).toHaveBeenCalledWith(mockUser.email, TEST_ENCRYPTION_KEY);
+    });
+
+    test("should accept custom options", () => {
+      const inviteId = "test-invite-id";
+      const customOptions = { expiresIn: "24h" };
+      const token = createInviteToken(inviteId, mockUser.email, customOptions);
+      expect(token).toBeDefined();
+
+      const decoded = jwt.decode(token) as any;
+      expect(decoded.exp).toBeDefined();
+      expect(decoded.iat).toBeDefined();
+      // Should expire in approximately 24 hours (86400 seconds)
+      expect(decoded.exp - decoded.iat).toBe(86400);
+    });
+
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(createInviteToken, ["invite-id", mockUser.email]);
+    });
+  });
+
+  describe("getEmailFromEmailToken", () => {
+    test("should extract email from valid token", () => {
+      const token = createEmailToken(mockUser.email);
+      const extractedEmail = getEmailFromEmailToken(token);
+      expect(extractedEmail).toBe(mockUser.email);
+      expect(mockSymmetricDecrypt).toHaveBeenCalledWith(`encrypted_${mockUser.email}`, TEST_ENCRYPTION_KEY);
+    });
+
+    test("should fall back to original email if decryption fails", () => {
+      mockSymmetricDecrypt.mockImplementationOnce(() => {
+        throw new Error("Decryption failed");
+      });
+
+      // Create token manually with unencrypted email for legacy compatibility
+      const legacyToken = jwt.sign({ email: mockUser.email }, TEST_NEXTAUTH_SECRET);
+      const extractedEmail = getEmailFromEmailToken(legacyToken);
+      expect(extractedEmail).toBe(mockUser.email);
+    });
+
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      const token = jwt.sign({ email: "test@example.com" }, TEST_NEXTAUTH_SECRET);
+      await testMissingSecretsError(getEmailFromEmailToken, [token]);
     });
   });
 
@@ -106,23 +269,194 @@ describe("JWT Functions", () => {
       const result = verifyTokenForLinkSurvey("invalid-token", "test-survey-id");
       expect(result).toBeNull();
     });
+
+    test("should return null if NEXTAUTH_SECRET is not set", async () => {
+      const constants = await import("@/lib/constants");
+      const originalSecret = (constants as any).NEXTAUTH_SECRET;
+      (constants as any).NEXTAUTH_SECRET = undefined;
+
+      const result = verifyTokenForLinkSurvey("any-token", "test-survey-id");
+      expect(result).toBeNull();
+
+      // Restore
+      (constants as any).NEXTAUTH_SECRET = originalSecret;
+    });
+
+    test("should return null if surveyId doesn't match", () => {
+      const surveyId = "test-survey-id";
+      const differentSurveyId = "different-survey-id";
+      const token = createTokenForLinkSurvey(surveyId, mockUser.email);
+      const result = verifyTokenForLinkSurvey(token, differentSurveyId);
+      expect(result).toBeNull();
+    });
+
+    test("should return null if email is missing from payload", () => {
+      const tokenWithoutEmail = jwt.sign({ surveyId: "test-survey-id" }, TEST_NEXTAUTH_SECRET);
+      const result = verifyTokenForLinkSurvey(tokenWithoutEmail, "test-survey-id");
+      expect(result).toBeNull();
+    });
+
+    test("should fall back to original email if decryption fails", () => {
+      mockSymmetricDecrypt.mockImplementationOnce(() => {
+        throw new Error("Decryption failed");
+      });
+
+      // Create legacy token with unencrypted email
+      const legacyToken = jwt.sign(
+        {
+          email: mockUser.email,
+          surveyId: "test-survey-id",
+        },
+        TEST_NEXTAUTH_SECRET
+      );
+
+      const result = verifyTokenForLinkSurvey(legacyToken, "test-survey-id");
+      expect(result).toBe(mockUser.email);
+    });
+
+    test("should fall back to original email if ENCRYPTION_KEY is not set", async () => {
+      const constants = await import("@/lib/constants");
+      const originalKey = (constants as any).ENCRYPTION_KEY;
+      (constants as any).ENCRYPTION_KEY = undefined;
+
+      // Create a token with unencrypted email (as it would be if ENCRYPTION_KEY was not set during creation)
+      const token = jwt.sign(
+        {
+          email: mockUser.email,
+          surveyId: "survey-id",
+        },
+        TEST_NEXTAUTH_SECRET
+      );
+
+      const result = verifyTokenForLinkSurvey(token, "survey-id");
+      expect(result).toBe(mockUser.email);
+
+      // Restore
+      (constants as any).ENCRYPTION_KEY = originalKey;
+    });
+
+    test("should verify legacy survey tokens with surveyId-based secret", async () => {
+      const surveyId = "test-survey-id";
+
+      // Create legacy token with old format (NEXTAUTH_SECRET + surveyId)
+      const legacyToken = jwt.sign({ email: `encrypted_${mockUser.email}` }, TEST_NEXTAUTH_SECRET + surveyId);
+
+      const result = verifyTokenForLinkSurvey(legacyToken, surveyId);
+      expect(result).toBe(mockUser.email);
+    });
+
+    test("should reject survey tokens that fail both new and legacy verification", async () => {
+      const surveyId = "test-survey-id";
+      const invalidToken = jwt.sign({ email: "encrypted_test@example.com" }, "wrong-secret");
+
+      const result = verifyTokenForLinkSurvey(invalidToken, surveyId);
+      expect(result).toBeNull();
+
+      // Verify error logging
+      const { logger } = await import("@formbricks/logger");
+      expect(logger.error).toHaveBeenCalledWith(expect.any(Error), "Survey link token verification failed");
+    });
+
+    test("should reject legacy survey tokens for wrong survey", () => {
+      const correctSurveyId = "correct-survey-id";
+      const wrongSurveyId = "wrong-survey-id";
+
+      // Create legacy token for one survey
+      const legacyToken = jwt.sign(
+        { email: `encrypted_${mockUser.email}` },
+        TEST_NEXTAUTH_SECRET + correctSurveyId
+      );
+
+      // Try to verify with different survey ID
+      const result = verifyTokenForLinkSurvey(legacyToken, wrongSurveyId);
+      expect(result).toBeNull();
+    });
   });
 
   describe("verifyToken", () => {
     test("should verify valid token", async () => {
-      const token = createToken(mockUser.id, mockUser.email);
+      const token = createToken(mockUser.id);
       const verified = await verifyToken(token);
       expect(verified).toEqual({
-        id: mockUser.id,
+        id: mockUser.id, // Returns the decrypted user ID
         email: mockUser.email,
       });
     });
 
     test("should throw error if user not found", async () => {
       (prisma.user.findUnique as any).mockResolvedValue(null);
-      const token = createToken(mockUser.id, mockUser.email);
+      const token = createToken(mockUser.id);
       await expect(verifyToken(token)).rejects.toThrow("User not found");
     });
+
+    test("should throw error if NEXTAUTH_SECRET is not set", async () => {
+      await testMissingSecretsError(verifyToken, ["any-token"], {
+        testNextAuthSecret: true,
+        testEncryptionKey: false,
+        isAsync: true,
+      });
+    });
+
+    test("should throw error for invalid token signature", async () => {
+      const invalidToken = jwt.sign({ id: "test-id" }, DIFFERENT_SECRET);
+      await expect(verifyToken(invalidToken)).rejects.toThrow("Invalid token");
+    });
+
+    test("should throw error if token payload is missing id", async () => {
+      const tokenWithoutId = jwt.sign({ email: mockUser.email }, TEST_NEXTAUTH_SECRET);
+      await expect(verifyToken(tokenWithoutId)).rejects.toThrow("Invalid token");
+    });
+
+    test("should return raw id from payload", async () => {
+      // Create token with unencrypted id
+      const token = jwt.sign({ id: mockUser.id }, TEST_NEXTAUTH_SECRET);
+      const verified = await verifyToken(token);
+      expect(verified).toEqual({
+        id: mockUser.id, // Returns the raw ID from payload
+        email: mockUser.email,
+      });
+    });
+
+    test("should verify legacy tokens with email-based secret", async () => {
+      // Create legacy token with old format (NEXTAUTH_SECRET + userEmail)
+      const legacyToken = jwt.sign({ id: `encrypted_${mockUser.id}` }, TEST_NEXTAUTH_SECRET + mockUser.email);
+
+      const verified = await verifyToken(legacyToken);
+      expect(verified).toEqual({
+        id: mockUser.id, // Returns the decrypted user ID
+        email: mockUser.email,
+      });
+    });
+
+    test("should prioritize new tokens over legacy tokens", async () => {
+      // Create both new and legacy tokens for the same user
+      const newToken = createToken(mockUser.id);
+      const legacyToken = jwt.sign({ id: `encrypted_${mockUser.id}` }, TEST_NEXTAUTH_SECRET + mockUser.email);
+
+      // New token should verify without triggering legacy path
+      const verifiedNew = await verifyToken(newToken);
+      expect(verifiedNew.id).toBe(mockUser.id); // Returns decrypted user ID
+
+      // Legacy token should trigger legacy path
+      const verifiedLegacy = await verifyToken(legacyToken);
+      expect(verifiedLegacy.id).toBe(mockUser.id); // Returns decrypted user ID
+    });
+
+    test("should reject tokens that fail both new and legacy verification", async () => {
+      const invalidToken = jwt.sign({ id: "encrypted_test-id" }, "wrong-secret");
+      await expect(verifyToken(invalidToken)).rejects.toThrow("Invalid token");
+
+      // Verify both methods were attempted
+      const { logger } = await import("@formbricks/logger");
+      expect(logger.error).toHaveBeenCalledWith(
+        expect.any(Error),
+        "Token verification failed with new method"
+      );
+      expect(logger.error).toHaveBeenCalledWith(
+        expect.any(Error),
+        "Token verification failed with legacy method"
+      );
+    });
   });
 
   describe("verifyInviteToken", () => {
@@ -139,6 +473,53 @@ describe("JWT Functions", () => {
     test("should throw error for invalid token", () => {
       expect(() => verifyInviteToken("invalid-token")).toThrow("Invalid or expired invite token");
     });
+
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(verifyInviteToken, ["any-token"]);
+    });
+
+    test("should throw error if inviteId is missing", () => {
+      const tokenWithoutInviteId = jwt.sign({ email: mockUser.email }, TEST_NEXTAUTH_SECRET);
+      expect(() => verifyInviteToken(tokenWithoutInviteId)).toThrow("Invalid or expired invite token");
+    });
+
+    test("should throw error if email is missing", () => {
+      const tokenWithoutEmail = jwt.sign({ inviteId: "test-invite-id" }, TEST_NEXTAUTH_SECRET);
+      expect(() => verifyInviteToken(tokenWithoutEmail)).toThrow("Invalid or expired invite token");
+    });
+
+    test("should fall back to original values if decryption fails", () => {
+      mockSymmetricDecrypt.mockImplementation(() => {
+        throw new Error("Decryption failed");
+      });
+
+      const inviteId = "test-invite-id";
+      const legacyToken = jwt.sign(
+        {
+          inviteId,
+          email: mockUser.email,
+        },
+        TEST_NEXTAUTH_SECRET
+      );
+
+      const verified = verifyInviteToken(legacyToken);
+      expect(verified).toEqual({
+        inviteId,
+        email: mockUser.email,
+      });
+    });
+
+    test("should throw error for token with wrong signature", () => {
+      const invalidToken = jwt.sign(
+        {
+          inviteId: "test-invite-id",
+          email: mockUser.email,
+        },
+        DIFFERENT_SECRET
+      );
+
+      expect(() => verifyInviteToken(invalidToken)).toThrow("Invalid or expired invite token");
+    });
   });
 
   describe("verifyEmailChangeToken", () => {
@@ -150,22 +531,478 @@ describe("JWT Functions", () => {
       expect(result).toEqual({ id: userId, email });
     });
 
+    test("should throw error if NEXTAUTH_SECRET or ENCRYPTION_KEY is not set", async () => {
+      await testMissingSecretsError(verifyEmailChangeToken, ["any-token"], { isAsync: true });
+    });
+
     test("should throw error if token is invalid or missing fields", async () => {
-      // Create a token with missing fields
-      const jwt = await import("jsonwebtoken");
-      const token = jwt.sign({ foo: "bar" }, env.NEXTAUTH_SECRET as string);
+      const token = jwt.sign({ foo: "bar" }, TEST_NEXTAUTH_SECRET);
+      await expect(verifyEmailChangeToken(token)).rejects.toThrow(
+        "Token is invalid or missing required fields"
+      );
+    });
+
+    test("should throw error if id is missing", async () => {
+      const token = jwt.sign({ email: "test@example.com" }, TEST_NEXTAUTH_SECRET);
+      await expect(verifyEmailChangeToken(token)).rejects.toThrow(
+        "Token is invalid or missing required fields"
+      );
+    });
+
+    test("should throw error if email is missing", async () => {
+      const token = jwt.sign({ id: "test-id" }, TEST_NEXTAUTH_SECRET);
       await expect(verifyEmailChangeToken(token)).rejects.toThrow(
         "Token is invalid or missing required fields"
       );
     });
 
     test("should return original id/email if decryption fails", async () => {
-      // Create a token with non-encrypted id/email
-      const jwt = await import("jsonwebtoken");
+      mockSymmetricDecrypt.mockImplementation(() => {
+        throw new Error("Decryption failed");
+      });
+
       const payload = { id: "plain-id", email: "plain@example.com" };
-      const token = jwt.sign(payload, env.NEXTAUTH_SECRET as string);
+      const token = jwt.sign(payload, TEST_NEXTAUTH_SECRET);
       const result = await verifyEmailChangeToken(token);
       expect(result).toEqual(payload);
     });
+
+    test("should throw error for token with wrong signature", async () => {
+      const invalidToken = jwt.sign(
+        {
+          id: "test-id",
+          email: "test@example.com",
+        },
+        DIFFERENT_SECRET
+      );
+
+      await expect(verifyEmailChangeToken(invalidToken)).rejects.toThrow();
+    });
+  });
+
+  // SECURITY SCENARIO TESTS
+  describe("Security Scenarios", () => {
+    describe("Algorithm Confusion Attack Prevention", () => {
+      test("should reject 'none' algorithm tokens in verifyToken", async () => {
+        // Create malicious token with "none" algorithm
+        const maliciousToken =
+          Buffer.from(
+            JSON.stringify({
+              alg: "none",
+              typ: "JWT",
+            })
+          ).toString("base64url") +
+          "." +
+          Buffer.from(
+            JSON.stringify({
+              id: "encrypted_malicious-id",
+            })
+          ).toString("base64url") +
+          ".";
+
+        await expect(verifyToken(maliciousToken)).rejects.toThrow("Invalid token");
+      });
+
+      test("should reject 'none' algorithm tokens in verifyTokenForLinkSurvey", () => {
+        const maliciousToken =
+          Buffer.from(
+            JSON.stringify({
+              alg: "none",
+              typ: "JWT",
+            })
+          ).toString("base64url") +
+          "." +
+          Buffer.from(
+            JSON.stringify({
+              email: "encrypted_attacker@evil.com",
+              surveyId: "test-survey-id",
+            })
+          ).toString("base64url") +
+          ".";
+
+        const result = verifyTokenForLinkSurvey(maliciousToken, "test-survey-id");
+        expect(result).toBeNull();
+      });
+
+      test("should reject 'none' algorithm tokens in verifyInviteToken", () => {
+        const maliciousToken =
+          Buffer.from(
+            JSON.stringify({
+              alg: "none",
+              typ: "JWT",
+            })
+          ).toString("base64url") +
+          "." +
+          Buffer.from(
+            JSON.stringify({
+              inviteId: "encrypted_malicious-invite",
+              email: "encrypted_attacker@evil.com",
+            })
+          ).toString("base64url") +
+          ".";
+
+        expect(() => verifyInviteToken(maliciousToken)).toThrow("Invalid or expired invite token");
+      });
+
+      test("should reject 'none' algorithm tokens in verifyEmailChangeToken", async () => {
+        const maliciousToken =
+          Buffer.from(
+            JSON.stringify({
+              alg: "none",
+              typ: "JWT",
+            })
+          ).toString("base64url") +
+          "." +
+          Buffer.from(
+            JSON.stringify({
+              id: "encrypted_malicious-id",
+              email: "encrypted_attacker@evil.com",
+            })
+          ).toString("base64url") +
+          ".";
+
+        await expect(verifyEmailChangeToken(maliciousToken)).rejects.toThrow();
+      });
+
+      test("should reject RS256 algorithm tokens (HS256/RS256 confusion)", async () => {
+        // Create malicious token with RS256 algorithm header but HS256 signature
+        const maliciousHeader = Buffer.from(
+          JSON.stringify({
+            alg: "RS256",
+            typ: "JWT",
+          })
+        ).toString("base64url");
+
+        const maliciousPayload = Buffer.from(
+          JSON.stringify({
+            id: "encrypted_malicious-id",
+          })
+        ).toString("base64url");
+
+        // Create signature using HMAC (as if it were HS256)
+        const crypto = require("crypto");
+        const signature = crypto
+          .createHmac("sha256", TEST_NEXTAUTH_SECRET)
+          .update(`${maliciousHeader}.${maliciousPayload}`)
+          .digest("base64url");
+
+        const maliciousToken = `${maliciousHeader}.${maliciousPayload}.${signature}`;
+
+        await expect(verifyToken(maliciousToken)).rejects.toThrow("Invalid token");
+      });
+
+      test("should only accept HS256 algorithm", async () => {
+        // Test that other valid algorithms are rejected
+        const otherAlgorithms = ["HS384", "HS512", "RS256", "RS384", "RS512", "ES256", "ES384", "ES512"];
+
+        for (const alg of otherAlgorithms) {
+          const maliciousHeader = Buffer.from(
+            JSON.stringify({
+              alg,
+              typ: "JWT",
+            })
+          ).toString("base64url");
+
+          const maliciousPayload = Buffer.from(
+            JSON.stringify({
+              id: "encrypted_test-id",
+            })
+          ).toString("base64url");
+
+          const maliciousToken = `${maliciousHeader}.${maliciousPayload}.fake-signature`;
+
+          await expect(verifyToken(maliciousToken)).rejects.toThrow("Invalid token");
+        }
+      });
+    });
+
+    describe("Token Tampering", () => {
+      test("should reject tokens with modified payload", async () => {
+        const token = createToken(mockUser.id);
+        const [header, payload, signature] = token.split(".");
+
+        // Modify the payload
+        const decodedPayload = JSON.parse(Buffer.from(payload, "base64url").toString());
+        decodedPayload.id = "malicious-id";
+        const tamperedPayload = Buffer.from(JSON.stringify(decodedPayload)).toString("base64url");
+        const tamperedToken = `${header}.${tamperedPayload}.${signature}`;
+
+        await expect(verifyToken(tamperedToken)).rejects.toThrow("Invalid token");
+      });
+
+      test("should reject tokens with modified signature", async () => {
+        const token = createToken(mockUser.id);
+        const [header, payload] = token.split(".");
+        const tamperedToken = `${header}.${payload}.tamperedsignature`;
+
+        await expect(verifyToken(tamperedToken)).rejects.toThrow("Invalid token");
+      });
+
+      test("should reject malformed tokens", async () => {
+        const malformedTokens = [
+          "not.a.jwt",
+          "only.two.parts",
+          "too.many.parts.here.invalid",
+          "",
+          "invalid-base64",
+        ];
+
+        for (const malformedToken of malformedTokens) {
+          await expect(verifyToken(malformedToken)).rejects.toThrow();
+        }
+      });
+    });
+
+    describe("Cross-Survey Token Reuse", () => {
+      test("should reject survey tokens used for different surveys", () => {
+        const surveyId1 = "survey-1";
+        const surveyId2 = "survey-2";
+
+        const token = createTokenForLinkSurvey(surveyId1, mockUser.email);
+        const result = verifyTokenForLinkSurvey(token, surveyId2);
+
+        expect(result).toBeNull();
+      });
+    });
+
+    describe("Expired Tokens", () => {
+      test("should reject expired tokens", async () => {
+        const expiredToken = jwt.sign(
+          {
+            id: "encrypted_test-id",
+            exp: Math.floor(Date.now() / 1000) - 3600, // Expired 1 hour ago
+          },
+          TEST_NEXTAUTH_SECRET
+        );
+
+        await expect(verifyToken(expiredToken)).rejects.toThrow("Invalid token");
+      });
+
+      test("should reject expired email change tokens", async () => {
+        const expiredToken = jwt.sign(
+          {
+            id: "encrypted_test-id",
+            email: "encrypted_test@example.com",
+            exp: Math.floor(Date.now() / 1000) - 3600, // Expired 1 hour ago
+          },
+          TEST_NEXTAUTH_SECRET
+        );
+
+        await expect(verifyEmailChangeToken(expiredToken)).rejects.toThrow();
+      });
+    });
+
+    describe("Encryption Key Attacks", () => {
+      test("should fail gracefully with wrong encryption key", async () => {
+        mockSymmetricDecrypt.mockImplementation(() => {
+          throw new Error("Authentication tag verification failed");
+        });
+
+        // Mock findUnique to only return user for correct decrypted ID, not ciphertext
+        (prisma.user.findUnique as any).mockImplementation(({ where }: { where: { id: string } }) => {
+          if (where.id === mockUser.id) {
+            return Promise.resolve(mockUser);
+          }
+          return Promise.resolve(null); // Return null for ciphertext IDs
+        });
+
+        const token = createToken(mockUser.id);
+        // Should fail because ciphertext passed as userId won't match any user in DB
+        await expect(verifyToken(token)).rejects.toThrow(/User not found/i);
+      });
+
+      test("should handle encryption key not set gracefully", async () => {
+        const constants = await import("@/lib/constants");
+        const originalKey = (constants as any).ENCRYPTION_KEY;
+        (constants as any).ENCRYPTION_KEY = undefined;
+
+        const token = jwt.sign(
+          {
+            email: "test@example.com",
+            surveyId: "test-survey-id",
+          },
+          TEST_NEXTAUTH_SECRET
+        );
+
+        const result = verifyTokenForLinkSurvey(token, "test-survey-id");
+        expect(result).toBe("test@example.com");
+
+        // Restore
+        (constants as any).ENCRYPTION_KEY = originalKey;
+      });
+    });
+
+    describe("SQL Injection Attempts", () => {
+      test("should safely handle malicious user IDs", async () => {
+        const maliciousIds = [
+          "'; DROP TABLE users; --",
+          "1' OR '1'='1",
+          "admin'/*",
+          "<script>alert('xss')</script>",
+          "../../etc/passwd",
+        ];
+
+        for (const maliciousId of maliciousIds) {
+          mockSymmetricDecrypt.mockReturnValueOnce(maliciousId);
+
+          const token = jwt.sign({ id: "encrypted_malicious" }, TEST_NEXTAUTH_SECRET);
+
+          // The function should look up the user safely
+          await verifyToken(token);
+          expect(prisma.user.findUnique).toHaveBeenCalledWith({
+            where: { id: maliciousId },
+          });
+        }
+      });
+    });
+
+    describe("Token Reuse and Replay Attacks", () => {
+      test("should allow legitimate token reuse within validity period", async () => {
+        const token = createToken(mockUser.id);
+
+        // First use
+        const result1 = await verifyToken(token);
+        expect(result1.id).toBe(mockUser.id); // Returns decrypted user ID
+
+        // Second use (should still work)
+        const result2 = await verifyToken(token);
+        expect(result2.id).toBe(mockUser.id); // Returns decrypted user ID
+      });
+    });
+
+    describe("Legacy Token Compatibility", () => {
+      test("should handle legacy unencrypted tokens gracefully", async () => {
+        // Legacy token with plain text data
+        const legacyToken = jwt.sign({ id: mockUser.id }, TEST_NEXTAUTH_SECRET);
+        const result = await verifyToken(legacyToken);
+
+        expect(result.id).toBe(mockUser.id); // Returns raw ID from payload
+        expect(result.email).toBe(mockUser.email);
+      });
+
+      test("should handle mixed encrypted/unencrypted fields", async () => {
+        mockSymmetricDecrypt
+          .mockImplementationOnce(() => mockUser.id) // id decrypts successfully
+          .mockImplementationOnce(() => {
+            throw new Error("Email not encrypted");
+          }); // email fails
+
+        const token = jwt.sign(
+          {
+            id: "encrypted_test-id",
+            email: "plain-email@example.com",
+          },
+          TEST_NEXTAUTH_SECRET
+        );
+
+        const result = await verifyEmailChangeToken(token);
+        expect(result.id).toBe(mockUser.id);
+        expect(result.email).toBe("plain-email@example.com");
+      });
+
+      test("should verify old format user tokens with email-based secrets", async () => {
+        // Simulate old token format with per-user secret
+        const oldFormatToken = jwt.sign(
+          { id: `encrypted_${mockUser.id}` },
+          TEST_NEXTAUTH_SECRET + mockUser.email
+        );
+
+        const result = await verifyToken(oldFormatToken);
+        expect(result.id).toBe(mockUser.id); // Returns decrypted user ID
+        expect(result.email).toBe(mockUser.email);
+      });
+
+      test("should verify old format survey tokens with survey-based secrets", () => {
+        const surveyId = "legacy-survey-id";
+
+        // Simulate old survey token format
+        const oldFormatSurveyToken = jwt.sign(
+          { email: `encrypted_${mockUser.email}` },
+          TEST_NEXTAUTH_SECRET + surveyId
+        );
+
+        const result = verifyTokenForLinkSurvey(oldFormatSurveyToken, surveyId);
+        expect(result).toBe(mockUser.email);
+      });
+
+      test("should gracefully handle database errors during legacy verification", async () => {
+        // Create token that will fail new method
+        const legacyToken = jwt.sign(
+          { id: `encrypted_${mockUser.id}` },
+          TEST_NEXTAUTH_SECRET + mockUser.email
+        );
+
+        // Make database lookup fail
+        (prisma.user.findUnique as any).mockRejectedValueOnce(new Error("DB connection lost"));
+
+        await expect(verifyToken(legacyToken)).rejects.toThrow("DB connection lost");
+      });
+    });
+
+    describe("Edge Cases and Error Handling", () => {
+      test("should handle database connection errors gracefully", async () => {
+        (prisma.user.findUnique as any).mockRejectedValue(new Error("Database connection failed"));
+
+        const token = createToken(mockUser.id);
+        await expect(verifyToken(token)).rejects.toThrow("Database connection failed");
+      });
+
+      test("should handle crypto module errors", () => {
+        mockSymmetricEncrypt.mockImplementation(() => {
+          throw new Error("Crypto module error");
+        });
+
+        expect(() => createToken(mockUser.id)).toThrow("Crypto module error");
+      });
+
+      test("should validate email format in tokens", () => {
+        const invalidEmails = ["", "not-an-email", "missing@", "@missing-local.com", "spaces in@email.com"];
+
+        invalidEmails.forEach((invalidEmail) => {
+          expect(() => createEmailToken(invalidEmail)).not.toThrow();
+          // Note: JWT functions don't validate email format, they just encrypt/decrypt
+          // Email validation should happen at a higher level
+        });
+      });
+
+      test("should handle extremely long inputs", () => {
+        const longString = "a".repeat(10000);
+
+        expect(() => createToken(longString)).not.toThrow();
+        expect(() => createEmailToken(longString)).not.toThrow();
+      });
+
+      test("should handle special characters in user data", () => {
+        const specialChars = "!@#$%^&*()_+-=[]{}|;:'\",.<>?/~`";
+
+        expect(() => createToken(specialChars)).not.toThrow();
+        expect(() => createEmailToken(specialChars)).not.toThrow();
+      });
+    });
+
+    describe("Performance and Resource Exhaustion", () => {
+      test("should handle rapid token creation without memory leaks", () => {
+        const tokens: string[] = [];
+        for (let i = 0; i < 1000; i++) {
+          tokens.push(createToken(`user-${i}`));
+        }
+
+        expect(tokens.length).toBe(1000);
+        expect(tokens.every((token) => typeof token === "string")).toBe(true);
+      });
+
+      test("should handle rapid token verification", async () => {
+        const token = createToken(mockUser.id);
+
+        const verifications: Promise<any>[] = [];
+        for (let i = 0; i < 100; i++) {
+          verifications.push(verifyToken(token));
+        }
+
+        const results = await Promise.all(verifications);
+        expect(results.length).toBe(100);
+        expect(results.every((result: any) => result.id === mockUser.id)).toBe(true); // Returns decrypted user ID
+      });
+    });
   });
 });
diff --git a/apps/web/lib/jwt.ts b/apps/web/lib/jwt.ts
index 88095db6bc..66e305e2b8 100644
--- a/apps/web/lib/jwt.ts
+++ b/apps/web/lib/jwt.ts
@@ -1,43 +1,64 @@
-import { symmetricDecrypt, symmetricEncrypt } from "@/lib/crypto";
-import { env } from "@/lib/env";
 import jwt, { JwtPayload } from "jsonwebtoken";
 import { prisma } from "@formbricks/database";
 import { logger } from "@formbricks/logger";
+import { ENCRYPTION_KEY, NEXTAUTH_SECRET } from "@/lib/constants";
+import { symmetricDecrypt, symmetricEncrypt } from "@/lib/crypto";
 
-export const createToken = (userId: string, userEmail: string, options = {}): string => {
-  const encryptedUserId = symmetricEncrypt(userId, env.ENCRYPTION_KEY);
-  return jwt.sign({ id: encryptedUserId }, env.NEXTAUTH_SECRET + userEmail, options);
-};
-export const createTokenForLinkSurvey = (surveyId: string, userEmail: string): string => {
-  const encryptedEmail = symmetricEncrypt(userEmail, env.ENCRYPTION_KEY);
-  return jwt.sign({ email: encryptedEmail }, env.NEXTAUTH_SECRET + surveyId);
+// Helper function to decrypt with fallback to plain text
+const decryptWithFallback = (encryptedText: string, key: string): string => {
+  try {
+    return symmetricDecrypt(encryptedText, key);
+  } catch {
+    return encryptedText; // Return as-is if decryption fails (legacy format)
+  }
 };
 
-export const verifyEmailChangeToken = async (token: string): Promise<{ id: string; email: string }> => {
-  if (!env.NEXTAUTH_SECRET) {
+export const createToken = (userId: string, options = {}): string => {
+  if (!NEXTAUTH_SECRET) {
     throw new Error("NEXTAUTH_SECRET is not set");
   }
 
-  const payload = jwt.verify(token, env.NEXTAUTH_SECRET) as { id: string; email: string };
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const encryptedUserId = symmetricEncrypt(userId, ENCRYPTION_KEY);
+  return jwt.sign({ id: encryptedUserId }, NEXTAUTH_SECRET, options);
+};
+export const createTokenForLinkSurvey = (surveyId: string, userEmail: string): string => {
+  if (!NEXTAUTH_SECRET) {
+    throw new Error("NEXTAUTH_SECRET is not set");
+  }
+
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const encryptedEmail = symmetricEncrypt(userEmail, ENCRYPTION_KEY);
+  return jwt.sign({ email: encryptedEmail, surveyId }, NEXTAUTH_SECRET);
+};
+
+export const verifyEmailChangeToken = async (token: string): Promise<{ id: string; email: string }> => {
+  if (!NEXTAUTH_SECRET) {
+    throw new Error("NEXTAUTH_SECRET is not set");
+  }
+
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const payload = jwt.verify(token, NEXTAUTH_SECRET, { algorithms: ["HS256"] }) as {
+    id: string;
+    email: string;
+  };
 
   if (!payload?.id || !payload?.email) {
     throw new Error("Token is invalid or missing required fields");
   }
 
-  let decryptedId: string;
-  let decryptedEmail: string;
-
-  try {
-    decryptedId = symmetricDecrypt(payload.id, env.ENCRYPTION_KEY);
-  } catch {
-    decryptedId = payload.id;
-  }
-
-  try {
-    decryptedEmail = symmetricDecrypt(payload.email, env.ENCRYPTION_KEY);
-  } catch {
-    decryptedEmail = payload.email;
-  }
+  // Decrypt both fields with fallback
+  const decryptedId = decryptWithFallback(payload.id, ENCRYPTION_KEY);
+  const decryptedEmail = decryptWithFallback(payload.email, ENCRYPTION_KEY);
 
   return {
     id: decryptedId,
@@ -46,127 +67,230 @@ export const verifyEmailChangeToken = async (token: string): Promise<{ id: strin
 };
 
 export const createEmailChangeToken = (userId: string, email: string): string => {
-  const encryptedUserId = symmetricEncrypt(userId, env.ENCRYPTION_KEY);
-  const encryptedEmail = symmetricEncrypt(email, env.ENCRYPTION_KEY);
+  if (!NEXTAUTH_SECRET) {
+    throw new Error("NEXTAUTH_SECRET is not set");
+  }
+
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const encryptedUserId = symmetricEncrypt(userId, ENCRYPTION_KEY);
+  const encryptedEmail = symmetricEncrypt(email, ENCRYPTION_KEY);
 
   const payload = {
     id: encryptedUserId,
     email: encryptedEmail,
   };
 
-  return jwt.sign(payload, env.NEXTAUTH_SECRET as string, {
+  return jwt.sign(payload, NEXTAUTH_SECRET, {
     expiresIn: "1d",
   });
 };
+
 export const createEmailToken = (email: string): string => {
-  if (!env.NEXTAUTH_SECRET) {
+  if (!NEXTAUTH_SECRET) {
     throw new Error("NEXTAUTH_SECRET is not set");
   }
 
-  const encryptedEmail = symmetricEncrypt(email, env.ENCRYPTION_KEY);
-  return jwt.sign({ email: encryptedEmail }, env.NEXTAUTH_SECRET);
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const encryptedEmail = symmetricEncrypt(email, ENCRYPTION_KEY);
+  return jwt.sign({ email: encryptedEmail }, NEXTAUTH_SECRET);
 };
 
 export const getEmailFromEmailToken = (token: string): string => {
-  if (!env.NEXTAUTH_SECRET) {
+  if (!NEXTAUTH_SECRET) {
     throw new Error("NEXTAUTH_SECRET is not set");
   }
 
-  const payload = jwt.verify(token, env.NEXTAUTH_SECRET) as JwtPayload;
-  try {
-    // Try to decrypt first (for newer tokens)
-    const decryptedEmail = symmetricDecrypt(payload.email, env.ENCRYPTION_KEY);
-    return decryptedEmail;
-  } catch {
-    // If decryption fails, return the original email (for older tokens)
-    return payload.email;
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
   }
+
+  const payload = jwt.verify(token, NEXTAUTH_SECRET, { algorithms: ["HS256"] }) as JwtPayload & {
+    email: string;
+  };
+  return decryptWithFallback(payload.email, ENCRYPTION_KEY);
 };
 
 export const createInviteToken = (inviteId: string, email: string, options = {}): string => {
-  if (!env.NEXTAUTH_SECRET) {
+  if (!NEXTAUTH_SECRET) {
     throw new Error("NEXTAUTH_SECRET is not set");
   }
-  const encryptedInviteId = symmetricEncrypt(inviteId, env.ENCRYPTION_KEY);
-  const encryptedEmail = symmetricEncrypt(email, env.ENCRYPTION_KEY);
-  return jwt.sign({ inviteId: encryptedInviteId, email: encryptedEmail }, env.NEXTAUTH_SECRET, options);
+
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
+  const encryptedInviteId = symmetricEncrypt(inviteId, ENCRYPTION_KEY);
+  const encryptedEmail = symmetricEncrypt(email, ENCRYPTION_KEY);
+  return jwt.sign({ inviteId: encryptedInviteId, email: encryptedEmail }, NEXTAUTH_SECRET, options);
 };
 
 export const verifyTokenForLinkSurvey = (token: string, surveyId: string): string | null => {
+  if (!NEXTAUTH_SECRET) {
+    return null;
+  }
+
   try {
-    const { email } = jwt.verify(token, env.NEXTAUTH_SECRET + surveyId) as JwtPayload;
+    let payload: JwtPayload & { email: string; surveyId?: string };
+
+    // Try primary method first (consistent secret)
     try {
-      // Try to decrypt first (for newer tokens)
-      if (!env.ENCRYPTION_KEY) {
-        throw new Error("ENCRYPTION_KEY is not set");
+      payload = jwt.verify(token, NEXTAUTH_SECRET, { algorithms: ["HS256"] }) as JwtPayload & {
+        email: string;
+        surveyId: string;
+      };
+    } catch (primaryError) {
+      logger.error(primaryError, "Token verification failed with primary method");
+
+      // Fallback to legacy method (surveyId-based secret)
+      try {
+        payload = jwt.verify(token, NEXTAUTH_SECRET + surveyId, { algorithms: ["HS256"] }) as JwtPayload & {
+          email: string;
+        };
+      } catch (legacyError) {
+        logger.error(legacyError, "Token verification failed with legacy method");
+        throw new Error("Invalid token");
       }
-      const decryptedEmail = symmetricDecrypt(email, env.ENCRYPTION_KEY);
-      return decryptedEmail;
-    } catch {
-      // If decryption fails, return the original email (for older tokens)
-      return email;
     }
-  } catch (err) {
+
+    // Verify the surveyId matches if present in payload (new format)
+    if (payload.surveyId && payload.surveyId !== surveyId) {
+      return null;
+    }
+
+    const { email } = payload;
+    if (!email) {
+      return null;
+    }
+
+    // Decrypt email with fallback to plain text
+    if (!ENCRYPTION_KEY) {
+      return email; // Return as-is if encryption key not set
+    }
+
+    return decryptWithFallback(email, ENCRYPTION_KEY);
+  } catch (error) {
+    logger.error(error, "Survey link token verification failed");
     return null;
   }
 };
 
-export const verifyToken = async (token: string): Promise<JwtPayload> => {
-  // First decode to get the ID
-  const decoded = jwt.decode(token);
-  const payload: JwtPayload = decoded as JwtPayload;
+// Helper function to get user email for legacy verification
+const getUserEmailForLegacyVerification = async (
+  token: string,
+  userId?: string
+): Promise<{ userId: string; userEmail: string }> => {
+  if (!userId) {
+    const decoded = jwt.decode(token);
 
-  if (!payload) {
-    throw new Error("Token is invalid");
+    // Validate decoded token structure before using it
+    if (
+      !decoded ||
+      typeof decoded !== "object" ||
+      !decoded.id ||
+      typeof decoded.id !== "string" ||
+      decoded.id.trim() === ""
+    ) {
+      logger.error("Invalid token: missing or invalid user ID");
+      throw new Error("Invalid token");
+    }
+
+    userId = decoded.id;
   }
 
-  const { id } = payload;
-  if (!id) {
-    throw new Error("Token missing required field: id");
+  const decryptedId = decryptWithFallback(userId, ENCRYPTION_KEY);
+
+  // Validate decrypted ID before database query
+  if (!decryptedId || typeof decryptedId !== "string" || decryptedId.trim() === "") {
+    logger.error("Invalid token: missing or invalid user ID");
+    throw new Error("Invalid token");
   }
 
-  // Try to decrypt the ID (for newer tokens), if it fails use the ID as-is (for older tokens)
-  let decryptedId: string;
-  try {
-    decryptedId = symmetricDecrypt(id, env.ENCRYPTION_KEY);
-  } catch {
-    decryptedId = id;
-  }
-
-  // If no email provided, look up the user
   const foundUser = await prisma.user.findUnique({
     where: { id: decryptedId },
   });
 
   if (!foundUser) {
-    throw new Error("User not found");
+    const errorMessage = "User not found";
+    logger.error(errorMessage);
+    throw new Error(errorMessage);
   }
 
-  const userEmail = foundUser.email;
+  return { userId: decryptedId, userEmail: foundUser.email };
+};
 
-  return { id: decryptedId, email: userEmail };
+export const verifyToken = async (token: string): Promise<JwtPayload> => {
+  if (!NEXTAUTH_SECRET) {
+    throw new Error("NEXTAUTH_SECRET is not set");
+  }
+
+  let payload: JwtPayload & { id: string };
+  let userData: { userId: string; userEmail: string } | null = null;
+
+  // Try new method first, with smart fallback to legacy
+  try {
+    payload = jwt.verify(token, NEXTAUTH_SECRET, { algorithms: ["HS256"] }) as JwtPayload & {
+      id: string;
+    };
+  } catch (newMethodError) {
+    logger.error(newMethodError, "Token verification failed with new method");
+
+    // Get user email for legacy verification
+    userData = await getUserEmailForLegacyVerification(token);
+
+    // Try legacy verification with email-based secret
+    try {
+      payload = jwt.verify(token, NEXTAUTH_SECRET + userData.userEmail, {
+        algorithms: ["HS256"],
+      }) as JwtPayload & {
+        id: string;
+      };
+    } catch (legacyMethodError) {
+      logger.error(legacyMethodError, "Token verification failed with legacy method");
+      throw new Error("Invalid token");
+    }
+  }
+
+  if (!payload?.id) {
+    throw new Error("Invalid token");
+  }
+
+  // Get user email if we don't have it yet
+  userData ??= await getUserEmailForLegacyVerification(token, payload.id);
+
+  return { id: userData.userId, email: userData.userEmail };
 };
 
 export const verifyInviteToken = (token: string): { inviteId: string; email: string } => {
+  if (!NEXTAUTH_SECRET) {
+    throw new Error("NEXTAUTH_SECRET is not set");
+  }
+
+  if (!ENCRYPTION_KEY) {
+    throw new Error("ENCRYPTION_KEY is not set");
+  }
+
   try {
-    const decoded = jwt.decode(token);
-    const payload: JwtPayload = decoded as JwtPayload;
+    const payload = jwt.verify(token, NEXTAUTH_SECRET, { algorithms: ["HS256"] }) as JwtPayload & {
+      inviteId: string;
+      email: string;
+    };
 
-    const { inviteId, email } = payload;
+    const { inviteId: encryptedInviteId, email: encryptedEmail } = payload;
 
-    let decryptedInviteId: string;
-    let decryptedEmail: string;
-
-    try {
-      // Try to decrypt first (for newer tokens)
-      decryptedInviteId = symmetricDecrypt(inviteId, env.ENCRYPTION_KEY);
-      decryptedEmail = symmetricDecrypt(email, env.ENCRYPTION_KEY);
-    } catch {
-      // If decryption fails, use original values (for older tokens)
-      decryptedInviteId = inviteId;
-      decryptedEmail = email;
+    if (!encryptedInviteId || !encryptedEmail) {
+      throw new Error("Invalid token");
     }
 
+    // Decrypt both fields with fallback to original values
+    const decryptedInviteId = decryptWithFallback(encryptedInviteId, ENCRYPTION_KEY);
+    const decryptedEmail = decryptWithFallback(encryptedEmail, ENCRYPTION_KEY);
+
     return {
       inviteId: decryptedInviteId,
       email: decryptedEmail,
diff --git a/apps/web/modules/auth/lib/authOptions.test.ts b/apps/web/modules/auth/lib/authOptions.test.ts
index daaa2729c4..fb531e181a 100644
--- a/apps/web/modules/auth/lib/authOptions.test.ts
+++ b/apps/web/modules/auth/lib/authOptions.test.ts
@@ -1,12 +1,12 @@
+import { randomBytes } from "crypto";
+import { Provider } from "next-auth/providers/index";
+import { afterEach, describe, expect, test, vi } from "vitest";
+import { prisma } from "@formbricks/database";
 import { EMAIL_VERIFICATION_DISABLED } from "@/lib/constants";
 import { createToken } from "@/lib/jwt";
 // Import mocked rate limiting functions
 import { applyIPRateLimit } from "@/modules/core/rate-limit/helpers";
 import { rateLimitConfigs } from "@/modules/core/rate-limit/rate-limit-configs";
-import { randomBytes } from "crypto";
-import { Provider } from "next-auth/providers/index";
-import { afterEach, describe, expect, test, vi } from "vitest";
-import { prisma } from "@formbricks/database";
 import { authOptions } from "./authOptions";
 import { mockUser } from "./mock-data";
 import { hashPassword } from "./utils";
@@ -31,7 +31,7 @@ vi.mock("@/lib/constants", () => ({
   SESSION_MAX_AGE: 86400,
   NEXTAUTH_SECRET: "test-secret",
   WEBAPP_URL: "http://localhost:3000",
-  ENCRYPTION_KEY: "test-encryption-key-32-chars-long",
+  ENCRYPTION_KEY: "12345678901234567890123456789012", // 32 bytes for AES-256
   REDIS_URL: undefined,
   AUDIT_LOG_ENABLED: false,
   AUDIT_LOG_GET_USER_IP: false,
@@ -261,7 +261,7 @@ describe("authOptions", () => {
       vi.mocked(applyIPRateLimit).mockResolvedValue(); // Rate limiting passes
       vi.spyOn(prisma.user, "findUnique").mockResolvedValue(mockUser as any);
 
-      const credentials = { token: createToken(mockUser.id, mockUser.email) };
+      const credentials = { token: createToken(mockUser.id) };
 
       await expect(tokenProvider.options.authorize(credentials, {})).rejects.toThrow(
         "Email already verified"
@@ -280,7 +280,7 @@ describe("authOptions", () => {
         groupId: null,
       } as any);
 
-      const credentials = { token: createToken(mockUserId, mockUser.email) };
+      const credentials = { token: createToken(mockUserId) };
 
       const result = await tokenProvider.options.authorize(credentials, {});
       expect(result.email).toBe(mockUser.email);
@@ -303,7 +303,7 @@ describe("authOptions", () => {
           groupId: null,
         } as any);
 
-        const credentials = { token: createToken(mockUserId, mockUser.email) };
+        const credentials = { token: createToken(mockUserId) };
 
         await tokenProvider.options.authorize(credentials, {});
 
@@ -315,7 +315,7 @@ describe("authOptions", () => {
           new Error("Maximum number of requests reached. Please try again later.")
         );
 
-        const credentials = { token: createToken(mockUserId, mockUser.email) };
+        const credentials = { token: createToken(mockUserId) };
 
         await expect(tokenProvider.options.authorize(credentials, {})).rejects.toThrow(
           "Maximum number of requests reached. Please try again later."
@@ -339,7 +339,7 @@ describe("authOptions", () => {
           groupId: null,
         } as any);
 
-        const credentials = { token: createToken(mockUserId, mockUser.email) };
+        const credentials = { token: createToken(mockUserId) };
 
         await tokenProvider.options.authorize(credentials, {});
 
diff --git a/apps/web/modules/email/index.tsx b/apps/web/modules/email/index.tsx
index d8d1637b38..28c2b46a34 100644
--- a/apps/web/modules/email/index.tsx
+++ b/apps/web/modules/email/index.tsx
@@ -1,3 +1,12 @@
+import { render } from "@react-email/render";
+import { createTransport } from "nodemailer";
+import type SMTPTransport from "nodemailer/lib/smtp-transport";
+import { logger } from "@formbricks/logger";
+import type { TLinkSurveyEmailData } from "@formbricks/types/email";
+import { InvalidInputError } from "@formbricks/types/errors";
+import type { TResponse } from "@formbricks/types/responses";
+import type { TSurvey } from "@formbricks/types/surveys/types";
+import { TUserEmail, TUserLocale } from "@formbricks/types/user";
 import {
   DEBUG,
   MAIL_FROM,
@@ -17,15 +26,6 @@ import { getOrganizationByEnvironmentId } from "@/lib/organization/service";
 import NewEmailVerification from "@/modules/email/emails/auth/new-email-verification";
 import { EmailCustomizationPreviewEmail } from "@/modules/email/emails/general/email-customization-preview-email";
 import { getTranslate } from "@/tolgee/server";
-import { render } from "@react-email/render";
-import { createTransport } from "nodemailer";
-import type SMTPTransport from "nodemailer/lib/smtp-transport";
-import { logger } from "@formbricks/logger";
-import type { TLinkSurveyEmailData } from "@formbricks/types/email";
-import { InvalidInputError } from "@formbricks/types/errors";
-import type { TResponse } from "@formbricks/types/responses";
-import type { TSurvey } from "@formbricks/types/surveys/types";
-import { TUserEmail, TUserLocale } from "@formbricks/types/user";
 import { ForgotPasswordEmail } from "./emails/auth/forgot-password-email";
 import { PasswordResetNotifyEmail } from "./emails/auth/password-reset-notify-email";
 import { VerificationEmail } from "./emails/auth/verification-email";
@@ -111,7 +111,7 @@ export const sendVerificationEmail = async ({
 }): Promise<boolean> => {
   try {
     const t = await getTranslate();
-    const token = createToken(id, email, {
+    const token = createToken(id, {
       expiresIn: "1d",
     });
     const verifyLink = `${WEBAPP_URL}/auth/verify?token=${encodeURIComponent(token)}`;
@@ -136,7 +136,7 @@ export const sendForgotPasswordEmail = async (user: {
   locale: TUserLocale;
 }): Promise<boolean> => {
   const t = await getTranslate();
-  const token = createToken(user.id, user.email, {
+  const token = createToken(user.id, {
     expiresIn: "1d",
   });
   const verifyLink = `${WEBAPP_URL}/auth/forgot-password/reset?token=${encodeURIComponent(token)}`;